                     FOR PUBLICATION
  UNITED STATES COURT OF APPEALS
       FOR THE NINTH CIRCUIT

RICKY LEE EARP,                             
               Petitioner-Appellant,
                                                    No. 03-99005
                 v.
JOHN STOKES, Warden, of                              D.C. No.
                                                   CV-00-06508-R
California State Prison at San
                                                      OPINION
Quentin,*
              Respondent-Appellee.
                                            
         Appeal from the United States District Court
            for the Central District of California
          Manuel L. Real, District Judge, Presiding

                     Argued and Submitted
              July 14, 2005—Pasadena, California

                     Filed September 8, 2005

        Before: Jerome Farris, Dorothy W. Nelson, and
             Richard C. Tallman, Circuit Judges.

                    Opinion by Judge Tallman




   *Pursuant to Fed. R. App. P. 43(c)(2), John Stokes, the current custo-
dian, is substituted for Jeanne S. Woodford as Warden of California State
Prison at San Quentin.

                                 12699
                     EARP v. STOKES                12703


                      COUNSEL

Robert S. Gerstein, Santa Monica, California, for the
petitioner-appellant.

James William Bilderback II, Deputy Attorney General, Los
Angeles, California, for the respondent-appellee.
12704                         EARP v. STOKES
                                OPINION

TALLMAN, Circuit Judge:

   Ricky Lee Earp is on death row in San Quentin, California,
after being convicted in Los Angeles County of the 1988 rape
and murder of eighteen-month-old Amanda Doshier. The jury
convicted Earp of first-degree murder and found three death-
qualifying special circumstances to be true: rape, sodomy, and
lewd and lascivious conduct on a child under the age of four-
teen. In the separate penalty phase, the jury recommended that
Earp be put to death for his crimes. The California Superior
Court (“trial court”) imposed that sentence on February 21,
1992.

   All reviewing courts thus far have upheld Earp’s conviction
and sentence. The California Supreme Court (“state court”)
affirmed Earp’s conviction and death sentence on direct
appeal, and summarily denied his state habeas corpus petition
on the merits without affording him an evidentiary hearing on
any of his claims. People v. Earp, 978 P.2d 15 (Cal. 1999).
The United States Supreme Court denied certiorari. Earp v.
California, 529 U.S. 1005 (2000). Earp then filed a federal
habeas corpus petition in the United States District Court for
the Central District of California, raising nineteen constitu-
tional claims. The district court denied Earp’s habeas petition
on all of them. Earp now brings this appeal.

   We affirm the district court on seven of the claims Earp
raises in this appeal, and vacate and remand for an evidentiary
hearing on the two remaining claims.1 This Opinion addresses
  1
   In a separately filed companion Memorandum Disposition we affirm
the district court on six of Earp’s claims. Earp made four prosecutorial
misconduct claims in addition to the one discussed in this Opinion: (1) that
the prosecutor committed prejudicial error under Doyle v. Ohio, 426 U.S.
610 (1976), by commenting on Earp’s failure to name Dennis Morgan
prior to trial; (2) that the prosecutor’s closing statement shifted the burden
                             EARP v. STOKES                          12705
Earp’s claims of prosecutorial misconduct, ineffective assis-
tance of counsel, and conflict of interest.2 The district court
conducted a limited evidentiary hearing on his conflict claim
and denied his motion for an evidentiary hearing on his pro-
secutorial misconduct and ineffective assistance of counsel
claims. Ultimately, all of these claims were denied on sum-
mary judgment.

   Here we decide whether: (1) Earp alleges facts warranting
an evidentiary hearing on his claim that the prosecutor com-
mitted prejudicial misconduct by dissuading Michael Taylor
from testifying; (2) Earp alleges facts warranting an evidenti-
ary hearing on his claim of ineffective assistance of counsel
for failure to sufficiently investigate mitigation evidence; and
(3) Earp’s counsel suffered from a conflict of interest stem-
ming from her intimate relationship with Earp during his trial
and sentencing. We hold that Earp has alleged facts which, if
proven true, may entitle him to relief on his prosecutorial mis-
conduct and ineffective assistance of counsel claims. Because

of proof; (3) that the prosecutor impermissibly stated his own opinion of
Earp’s guilt; and (4) that the cumulative effect of these errors deprived
Earp of his right to due process. We affirm the district court’s summary
judgment order in favor of the Warden because we agree that the state
court’s resolution denying these claims was neither contrary to, nor an
unreasonable application of, controlling federal precedent. Furthermore,
we affirm in the Memorandum Disposition the district court’s decision to
deny Earp an evidentiary hearing on his claims that his counsel provided
ineffective assistance by not presenting his third-party defense in the open-
ing statement and by eliciting testimony from a defense investigator.
Because the record demonstrates that these were strategic choices, we hold
in the Memorandum Disposition that the district court did not abuse its
discretion by denying an evidentiary hearing on these claims.
   2
     For the remainder of this Opinion, we use the term “prosecutorial mis-
conduct” to refer to Earp’s claim that the prosecutor intimidated and
threatened Michael Taylor to dissuade him from testifying, and the term
“ineffective assistance of counsel” to refer to Earp’s claim that his counsel
provided ineffective assistance by failing to conduct adequate investiga-
tion into mitigating evidence for use in the penalty phase.
12706                      EARP v. STOKES
Earp has never been afforded an evidentiary hearing on these
claims, we remand to the district court for an evidentiary
hearing on his prosecutorial misconduct and ineffective assis-
tance of counsel claims. As to Earp’s conflict claim, we hold
that the state court determination that counsel was not labor-
ing under a conflict of interest was neither contrary to, nor an
unreasonable application of, established federal law because
the Supreme Court has expressly limited its conflict jurispru-
dence to cases involving multiple, concurrent representation.
We therefore affirm the summary judgment in part, reverse in
part, and remand for the necessary evidentiary proceedings.

                                   I

   We recount the facts and circumstances leading to and sur-
rounding the crime and Earp’s trial as necessary to understand
our opinion.3 In August 1988, Earp was living in Palmdale,
California, with his girlfriend, Virginia MacNair. On August
22, Cindy Doshier left her daughter, Amanda Doshier, with
Earp and MacNair for a few days, as she had done several
times before. On Thursday, August 25, MacNair left for work
around 7:00 a.m., leaving Amanda with Earp. Around 3:00
p.m., a firefighter responded to an emergency call from a man
reporting that a baby had fallen down some stairs. A prelimi-
nary assessment of her injuries led the first responder to con-
clude that Amanda needed more medical attention than he
could give, so the firefighter took her to the hospital.

   After the firefighter left with Amanda, Earp disappeared
and spent the next two days with different sets of friends and
family elsewhere in California before ultimately turning him-
self in to the police in Sacramento after learning that he was
being sought in connection with Amanda’s death. During the
intervening time, Earp gave inquiring friends and neighbors a
  3
   We extract much of the facts and procedural history from the Califor-
nia Supreme Court opinion disposing of Earp’s direct appeal, Earp, 978
P.2d at 27-31, confirmed by our own independent review of the record.
                        EARP v. STOKES                    12707
host of contradictory explanations for Amanda’s injuries and
his absence.

  At 10:30 a.m. on Saturday, August 27, 1988, Amanda died.
Medical examinations of Amanda revealed that she had
severe bruising, blood, and tears in the rectal area and blood
and gaping in the vaginal area consistent with sexual assault.
However, no semen, sperm, or seminal fluid was found. The
medical examiner determined that Amanda’s death was
caused either by multiple sharp blows to the top of the head
or severe shaking.

   At trial, Earp denied sexually molesting or otherwise harm-
ing Amanda. He blamed Dennis Morgan, Amanda’s grand-
mother’s boyfriend whom Earp had met while the two served
time together in prison. Dennis Morgan testified that he met
Earp while they were both inmates at the Susanville prison
and had helped Earp get a job after his release. He also admit-
ted that he was a heroin addict with nineteen different aliases,
but refuted Earp’s assertion that he was present at MacNair’s
house on August 25, denied knowing where Earp was living
at the time, and claimed that he did not rape or molest
Amanda. He also accused Earp of asking him to testify that
there was a man named Joe at the house with them, and
alleged that Paul Ford, a defense investigator, told him that
Earp “needed someone who could place somebody else at the
house.”

  At the penalty phase, Adrienne Dell, Earp’s attorney, pre-
sented the following evidence in mitigation: Earp’s mother
and aunt testified generally about Earp’s family background
and legal troubles as a juvenile; MacNair testified as to her
and her son’s visits to Earp in jail; a cook from the California
Youth Authority (“CYA”) testified about Earp during his
juvenile confinement; and a former associate warden at San
Quentin testified that Earp would pose no danger in a high-
security facility and that Earp could adjust to life in prison.
12708                   EARP v. STOKES
                               II

   We review de novo the district court’s denial of a petition
for a writ of habeas corpus, Lambert v. Blodgett, 393 F.3d
943, 964 (9th Cir. 2004), and the district court’s grant of sum-
mary judgment, Davis v. Woodford, 384 F.3d 628, 638 (9th
Cir. 2004). “Factual findings and credibility determinations
made by the district court in the context of granting or deny-
ing the petition are reviewed for clear error.” Lambert, 393
F.3d at 964. The district court’s application of the Antiterro-
rism and Effective Death Penalty Act of 1996 (“AEDPA”), as
well as its conclusion that the standards set forth in AEDPA
are satisfied, is a mixed question of law and fact which we
also review de novo. Id. at 965.

   Because Earp’s petition was filed after April 24, 1996, fed-
eral review is circumscribed by AEDPA. Lockyer v. Andrade,
538 U.S. 63, 70 (2003); see also Lambert, 393 F.3d at 965
(citing Woodford v. Garceau, 538 U.S. 202, 210 (2003)).
AEDPA mandates a highly deferential standard for reviewing
state court determinations. Under AEDPA, a writ of habeas
corpus:

    shall not be granted with respect to any claim that
    was adjudicated on the merits in State court proceed-
    ings unless the adjudication of the claim—

    (1) resulted in a decision that was contrary to, or
    involved an unreasonable application of, clearly
    established federal law, as determined by the
    Supreme Court of the United States; or

    (2) resulted in a decision that was based on an unrea-
    sonable determination of the facts in light of the evi-
    dence presented in the State court proceeding.

28 U.S.C. § 2254(d).
                        EARP v. STOKES                     12709
   We review de novo the district court’s interpretation of
AEDPA standards governing the grant or denial of an eviden-
tiary hearing, Baja v. Ducharme, 187 F.3d 1075, 1077 (9th
Cir. 1999), and we review for abuse of discretion the district
court’s ultimate denial of an evidentiary hearing based on
these AEDPA standards, Davis, 384 F.3d at 638. In determin-
ing whether a petitioner is entitled to an evidentiary hearing
under AEDPA, the district court:

    must determine whether a factual basis exists in the
    record to support the petitioner’s claim. If it does
    not, and an evidentiary hearing might be appropriate,
    the court’s first task in determining whether to grant
    an evidentiary hearing is to ascertain whether the
    petitioner has ‘failed to develop the factual basis of
    a claim in State court.’ . . . . If [ ] the applicant has
    not ‘failed to develop’ the facts in state court, the
    district court may proceed to consider whether a
    hearing is appropriate or required under Townsend v.
    Sain, 372 U.S. 293 (1963)[ overruled on other
    grounds in Keeney v. Tamayo-Reyes, 504 U.S. 1, 5
    (1992)].

Insyxiengmay v. Morgan, 403 F.3d 657, 669-70 (9th Cir.
2005) (quoting Baja, 187 F.3d at 1078). Townsend establishes
that a defendant is entitled to an evidentiary hearing if he can
show that:

    (1) the merits of the factual dispute were not
    resolved in the state hearing; (2) the state factual
    determination is not fairly supported by the record as
    a whole; (3) the fact-finding procedure employed by
    the state court was not adequate to afford a full and
    fair hearing; (4) there is a substantial allegation of
    newly discovered evidence; (5) the material facts
    were not adequately developed at the state-court
    hearing; or (6) for any reason it appears that the state
12710                         EARP v. STOKES
      trier of fact did not afford the habeas applicant a full
      and fair hearing.

Townsend, 372 U.S. at 313.

  [1] Accordingly, where the petitioner establishes a color-
able claim4 for relief and has never been afforded a state or
federal hearing on this claim, we must remand to the district
court for an evidentiary hearing. Insyxiengmay, 403 F.3d at
670; Stankewitz v. Woodford, 365 F.3d 706, 708 (9th Cir.
2004); Phillips v. Woodford, 267 F.3d 966, 973 (9th Cir.
2001). In other words, a hearing is required if: “(1) [the defen-
dant] has alleged facts that, if proven, would entitle him to
habeas relief, and (2) he did not receive a full and fair oppor-
tunity to develop those facts[.]” Williams v. Woodford, 384
F.3d 567, 586 (9th Cir. 2004).

                                     III

   In his state habeas petition and again in his federal petition,
Earp argues that the prosecutor committed misconduct by
intimidating a post-trial witness named Michael Taylor to pre-
vent him from testifying in support of a new trial motion. We
hold that the district court’s decision to reject this claim with-
out holding an evidentiary hearing was an abuse of discretion.
See Davis, 384 F.3d at 638.

                                     A

                                      1

   The case against Earp was comprised of strong circumstan-
tial evidence — Amanda had been left in his care on the day
of the crime, and after Amanda was taken to the hospital Earp
  4
   In showing a colorable claim, a petitioner is “required to allege specific
facts which, if true, would entitle him to relief.” Ortiz v. Stewart, 149 F.3d
923, 934 (9th Cir. 1998) (internal quotation marks and citation omitted).
                          EARP v. STOKES                 12711
disappeared and gave false and inconsistent explanations of
what had happened to her before he surrendered to the police.
At trial, the defense case hinged on a credibility battle
between Earp, who claimed that Dennis Morgan had mur-
dered Amanda, and Morgan, who testified that he had never
seen Amanda or been to the house where she was fatally
injured.

   Earp testified that on the day Amanda was attacked, he was
at home watching her and working around the house when he
was interrupted by Morgan’s arrival at his door. Earp claimed
that he allowed Morgan into the house, but largely ignored
him, hoping that he would leave. Later in the afternoon, Earp
said he went outside to clean paintbrushes and, because the
backyard was unfinished, Earp left Amanda inside with Mor-
gan and the family dog. Earp testified that after approximately
a half-hour, he noticed the dog was agitated and he went
inside to investigate. He discovered Amanda lying motionless
at the bottom of the stairs, and made a number of attempts to
revive her, including performing CPR, before calling emer-
gency services. Earp further testified that Morgan left as Earp
was calling for help.

   Morgan’s testimony contradicted this defense. Morgan tes-
tified that he had never been in the home and did not even
know where it was. He also testified that he had never seen
Amanda, and that he had not molested or raped her. Notably,
no trial witness other than Earp was able to place Morgan at
the house on the day of the crime.

                                  2

   After the trial was over, a defense investigator located a
potential jailhouse witness who might have impeached Mor-
gan’s testimony: Michael Taylor. Taylor was also an inmate
at the Los Angeles County Central Jail at the time of Earp’s
trial, where both Earp and Morgan were being held.5 In a
  5
   Morgan was jailed on unrelated charges.
12712                         EARP v. STOKES
series of declarations, Taylor claims that, while Earp’s jury
was deliberating, he overheard Morgan tell another inmate
that Morgan had visited the house where Earp was watching
Amanda on the day in question. Taylor insists that Morgan
referred to Amanda as his “granddaughter,” and expressed
fear that Earp would “come after him” if he got out of jail
because of Morgan’s false testimony at trial.

   Taylor declares that he initially told this story in a recorded
statement to the defense in late 1991 or early 1992. He asserts
that, later the same day, the prosecutor and a sheriff’s deputy
took him to a private room at the jail, verbally abused him,
and told him that he would never get out if he stood by his
statement. Taylor insists that although his initial statement
was true, he capitulated in the face of the prosecutor’s threats
and retracted the statement.

                                     B

   Earp first raised his claim that these events constituted pro-
secutorial misconduct in his state habeas petition.6 He argued
in his petition that the prosecutor violated Earp’s due process
rights by intimidating Taylor into withdrawing his declara-
tion. He supported his state petition with four signed declara-
  6
    Michael Taylor’s potential testimony arose in two other ways in the
state habeas litigation, but Earp does not pursue those arguments in this
appeal. First, Earp partially based his Motion for a New Trial on the argu-
ment that Taylor’s potential testimony was newly discovered evidence.
The trial court denied Earp’s motion for a new trial, and the denial was
affirmed on direct appeal. Earp dropped this argument after direct appeal;
he did not protest the new trial decision in his state or federal habeas peti-
tions. Earp’s second use of Taylor’s potential testimony was in his state
habeas petition to support his claim of factual innocence. The state court
summarily denied this claim, but Earp raised it again in his federal peti-
tion. Holding that there is no free-standing constitutional claim of factual
innocence, the district court rejected this claim, and Earp has abandoned
it on appeal. It is only his third use of Taylor’s proffered testimony — to
support his claim that the prosecutor committed misconduct — that Earp
continues to pursue in this appeal.
                         EARP v. STOKES                    12713
tions from Taylor, a signed declaration from defense
investigator Manuel Alvarez, a declaration from Adrienne
Dell, Earp’s trial attorney, and a transcript of part of the pros-
ecutor’s interview with Taylor. Through these submissions to
the state court, Earp proffered the factual foundation for his
alleged prosecutorial misconduct claim. See id. at 669-70.

   Without conducting a hearing, the state court denied Earp’s
prosecutorial misconduct claim without opinion. Earp contin-
ued to pursue his prosecutorial misconduct claim in his fed-
eral petition. He was unsuccessful before the district court as
well; the federal court adopted the Warden’s proposed order
granting summary judgment against Earp on his prosecutorial
misconduct claim. Earp appeals the district court’s order.

                                C

  Because the factual basis for Earp’s claim was adequately
proffered to the state court, he is entitled to an evidentiary
hearing if he has not previously received a full and fair oppor-
tunity to develop the facts of his claim and he presents a “col-
orable claim” for relief. Insyxiengmay, 403 F.3d at 669-70;
see also Williams, 384 F.3d at 586.

                                1

   [2] It is evident from the record that Earp has never
received an opportunity to develop his claim of prosecutorial
misconduct. The issue was not presented to the trial court, but
it was raised on habeas, and neither the state court nor the dis-
trict court allowed him an evidentiary hearing. Because we
find that such a hearing was necessary to make the credibility
determination upon which rejection of Earp’s claim depends,
we conclude that he has not had a “full and fair” opportunity
to develop the facts supporting his claim. See Townsend, 372
U.S. at 313.
12714                         EARP v. STOKES
   [3] The district court resolved Earp’s claim on the basis of
Taylor’s credibility, concluding that Taylor’s declarations
were “inherently untrustworthy and not worthy of belief.”7
The district court reached its credibility determination without
taking the opportunity to listen to Taylor, test his story, and
gauge his demeanor.8 See Blackledge v. Allison, 431 U.S. 63,
82 n.25 (1977) (“When the issue is one of credibility, resolu-
tion on the basis of affidavits can rarely be conclusive . . . .”)
(internal quotation marks and citation omitted).

   [4] In rare instances, credibility may be determined without
an evidentiary hearing where it is possible to “conclusively”
decide the credibility question based on “documentary testi-
mony and evidence in the record.” Watts v. United States, 841
F.2d 275, 277 (9th Cir. 1988) (finding an evidentiary hearing
unnecessary in a § 2255 case). However, such a determination
is not possible here because the documentary testimony in the
record is consistent with Taylor’s story and Earp’s claim. Oth-
erwise, there is no evidentiary basis for the district court’s
judgment of Taylor’s incredibility because Taylor’s story is
completely outside the record. See Frazer v. United States, 18
F.3d 778, 784 (9th Cir. 1994) (“Because all of these factual
  7
     The district court also found that Taylor’s statements would not have
impacted Earp’s conviction and thus “did not concern material evidence”
because the trial court would not have accepted them. This is also a credi-
bility determination, because the district court reasoned that the trial court
would have found the declarations untrustworthy and refused to consider
them.
   8
     The district court gave no explanation as to how it resolved the credi-
bility contest between Taylor and the law enforcement officers in favor of
the officers. One could speculate that the district court found Taylor
untrustworthy because he was an inmate, but, in the absence of an eviden-
tiary hearing to determine who was telling the truth, it remains unclear
why an inmate testifying for the defense would be inherently incredible.
Alternatively, one could speculate that the district court found Taylor
untrustworthy because he changed his initial story, and then returned to it.
But Earp’s allegation is that Taylor changed his story because the prosecu-
tor essentially threatened him, so this speculation would support Earp’s
allegation if the evidence Earp proffers is found to be credible.
                         EARP v. STOKES                    12715
allegations were outside the record, this claim on its face
should have signalled the need for an evidentiary hearing.”).

   [5] Because the veracity of the witnesses who signed the
affidavits on which Earp based his claim was at issue, the
claim could not be adjudicated without an evidentiary hearing
on this disputed issue of material fact. Summary judgment is
an inappropriate vehicle for resolving claims that depend on
credibility determinations. See Williams v. Calderon, 48 F.
Supp. 2d 979, 989 (C.D. Cal. 1998) (noting in the context of
a habeas claim “[t]he Court is not to determine issues of cred-
ibility on a motion for summary judgment; instead, the truth
of each party’s affidavits is assumed”), aff’d Williams, 384
F.3d at 628; see also United States v. Two Tracts of Land in
Cascade County, Mont., 5 F.3d 1360, 1362 (9th Cir. 1993)
(reversing and remanding summary judgment for live testi-
mony where the district court concluded on the basis of affi-
davits that the affiants were not credible); Kreisner v. San
Diego, 988 F.2d 883, 900 n.1)(“Determinations of credibility
are inappropriate for summary judgment.”), amended by 1
F.3d 775 (9th Cir. 1993); SEC v. Koracorp Indus., Inc., 575
F.2d 692, 699 (9th Cir. 1978) (“[S]ummary judgment is sin-
gularly inappropriate when credibility is at issue.”).

   Earp has never had an opportunity to present Taylor’s live
testimony so that the trier of fact can judge his credibility, and
the prosecutor and sheriff’s deputy have never been ques-
tioned regarding their side of the story. Thus, we conclude
that Earp has not had a full and fair opportunity to develop the
facts to support his claim.

                                2

   We next consider whether Earp has alleged facts which, if
demonstrated to be true, would present a colorable claim for
relief. See Insyxiengmay, 403 F.3d at 669-70; Williams, 384
F.3d at 586. At this stage, Earp does not need to prove that
the prosecutor committed misconduct or that his due process
12716                        EARP v. STOKES
rights were violated; he only needs to allege a colorable claim
for relief. See Phillips, 267 F.3d at 973. This is a low bar, and
Earp has surmounted it.

   [6] If the facts that Earp alleges are proven true at an evi-
dentiary hearing, the district court might well determine that
he had established that the prosecutor threatened and verbally
abused Taylor, fed him an untrue story, forced him to recant
the impeaching statement by Morgan on tape, and punished
Taylor for assisting Earp by having Taylor removed from his
job as a trustee and transferred to a significantly less desirable
jail facility. It is well established that “substantial government
interference with a defense witness’s free and unhampered
choice to testify amounts to a violation of due process.”
United States v. Vavages, 151 F.3d 1185, 1188 (9th Cir. 1998)
(quoting United States v. Little, 753 F.2d 1420, 1438 (9th Cir.
1984)). Moreover, coercive or threatening behavior towards a
potential witness may justify reversal of a defendant’s convic-
tion. See Webb v. Texas, 409 U.S. 95, 98 (1972); Williams,
384 F.3d at 601-02 (“Undue prosecutorial interference in a
defense witness’s decision to testify arises when the prosecu-
tion intimidates or harasses the witness to discourage the wit-
ness from testifying . . . .”). If Earp could prove his factual
claims at an evidentiary hearing, he may well establish that
the prosecutor committed misconduct.9 We note that we are
  9
    We have considered and rejected the possibility that hearsay objections
to Taylor’s testimony would preclude Earp’s claim. Hearsay testimony
should not be necessary in the district court because in order to establish
Earp’s claim, Taylor would need to testify as to how the prosecutor treated
him and how he reacted (by withdrawing his statement); the actual content
of Taylor’s statement would not be particularly relevant to this inquiry. If
Earp is granted relief on this claim and the case against him ultimately
retried, Taylor’s testimony would likely be admissible under California
evidence rules as an inconsistent statement, see Cal. Evid. Code §§ 770,
1235, as impeachment evidence, see Cal. Evid. Code §§ 780(h), 785, or
possibly also as a statement against penal interest, see Cal. Evid. Code
§ 1230. We thus conclude that hearsay concerns do not preclude a finding
that Earp has alleged facts which, if proven, would entitle him to relief.
                             EARP v. STOKES                          12717
not opining on what the resolution of this issue should be; we
are only explaining why Earp is entitled to a hearing on his
claim.

   [7] Earp has also made out at least a colorable claim that
he was prejudiced by the prosecutor’s misconduct. If the facts
Earp alleges are true, he may well have demonstrated that the
prosecutor’s misconduct precluded him from presenting his
full defense. See Chambers v. Mississippi, 410 U.S. 284, 302
(1973) (“Few rights are more fundamental than that of an
accused to present witnesses in his own defense.”). Further-
more, because Earp’s defense strategy at trial so clearly pitted
Earp’s credibility against Morgan’s, evidence that Morgan
was lying could have created a reasonable doubt with the jury
that would have made the difference for Earp. See Silva v.
Brown, No. 04-99000, 2005 WL 1732765, *5 (9th Cir. Jul.
26, 2005) (“Impeachment evidence is especially likely to be
material when it impugns the testimony of a witness who is
critical to the prosecution’s case.”). If Earp can demonstrate
that prosecutorial misconduct prevented Taylor from
impeaching Morgan, he may be able to establish that he was
deprived of his right to present Taylor as a witness on his
behalf, that he should have been granted a new trial to prove
his defense, and that this deprivation may well have affected
the outcome.

   The district court’s conclusion that Earp has not demon-
strated any potential prejudice hinges on the credibility deter-
mination that we have already concluded cannot be made on
summary judgment. The district court says that it assumed the
credibility of Taylor’s declarations, but concluded that even if
the prosecutor committed misconduct, Earp was not preju-
diced because the trial court would not have accepted Tay-
lor’s testimony had it been offered because the court would
not have found it credible.10 Had the trial court actually heard
  10
    The district court reached this conclusion by adopting the trial court’s
conclusion that Taylor was untrustworthy. Just as we could not accept the
12718                        EARP v. STOKES
Taylor testify and determined that he was not credible, we
would probably defer to the trial court’s credibility judgment
as an established fact and would likely conclude that Earp had
not raised a colorable claim of prejudice. See Torres v.
Prunty, 223 F.3d 1103, 1109 (9th Cir. 2000). However,
because no court has properly considered Taylor’s credibility,
we have no basis upon which we may hold that the facts Earp
alleges do not establish a colorable claim of prejudice by pro-
secutorial misconduct.

   Instead, we hold that Earp has established entitlement to an
evidentiary hearing because the facts he alleged may show
that the prosecutor committed a constitutional due process
violation by prejudicially dissuading Michael Taylor from tes-
tifying. We remand for an evidentiary hearing so that Earp
will have an opportunity to prove the facts supporting his
claim.

                                    IV

   Earp argues that he was denied effective assistance because
his counsel’s investigation was insufficient, resulting in a
“large body of relevant mitigating material” being kept from
the jury in the penalty phase. Specifically, Earp argues that
defense counsel’s failure to properly investigate and follow up
on leads unearthed by the defense investigator resulted in the
failure to uncover and present the following mitigating evi-
dence: (1) extensive records of Earp’s schooling, document-
ing a history of emotional problems and possible
psychological or neurological problems; (2) further informa-
tion about Earp’s family background, his history of substance
abuse and mental problems, especially in light of his family
history of alcoholism, depression, and suicide; and (3) neuro-

district court’s credibility judgment based only on Taylor’s written state-
ments, we cannot accept its reliance upon a trial court credibility judgment
that suffered from the same deficiency in resolving a credibility dispute
without a hearing.
                             EARP v. STOKES                          12719
logical and psychiatric evaluations evincing organic brain
damage resulting from head trauma that he suffered at age
eight or nine. In this appeal, Earp seeks not the grant of his
petition for relief, but remand for an evidentiary hearing on
this claim.11

  The district court denied Earp’s motion for an evidentiary
hearing and granted summary judgment in favor of the War-
den on this claim, concluding that Earp failed to establish that
counsel’s performance was deficient and that he suffered prej-
udice thereby, because the evidence in aggravation was insur-
mountable.12 Because we find that Earp has met the
  11
      Earp also raised this claim in his state petition for habeas relief. In
support of his claims at the state level Earp included the following items
in his exhibits: the declaration of Lori Thomson, Earp’s sister; Earp’s
CYA records; Earp’s juvenile arrest/detention record; Earp’s Santa Clara
Valley Medical Center records; Earp’s school records including progress
reports, psychological reports, and testing results; Earp’s Probation Offi-
cer’s Social Study Report; birth, school, and medical records of Earp’s
extended and immediate family members; and various reports about the
conditions of CYA confinement.
   12
      The district court had before it all of the evidence contained in the
state record, along with the following: the declaration of Barbara Nus-
baum, Earp’s aunt; the declaration of Helen Perusse, Earp’s mother; the
declaration of Curtis Earp, Earp’s brother; Background Factors and Social
History (prepared by defense investigator Sheryl Duvall for the trial court
on January 23, 1992); the declaration of Douglas Dorman (re: teenage
drug use, family background, time in detention); the declaration of Donald
Robbins (re: family background, alcoholism, abuse, teenage drug use, time
in detention); the declaration of Kelly Williams (re: teenage drug use, fam-
ily background); the supplemental declaration of Barbara Nusbaum (re:
alcohol abuse, family background, teenage drug use); the supplemental
declaration of Curtis Earp (re: family background, father’s abuse of Earp,
father’s suicide); the declaration of Abbey Drew (re: experience as Earp’s
Juvenile Hall counselor, Earp’s behavior, impressions of Earp as a teen-
ager); the declaration of Dean R. Gits (re: contents of the deposition of
Sue Brown); the Expert Report of Ines Monguio, Ph.D. (re: whether
Earp’s psychosocial history and neuropsychological functioning prior to
and during the crime for which he was convicted may have presented a
viable defense at the time because Earp’s test results and records were
“consistent with organic damage[ ] by traumatic brain injury”); and the
Expert Report of Ezekiel P. Perlo (re: expert opinion as to ineffective
assistance, mostly addressing the conflict claim).
12720                   EARP v. STOKES
requirements for an evidentiary hearing by alleging facts that,
if proven, may entitle him to relief, and because these allega-
tions have never been considered in an evidentiary hearing,
we order a remand for that purpose.

                               A

   [8] In order to establish entitlement to an evidentiary hear-
ing, Earp is not required to conclusively establish in this
appeal that counsel was prejudicially deficient. Rather, Earp
must demonstrate by his evidence the potential of a colorable
claim that, if proven true at the hearing, would show that his
former counsel’s failure to investigate amounted to ineffective
assistance of counsel, and that, but for such deficient repre-
sentation, there is a reasonable probability that the outcome of
the proceeding would have been different. See Strickland v.
Washington, 466 U.S. 668, 688, 693-94 (1984).

                               B

   A defendant in a criminal proceeding is entitled to effective
assistance of counsel in order “to protect the fundamental
right to a fair trial.” Id. at 684. Strickland sets forth two
prongs that the defendant must satisfy in order to establish a
Sixth Amendment right to counsel violation: (1) “the defen-
dant must show that counsel’s performance was deficient”;
and (2) “the defendant must show that the deficient perfor-
mance prejudiced the defense . . . . Unless a defendant makes
both showings, it cannot be said that the conviction or death
sentence resulted from a breakdown in the adversary process
that renders the result unreliable.” Id. at 687.

   In order to satisfy the first prong, “the defendant must show
that counsel’s representation fell below an objective standard
of reasonableness” under “prevailing professional norms,” id.
at 688, by identifying the acts or omissions “that are alleged
not to have been the result of reasonable professional judg-
ment[,]” id. at 690. Our review of counsel’s performance for
                         EARP v. STOKES                    12721
constitutional deficiency “must be highly deferential” and
should include every effort “to eliminate the distorting effects
of hindsight[.]” Id. at 689.

   It is not enough to show that counsel was deficient; rather,
reversal is only proper if the error had a prejudicial effect on
the outcome of the trial. Id. at 692. Thus, in order to establish
prejudice, the “defendant must show that there is a reasonable
probability that, but for counsel’s unprofessional errors, the
result of the proceeding would have been different. A reason-
able probability is a probability sufficient to undermine confi-
dence in the outcome.” Id. at 694.7

                               C

                               1

   Two recent Supreme Court cases inform our analysis of
Earp’s claim. First, in Williams v. Taylor, 529 U.S. 362
(2000), where the defendant faced death because the jury
found a probability of future dangerousness, the Supreme
Court considered whether counsel’s failure to discover, inves-
tigate, and present certain mitigating evidence fell “below the
range expected of reasonable, professional competent assis-
tance of counsel.” Id. at 371 (internal quotation marks and
citation omitted). At sentencing, counsel presented testimony
from Williams’s mother and two neighbors, and a taped
excerpt from a psychiatrist. Id. at 369. The witnesses testified
generally that Williams was a “nice boy,” and a non-violent
person by nature. Id. The psychiatrist’s taped excerpt related
statements made by Williams that, in a prior unrelated rob-
bery, Williams had removed the bullets from his gun in order
to ensure that he did not hurt anyone. Id.

  Reversing the Fourth Circuit’s denial of habeas relief, the
Supreme Court held that, notwithstanding the presentation of
some mitigation evidence, “trial counsel did not fulfill their
obligation to conduct a thorough investigation of [Williams’s]
12722                   EARP v. STOKES
background.” Id. at 396 (citation omitted). Specifically, the
Court noted that, despite being put on notice of Williams’s
cooperation in a prison sting, counsel requested neither prison
records nor testimony from prison officials regarding Wil-
liams’s non-violent disposition. Id. Counsel also failed to
return a phone call from a witness who offered to testify on
Williams’s behalf. Id.

   [9] Wiggins v. Smith, 539 U.S. 510 (2003), is also particu-
larly instructive in the instant appeal. There, the Supreme
Court further refined and emboldened the ineffective assis-
tance inquiry in the context of a claimed failure to investigate
mitigation evidence. The Court held that, in determining
whether counsel exercised “reasonable professional judg-
ment[,]” Strickland, 466 U.S. at 691, the focus is “on whether
the investigation supporting counsel’s decision not to intro-
duce mitigating evidence of Wiggins’ background was itself
reasonable[,]” not “whether counsel should have presented”
mitigation evidence, Wiggins, 539 U.S. at 522-23.

   The Court ultimately granted Wiggins’s “claim stem[ming]
from counsel’s decision to limit the scope of their investiga-
tion into potential mitigating evidence.” Id. at 521. Defense
counsel’s mitigation investigation had been limited to two
items: (1) a written presentence investigation (“PSI”) report
containing a one-page account of Wiggins’s personal history
noting “misery as a youth”; and (2) Baltimore Department of
Social Services (“DSS”) records documenting Wiggins’s
placements in the foster care system. Id. at 523-24. The Court
concluded that “[c]ounsel’s decision not to expand their
investigation beyond the PSI and the DSS records fell short
of the professional standards that prevailed in Maryland in
1989” because “counsel abandoned their investigation of peti-
tioner’s background after having acquired only rudimentary
knowledge of his history from a narrow set of sources.” Id. at
524. The Court noted that “[c]ounsel’s conduct [ ] fell short
of the standards for capital defense work articulated by the
American Bar Association (ABA) — standards to which [the
                        EARP v. STOKES                    12723
Court] long [has] referred as guides to determining what is
reasonable.” Id. (internal quotation marks and citations omit-
ted). The relevant ABA guidelines state that counsel in capital
cases should consider the following information about a peti-
tioner: medical history, educational history, employment and
training history, family and social history, prior adult and
juvenile correctional experience, and religious and cultural
influences. Id. (citing ABA Guidelines for the Appointment
and Performance of Counsel in Death Penalty Cases § 11.8.6,
p. 133).

   In addition to finding that the investigation should have
been more expansive and probing as a general matter, the
Wiggins Court further found that the investigation was “un-
reasonable in light of what counsel actually discovered” in the
course of their limited investigation. Id. at 525; see also
Stankewitz, 365 F.3d at 722. Specifically, the Court found that
the DSS report should have tipped off counsel and triggered
more robust investigation because it mentioned that Wig-
gins’s mother was an alcoholic, that Wiggins and his siblings
went without food, that Wiggins suffered emotional trouble,
and that Wiggins experienced trouble in school. Wiggins, 539
U.S. at 524. In light of this information, the Court found that
counsel uncovered no evidence in the course of the investiga-
tion that would indicate that “further investigation would have
been fruitless.” Id.

   The Supreme Court has conveyed a clear, and repeated,
message about counsel’s sacrosanct duty to conduct a full and
complete mitigation investigation before making tactical deci-
sions, even in cases involving similarly egregious circum-
stances. Based on this mandate, we hold that the district court
abused its discretion in denying Earp’s request for an eviden-
tiary hearing and remand for such a hearing. At the proceed-
ing, the Warden will have the opportunity to challenge Earp’s
allegations and the evidence rallied to support his claim. Earp
will also have the opportunity to further substantiate his alle-
12724                    EARP v. STOKES
gations. In other words, Earp must be given a full and fair
hearing on his ineffective assistance of counsel claim.

   [10] Although counsel clearly has a duty to conduct a full
and complete mitigation investigation, we find it difficult to
know where a habeas court may draw the line in deciding
how far defense counsel must go in conducting the mitigation
investigation for the penalty phase of a capital case. We think
the jurisprudential principle to be gleaned from Wiggins is
that, although counsel is not required “to investigate every
conceivable line of mitigating evidence no matter how
unlikely the effort would be to assist the defendant at sentenc-
ing[,]” id. at 533, they are in no position to decide, as a tacti-
cal matter, not to present mitigating evidence or not to
investigate further just because they have some information
about their client’s background, id. at 527. Moreover, Wiggins
also establishes that the presence of certain elements in a capi-
tal defendant’s background, such as a family history of alco-
holism, abuse, and emotional problems, triggers a duty to
conduct further inquiry before choosing to cease investigat-
ing. Id. at 525. How far they must go is obviously heavily
fact-dependent and cannot be ascertained here without devel-
oping a more complete evidentiary record on remand.

                                2

   [11] Earp’s claim invokes the essential issue in Wiggins:
whether counsel’s decision, based on a limited amount of
information, to cease further investigation into mitigating evi-
dence deprived Earp of his constitutional right to effective
assistance of counsel. As stated in Wiggins, the issue in Earp’s
case is not whether Dell should have presented certain mitiga-
tion evidence during the penalty phase, but whether she
should have investigated further before deciding to cease
investigating. “[W]e focus on whether the investigation sup-
porting counsel’s decision . . . was itself reasonable.” Id. at
523. We conclude that an evidentiary hearing is required
because Earp’s allegations are sufficient to trigger the need
                         EARP v. STOKES                     12725
for a hearing on whether Dell’s investigation was unreason-
able in light of the evidence she uncovered.

   During the penalty phase, attorney Dell’s mitigation pre-
sentation consisted of testimony from five witnesses. Earp’s
aunt and mother testified about his family background and
childhood: his father’s alcoholism, physical abuse of Earp’s
mother, and emotional abuse of Earp and his siblings; his
stepfather’s alcoholism, violence, and abuse of Earp, his
mother, and his siblings; Earp’s father’s suicide and its effect
on Earp; and Earp’s juvenile history, including time spent in
juvenile detention. Earp, 978 P.2d at 30-31. Gloria Hall, a
juvenile facility cook from Earp’s time in CYA detention,
opined that Earp committed crimes as a juvenile because of
his family situation, and stated that Earp “was awarded honor
status” at the facility. Id. at 30. Virginia MacNair testified that
she and Earp’s son visited him in jail, and that Earp sent them
letters and pictures. Id. James Park, the former associate war-
den at San Quentin, testified that he thought Earp “would
pose no danger in a high security prison” and that he would
adjust well to confinement. Id. Although Dell presented this
mitigation evidence, Earp contends that her investigation was
still insufficient in light of the evidence she uncovered.

   Earp claims that his penalty phase presentation would have
“materially benefitted” from evidence and testimony about his
violent family and social background, substance abuse, men-
tal illness, history of emotional problems, and brain injury.
See Stankewitz, 365 F.3d at 721-22 (finding that petitioner’s
penalty phase representation would have benefitted from
information about the petitioner’s background, history of
mental illness, and substance abuse problems). In his motion
for an evidentiary hearing on this claim, Earp stated that he
would present: (1) testimony of counsel as to her failure to
obtain and present family and personal background; (2) evi-
dence as to family and personal history obtained by habeas
counsel, including records of emotional problems and possi-
ble psychological and neurological problems stemming from
12726                      EARP v. STOKES
early childhood, medical evaluations evincing organic brain
damage which may have exacerbated Earp’s behavioral prob-
lems, as well as testimony from family and friends regarding
Earp’s ongoing substance abuse; and (3) expert testimony
regarding prejudice.

   In support of his claim, Earp presented the district court
with: declarations from family members providing additional
details about his background; declarations from family mem-
bers, associates, and a CYA counselor discussing his history
of substance abuse; declarations regarding Earp’s time spent
in CYA custody; an expert report finding that Earp’s psycho-
social history and neuropsychological functioning prior to,
during, and after commission of the crime may have presented
a viable defense because Earp’s test results and records were
“consistent with organic damage[ ] [caused] by traumatic
brain injury”; and an expert report as to counsel’s failure to
render effective representation.

   If true, the facts alleged may well paint a materially differ-
ent picture of Earp’s background and culpability, the very
things considered relevant and vital to a competent mitigation
presentation. See, e.g., Douglas v. Woodford, 316 F.3d 1079,
1090 (9th Cir. 2003). First, the declarations set forth a more
detailed view of Earp’s family background. For instance, the
declarations allege details of Earp’s father’s (Don Earp) alco-
holic binges, sometimes leading to police dispatches and often
resulting in serious beatings of Earp’s mother.13 They also
outline Don Earp’s slide from alcoholism into suicide after
being severely beaten himself, discussing how his violence
toward the family and “uncontrollable rages” intensified. The
declarations also set forth an account of Ricky Earp’s life
after his father’s suicide spent in the company of a similarly
abusive and alcoholic stepfather in a house where “finances,
and indeed even food and shelter were inconsistent.” The dec-
  13
    Some of the declarations state that Earp and his siblings were occa-
sionally beaten during these binges as well.
                        EARP v. STOKES                    12727
larations detail the trauma that his father’s suicide caused
Earp. See id. at 1087-89 (finding deficient counsel due, in
part, to failure to investigate and present additional evidence
of petitioner’s family background and “difficult childhood”);
see also Wiggins, 539 U.S. at 525 (finding ineffective assis-
tance for failure to investigate petitioner’s background involv-
ing abuse, alcoholism, neglect, and emotional trouble).

   Second, the declarations from friends and family outline a
history of substance abuse that the state court did not address
and that the district court found to be unimportant. The decla-
rations state that Earp’s drug abuse began with smoking mari-
juana when he was twelve or thirteen years old, and that he
later used other illegal drugs on a regular basis, including
methamphetamine, cannabinol, LSD, and other hallucinogen-
ics. The declarants also note that Earp consumed large quanti-
ties of alcohol during his teen years, sometimes selling
marijuana to adults in exchange for the purchase of alcohol.
See Lambright v. Stewart, 241 F.3d 1201, 1207 (9th Cir.
2001) (determining that counsel’s failure to obtain a psychiat-
ric evaluation of the petitioner where he had a history of “ex-
tensive drug abuse,” among other things, constituted deficient
performance and warranted remand for an evidentiary hear-
ing).

   Finally, the declarations, records, and reports regarding
Earp’s emotional and neurological history allege additional
mitigation grounds. Earp’s school records, including progress
reports, psychological evaluations, and testing results, contain
details that should have caused counsel to investigate further.
Specifically, a psychological report conducted after repeated
behavioral problems stated that Earp “should be considered
for at least partial Educationally Handicapped placement” and
that “[s]uch placement would be on an emotional disturbance
basis.” The report goes on to note that “[a]lternate ways to
deal with disturbing behavior and emotionally charged feel-
ings should be explored, as well as the desirability of outside
agency counseling.” The report also discusses Earp’s test
12728                       EARP v. STOKES
results and observations, finding that Earp was “very trou-
bled,” suffered from “a great deal of anxiety,” and was “hav-
ing trouble coping emotionally.”

   The testing and observations also revealed a “lack of ade-
quate control.” A later report, documenting a psychiatrist-
parent conference regarding Earp’s “obvious emotional dis-
turbance,” also dealt with Earp’s trauma resulting from his
father’s suicide.14 Earp alleges that these problems continued,
as evidenced by a CYA intake report noting that Earp “has
experienced psychosocial turmoil” and “witnessed alcohol-
ism, physical brutality, domination, inconsistent discipline,
and marital discord followed by divorce and a broken home.”
See Ainsworth v. Woodford, 268 F.3d 868, 875-76 (9th Cir.
2001) (finding ineffective assistance where counsel failed to
investigate and present mitigation evidence regarding, inter
alia, petitioner’s history of emotional problems dating back to
childhood).

   Earp asserts that the emotional problems that he alleges to
have suffered throughout his youth and into adulthood were
exacerbated and augmented by a head injury that he suffered
in a motorcycle accident at age eight or nine, resulting in
organic brain damage. Expert Dr. Ines Monguio conducted
neuropsychological testing of Earp, finding that his function-
ing is “consistent with the presence of organic damage.”
Monguio also determined that discrepancies in Earp’s verbal
functions were consistent with brain damage. The expert con-
cluded that Earp displayed the “consequences of the brain
trauma” suffered in the motorcycle accident, as well as “gen-
eralized damage probably incurred through consistent and
extreme” substance abuse. Monguio concluded that the testing
results and background data were “consistent with organic
damage[ ] [caused] by traumatic brain injury[,]” and noted
that a “person diagnosed with this type of damage display[s],
  14
    A follow-up psychiatrist-parent conference report noted that “the situ-
ation has not improved” and had, in fact, possibly worsened.
                           EARP v. STOKES                       12729
among other symptoms, impulsive behavior, problems with
self-monitoring (regulating behavior), and poor judgment.”
See Douglas, 316 F.3d at 1086 (finding ineffective assistance
of counsel for failure to investigate and present mitigation
evidence where petitioner suffered from “possible organic
impairment” and test results revealed “some level of pre-
existing neurological deficit”) (internal quotation marks omit-
ted).

                                  3

   [12] We hold that under Williams and Wiggins Earp has
met his burden of showing a colorable claim sufficient to trig-
ger entitlement to an evidentiary hearing. He has adequately
alleged that counsel unreasonably curtailed investigation into
mitigating evidence, even after being presented with informa-
tion warranting and triggering a duty to look further. In her
declaration, attorney Dell stated the following: that she did
not present any evidence that “was not entirely consistent
with [Earp’s] claim of innocence”; that her main penalty
phase theme was “lingering doubt”; that she was solely
responsible for the investigation and preparation of Earp’s
penalty phase presentation; that she obtained the services of,
and relied on completely, defense investigator Sheryl Duvall;
that she did not direct Duvall’s investigation or instruct her to
investigate specific areas; that the defense investigator
obtained Earp’s school and medical records; that Dell did not
collect, or instruct to be collected, evidence concerning the
conditions of confinement in the CYA at the time of Earp’s
detention; and finally, that she knew of Earp’s head injury and
history of substance abuse, but did not seek a neurological or
mental health evaluation.15

  The district court determined, and the Warden now argues,
  15
    Whether her proffered evidence will withstand the crucible of an
adversary proceeding and cross-examination for possible bias remains to
be seen.
12730                   EARP v. STOKES
that counsel’s mitigation case represented a tactical decision
entitled to deference. However, deference is only owed to
strategic decisions reached after “thorough investigation of
law and facts relevant to plausible options[.]” Strickland, 466
U.S. at 690. We do not see how such a conclusion may be
made on this record without a factual hearing. Earp alleges
that his counsel failed to obtain a mental health, neurological,
or psychological evaluation of Earp, despite being alerted to
the following evidence about Earp’s background: (1) that he
had both a personal and a family history of substance abuse;
(2) that his family had a history of alcoholism, mental illness,
suicide, and physical and emotional abuse; (3) that Earp’s
father and stepfather were abusive; (4) that Earp’s mother was
physically abused; (5) that Earp had a history of emotional
problems; and (6) that Earp had suffered a head injury.

   [13] If proven to be true during future evidentiary hearings,
this alleged history of substance abuse, emotional problems,
and organic brain damage is the very sort of mitigating evi-
dence that “might well have influenced the jury’s appraisal of
[Earp’s] moral culpability.” Williams, 529 U.S. at 398; see
also Douglas, 316 F.3d at 1090 (“Evidence regarding social
background and mental health is significant, as there is a
‘belief, long held by this society, that defendants who commit
criminal acts that are attributable to a disadvantaged back-
ground or to emotional or mental problems, may be less cul-
pable than defendants who have no such excuse.’ ”) (quoting
Boyde v. California, 494 U.S. 370, 382 (1990)); Allen v.
Woodford, 395 F.3d 979, 1000 (9th Cir. 2005) (“Defense
counsel’s use of mitigation evidence to complete, deepen, or
contextualize the picture of the defendant presented by the
prosecution can be crucial to persuading jurors that the life of
a capital defendant is worth saving.”) (citations omitted).

   If proven, Earp’s allegations could establish a colorable
claim that counsel’s failure to investigate mitigating evidence,
“despite tantalizing indications in the record, as in Wiggins,
that would lead a reasonable attorney to investigate further,”
                        EARP v. STOKES                    12731
deprived Earp of his constitutionally guaranteed right to effec-
tive representation. Stankewitz, 365 F.3d at 720 (internal quo-
tation marks and citation omitted). We emphasize that the
ultimate determination must be made in the first instance by
the fact-finder at the hearing. We offer no opinion on the mer-
its of Earp’s claim here.

                               4

   But even if Earp has established a colorable claim of inef-
fective assistance for failure to conduct a competent mitiga-
tion investigation, he must also present a colorable claim that
counsel’s deficient performance prejudiced him. Wiggins, 539
U.S. at 521; see also Stankewitz, 365 F.3d at 722-23. “In
assessing prejudice, [the court] reweigh[s] the evidence in
aggravation against the totality of available mitigating evi-
dence.” Stankewitz, 365 F.3d at 723 (emphasis added) (quot-
ing Wiggins, 539 U.S. at 534). The totality of the available
evidence includes “both that adduced at trial, and the evidence
adduced in the habeas proceeding[s].” Wiggins, 539 U.S. at
536 (quoting Williams, 529 U.S. at 397-98).

   Earp has alleged that the testimony presented at the penalty
phase did not fully encompass the degree of violence, abuse,
and alcoholism that he claims to have suffered during his
formative years. It appears that the jury in this case was not
presented with the evidence that Earp alleges regarding his
history of substance abuse beginning at age twelve, his
organic brain damage and its attendant effects resulting from
his childhood head injury at age eight or nine, or his history
of emotional problems. While Earp’s life history is not as “ex-
cruciating” as that of defendants in other cases, it may well be
that, after conducting the hearing on remand, the habeas court
could conclude that, “[h]ad the jury been able to place
[Earp’s] life history on the mitigating side of the scale, there
is a reasonable probability that at least one juror would have
struck a different balance.” Wiggins, 539 U.S. at 537 (noting,
further, that Wiggins did “not have a record of violent con-
12732                   EARP v. STOKES
duct” that the prosecution could have introduced to offset the
omitted mitigating evidence).

   During the prosecution’s penalty phase of the trial, the
aggravation presentation consisted of Earp’s prior felony con-
viction for burglary. Earp, 978 P.2d at 30; see also Mayfield
v. Woodford, 270 F.3d 915, 933 (Gould, J., concurring) (not-
ing that, for purposes of prejudice, it is relevant to consider
that the defendant did not have “an extensive history involv-
ing major crimes or violence”). In finding no prejudice, the
district court determined that any omitted mitigation evidence
would not have made a difference to even a single reasonable
juror because the nature of Earp’s crime was so egregious.

   The aggravating circumstances of this case are indeed hei-
nous. However, as we have previously noted, “the Supreme
Court has made clear that counsel’s failure to present mitigat-
ing evidence can be prejudicial even when the defendant’s
actions are egregious.” Stankewitz, 365 F.3d at 723-24 (dis-
cussing Williams, 529 U.S. at 368, 398-99 (noting that, among
his other crimes, Williams confessed to “brutally assault[ing]
an elderly woman leaving her in a vegetative state” in her
home, yet still finding that the mitigating evidence that coun-
sel failed to investigate could have tipped the balance for at
least one juror) (internal quotation marks omitted)); see also
Mak v. Blodgett, 970 F.2d 614, 620-22 (9th Cir. 1992) (find-
ing prejudice despite the presence of exceedingly horrific cir-
cumstances of the crime in which the defendant slaughtered
thirteen people in the course of one night to eliminate all wit-
nesses to an armed robbery).

   [14] Given that the circumstances of Earp’s crime consti-
tuted the vast majority of the aggravation case, prejudice is
“especially likely.” Lambright, 241 F.3d at 1208 (noting that
“[p]rejudice is especially likely where, as here, this is not a
case in which a death sentence was inevitable because of the
enormity of the aggravating circumstances”) (internal quota-
tion marks and citation omitted); cf. Allen, 395 F.3d at 1009
                         EARP v. STOKES                    12733
(finding no prejudice, despite ineffective assistance, because
of the overwhelming evidence in aggravation consisting, in
part, of a “long history of orchestrating and committing vio-
lent robberies and burglaries” and plotting the murder of mul-
tiple individuals who testified against the defendant on an
earlier murder charge). Accordingly, we hold that Earp’s alle-
gations are sufficient to require an evidentiary hearing
because, if true, they could establish that he suffered prejudice
from counsel’s deficient mitigation investigation and presen-
tation.

                               V

   Earp’s second Sixth Amendment claim is that he was
deprived of effective assistance of counsel because his inti-
mate relationship with Dell created a conflict of interest
between Dell’s duties as counsel and her personal interests in
the relationship. We affirm the denial of habeas relief on this
claim because the state court finding of no conflict was nei-
ther contrary to, nor an unreasonable application of, clearly
established federal law.

                               A

   On April 23, 1991, Adrienne Dell was appointed as Earp’s
second counsel. Dell met frequently with Earp, giving him her
home phone number and speaking with him regularly in order
to build trust and rapport. During the course of her representa-
tion, Dell developed romantic feelings for Earp.

   The conversations between Earp and Dell reflected this
sentiment and started to broach more personal matters,
although only after discussing necessary case-related issues.
Dell sent Earp pictures of herself and dressed provocatively
for her visits to Earp. She also disrobed for him and engaged
in “intimate relations” with Earp during their visits. In addi-
tion, Dell gave him a religious medallion “to signify her feel-
ings for him,” picking this type of item because she knew that
12734                         EARP v. STOKES
the rules of confinement would allow for him to keep it, given
its religious nature. During the trial itself, Earp and Dell
passed personal notes and winked to each other.

   After the return of the guilty verdict, Dell confessed her
love to Earp in the holding cell and he reciprocated. From
then on, Dell and Earp shared a “strong emotional attach-
ment,” which culminated in their marriage after Earp was
transferred to death row. Dell and Earp were married from
October 7, 1993, until December 27, 2000.

   This issue was first raised in Earp’s state petition for writ
of habeas corpus and was summarily denied on the merits.
Earp reiterated this claim in his federal habeas petition. The
defense argued that, because of the relationship between Dell
and Earp, Dell: (1) failed to present any shaken baby syn-
drome evidence; (2) gave Earp too much control over his
defense; and (3) failed to present substantial mitigation evi-
dence of which she was aware. The district court held an evi-
dentiary hearing on the conflict claim and bifurcated the
inquiry, instructing counsel to only present evidence of “ac-
tual conflict,” and barring the defense from presenting any
evidence relating to whether the representation was adversely
affected by the alleged conflict.16

  At the close of the evidentiary hearing, the district court
propounded that “[b]eing in love is not a conflict,” and con-
   16
      Earp also argues that the district court’s bifurcation of the evidentiary
hearing was improper because actual conflict cannot be determined with-
out analyzing whether there was an adverse effect on representation.
While the Supreme Court in Mickens v. Taylor, 535 U.S. 162, 171-73
(2002), makes clear that the question of actual conflict is not properly ana-
lyzed as two separate inquiries, we affirm the district court’s denial of the
claim on summary judgment because, even assuming the facts alleged to
be true, the state court decision did not contravene Supreme Court prece-
dent. See supra, § V.C; see also Lambert, 393 F.3d at 965 (noting that this
court can affirm the district court decision on any ground supported by the
record).
                            EARP v. STOKES                        12735
cluded that Dell felt she was acting in Earp’s best interest. In
its order denying relief on the conflict claim, the district court
compared Dell’s situation to every lawyer’s conflict between
maintaining a personal life and a professional life: “such bal-
ancing is done by every lawyer who works past the time their
spouse goes home or school lets out.” The district court ulti-
mately concluded that, because there was no actual conflict,
it was unnecessary to examine whether there was any adverse
impact due to purported conflict.

   On appeal, Earp argues that Dell labored under an actual
conflict, relying primarily on our circuit’s case law addressing
situations where a lawyer’s personal interests conflict with the
defendant’s interest,17 as well as various state supreme court
disciplinary proceedings stemming from unethical lawyer-
client sexual relationships.18 Most of these cases involve pre-
AEDPA petitions, many of which do not involve habeas pro-
ceedings, and all of which were decided before the Supreme
Court issued Mickens v. Taylor, 535 U.S. 162, 166 (2002).
For the reasons explained below, we hold that Earp’s claim
fails, and that the district court properly denied this claim for
relief.

                                   B

   Whether counsel and client had conflicting interests is a
mixed question of law and fact which we review de novo.
Williams, 384 F.3d at 586; see also Bragg v. Galaza, 242 F.3d
1082, 1086, amended by 253 F.3d 1150 (9th Cir. 2001). We
also review de novo the district court’s summary judgment
decision. Davis, 384 F.3d at 638. Section 2254(d)(1) of
U.S.C. Title 28 applies to questions of law and mixed ques-
tions of law and fact. Id. at 637. A decision is “contrary to”
  17
     E.g., United States v. Hearst, 638 F.2d 1190 (9th Cir. 1980); United
States v. Baker, 256 F.3d 855 (9th Cir. 2001).
  18
     E.g., In re Gore, 752 So.2d 853 (La. 2000); In re Grimm, 674 N.E.2d
551 (Ind. 1996); People v. Boyer, 934 P.2d 1361 (Colo. 1997).
12736                   EARP v. STOKES
federal law when the state court applies a rule of law different
from that set forth in the holdings of Supreme Court precedent
or when the state court makes a contrary determination on
“materially indistinguishable” facts. Williams, 529 U.S. at
405-06. An “unreasonable application” of federal law occurs
when a state court’s application of Supreme Court precedent
to the facts of a petitioner’s case is “objectively unreason-
able.” Id. at 409. “[A] federal habeas court may not issue the
writ simply because that court concludes in its independent
judgment that the relevant state-court decision applied clearly
established federal law erroneously or incorrectly.” Id. at 411.

   Clearly established federal law “as determined by the
Supreme Court,” § 2254(d)(1), “ ‘refers to the holdings, as
opposed to the dicta of [the Supreme Court’s] decisions as of
the time of the relevant state-court decision.’ ” Lambert, 393
F.3d at 974 (quoting Lockyer, 538 U.S. at 71-72). Circuit
court precedent is relevant only to the extent that it clarifies
what constitutes clearly established law. Casey v. Moore, 386
F.3d 896, 907 (9th Cir. 2004); see also Clark v. Murphy, 331
F.3d 1062, 1069 (9th Cir. 2003), cert. denied, 540 U.S. 968
(2003); Duhaime v. Ducharme, 200 F.3d 597, 602-03 (9th
Cir. 2000) (Ninth Circuit precedent derived from an extension
of a Supreme Court decision is not “clearly established fed-
eral law as determined by the Supreme Court”).

                               C

   [15] While ineffective assistance of counsel claims gener-
ally require the petitioner to show deficient representation and
prejudice, we “forgo individual inquiry into whether counsel’s
inadequate performance undermined the reliability of the ver-
dict” in instances “where assistance of counsel has been
denied entirely or during a critical stage of the proceeding.”
Mickens, 535 U.S. at 166. Circumstances of such magnitude
may “arise when the defendant’s attorney actively represented
conflicting interests.” Id. at 166; see also Cuyler v. Sullivan,
446 U.S. 335, 348 (1980). In order to establish a Sixth
                             EARP v. STOKES                          12737
Amendment violation under the Sullivan exception, the defen-
dant must demonstrate that “an actual conflict of interest
adversely affected his lawyer’s performance.” Sullivan, 446
U.S. at 348. As clarified in Mickens, an actual conflict is not
“something separate and apart from adverse effect.” 535 U.S.
at 172 n.5. Rather, “[a]n ‘actual conflict,’ for Sixth Amend-
ment purposes, is a conflict of interest that adversely affects
counsel’s performance.” Id.

   The Supreme Court’s recent decision in Mickens proves
determinative in the instant appeal. In Mickens, the Supreme
Court dealt with a habeas claim in a capital case alleging inef-
fective assistance where counsel for the defendant also repre-
sented the victim, who was a defendant in an unrelated
juvenile case. Id. at 164-65. After being informed that the vic-
tim was deceased, the trial judge dismissed the juvenile
charges against him. Id. The same trial judge appointed coun-
sel in the defendant’s case. Id. at 165. The precise issue facing
the Court was “what a defendant must show in order to dem-
onstrate a Sixth Amendment violation where the trial court
fails to inquire into a potential conflict of interest about which
it knew or reasonably should have known.” Id. at 164.

   In answering this query, the Mickens Court clarified its
conflict precedent and restated the parameters of its applica-
tion. First, the Court discussed three seminal Supreme Court
conflict cases: Holloway v. Arkansas, 435 U.S. 475 (1978);19
  19
     In Holloway, defense counsel representing three codefendants with
diverging and potentially conflicting interests moved for the appointment
of separate counsel. 435 U.S. at 478-80. The Supreme Court noted that
counsel in this situation is effectively gagged from properly representing
any one of the defendants, and that it is inherently difficult to measure the
degree of harm caused by such conflicts. Id. at 489-90. The Court found
that this type of conflict undermines the fairness and efficacy of the adver-
sarial process, and that automatic reversal was necessary where defense
counsel’s objection was denied by the trial court, unless the trial court
concludes that there is no conflict. Id. at 488.
12738                        EARP v. STOKES
Sullivan, 446 U.S. at 346-49;20 and Wood v. Georgia, 450
U.S. 261 (1981).21

   After surveying precedent, the Mickens Court added an
entire section to address the limited scope of its holding, and
to explicitly cabin its conflict jurisprudence despite its expan-
sive application by lower courts. 535 U.S. at 174-76. The
Court noted that circuit courts “have applied Sullivan
‘unblinkingly’ to ‘all kinds of alleged attorney ethical con-
flicts,’ ” invoking it in cases involving interests of former cli-
ents, interests implicating counsel’s personal or financial
interest, interests inherent in romantic relationships with
opposing counsel, and interests implicated by counsel’s future
or present employment with opposing counsel. Id. at 174
(citation omitted).22 While acknowledging this expansion, the
   20
      In Sullivan, the Supreme Court addressed the issue of multiple repre-
sentation where the trial court does not and reasonably should not know
of the conflict. 446 U.S. at 345-50. The Sullivan Court noted that Hol-
loway recognized that “a lawyer forced to represent codefendants whose
interests conflict cannot provide the adequate legal assistance required by
the Sixth Amendment.” Id. at 345 (citing Holloway, 435 U.S. at 481-82).
The Sullivan Court further developed the joint representation conflict stan-
dard, stating that, “[i]n order to establish a violation of the Sixth Amend-
ment, a defendant who raises no objection at trial must demonstrate that
an actual conflict of interest adversely affected his lawyer’s performance”
and that a defendant who makes such a showing is not required to show
prejudice in order to obtain relief. Id. at 348, 349-50.
   21
      In Wood, the Court remanded for proceedings to determine whether
there was an actual conflict where the defendants’ lawyer was being paid
by the defendants’ employer. 450 U.S. at 269-72 (employer owned a busi-
ness purveying obscene material, and the defendants had been convicted
in connection with the business). The defendants’ employer had been pay-
ing the defendants’ fines, imposed after their conviction for distributing
obscenity. Id. at 276. The Court determined that remand was necessary
because “petitioners were represented by their employer’s lawyer, who
may not have pursued their interests single-mindedly.” Id. at 271-72.
   22
      Earp argues that, despite Mickens, circuit courts have long applied the
Sullivan conflict framework to a wide variety of conflicts in addition to the
traditional concurrent representation application. See, e.g., Mannhalt v.
                             EARP v. STOKES                          12739
Court cautioned that its own conflict jurisprudence had not
yet reached beyond joint representation: “the language of Sul-
livan itself does not clearly establish, or indeed even support,
such expansive application . . . . Both Sullivan itself [ ] and
Holloway [ ] stressed the high probability of prejudice arising
from multiple concurrent representation, and the difficulty of
proving that prejudice. Not all attorney conflicts present com-
parable difficulties.” Id. at 175 (internal citations omitted).
The Court propounded that the conflict inquiry does not, and
should not, entail weighing of professional ethical duties, and
that the Sullivan exception is not intended to enforce and
encourage compliance with codes of conduct:

     This is not to suggest that one ethical duty is more
     or less important than another. The purpose of our
     Holloway and Sullivan exceptions from the ordinary
     requirements of Strickland, however, is not to
     enforce the Canons of Legal Ethics, but to apply
     needed prophylaxis in situations where Strickland
     itself is evidently inadequate to assure vindication of
     the defendant’s Sixth Amendment right to counsel.

Id. at 176.

Reed, 847 F.2d 576, 580-81 (1988) (pre-AEDPA habeas case finding that
Sullivan applies when an attorney is accused of similar crimes for which
his client is being prosecuted); Garcia v. Bunnell, 33 F.3d 1193, 1196-98
(9th Cir. 1994) (pre-AEDPA habeas case finding that, although the “vast
bulk of the caselaw in the attorney conflict area involves alleged conflicts
arising out of representation of multiple defendants by a single attorney
who may not be able simultaneously to serve optimally the interests of
each,” Sullivan also applies “to conflicts between a defendant’s and the
attorney’s own personal interests”); see also Winkler v. Keane, 7 F.3d 304,
307 (2d Cir. 1993) (citing other sister circuit cases expanding application
of the Sullivan standard). This line of argument, however, is futile post-
AEDPA; only Supreme Court holdings are binding on state courts. See
Lambert, 393 F.3d at 974 (“only the Supreme Court’s holdings are binding
on the state courts and only those holdings need be reasonably applied”)
(quoting Clark v. Murphy, 331 F.3d 1062, 1069 (2003)).
12740                   EARP v. STOKES
   [16] The Mickens Court specifically and explicitly con-
cluded that Sullivan was limited to joint representation, and
that any extension of Sullivan outside of the joint representa-
tion context remained, “as far as the jurisprudence of [the
Supreme Court was] concerned, an open question.” Id.

                              D.

   [17] The Supreme Court has never held that the Sullivan
exception applies to conflicts stemming from intimate rela-
tions with clients. See Lambert, 393 F.3d at 986 (noting that
Supreme Court precedent is limited to conflicts involving
joint representation); see also Smith v. Hofbauer, 312 F.3d
809, 815-17 (6th Cir. 2002) (finding that the Sullivan line of
Supreme Court precedent only apply, for AEDPA purposes,
to cases involving joint representation; noting that “[b]ecause
the question of whether the Sullivan’s lessened standard of
proof for a claim of ineffective assistance of counsel based
upon an attorney’s conflict of interest for anything other than
joint representation remains an ‘open question’ in the juris-
prudence of the Supreme Court, and in fact was an open ques-
tion at the time Petitioner’s case was heard, Petitioner’s claim
fails because it is not based upon clearly established Supreme
Court precedent as mandated by AEDPA”) (internal citation
omitted).

                               E

   [18] While our circuit’s precedent has expanded the scope
of the Sullivan exception to apply in other contexts, and while
we strongly disapprove of Adrienne Dell’s unprofessional
behavior as reflected in her conduct at bar, the advent of
AEDPA forecloses the option of reversing a state court deter-
mination simply because it conflicts with established circuit
law. Although we would perhaps reach a different conclusion
if addressing this claim on direct review, the Supreme Court
has not spoken to this issue and has expressly limited its con-
stitutional conflicts jurisprudence. Accordingly, we hold that
                         EARP v. STOKES                    12741
the state court’s determination that the intimate relationship
between Earp and his counsel during the trial and sentencing
did not constitute a conflict of interest was neither contrary to,
nor an unreasonable application of, established federal law.

                               VI

   Earp is entitled to an evidentiary hearing on his prosecu-
torial misconduct claim involving Michael Taylor because he
has alleged facts which, if proven true, may entitle him to
relief on this claim. Earp is also entitled to an evidentiary
hearing on his ineffective assistance of counsel claim because
he has demonstrated a colorable claim that counsel’s mitiga-
tion investigation was deficient in light of the evidence
uncovered, and that he suffered prejudice thereby. We there-
fore vacate the district court’s summary judgment on these
claims and remand for an evidentiary hearing. The district
court’s decision to deny Earp’s conflict of interest claim was
neither contrary to, nor an unreasonable application of, clearly
established federal law, so we affirm that part of the district
court’s summary judgment.

 AFFIRMED in part, REVERSED in part, and
REMANDED for an evidentiary hearing.
