                 FOR PUBLICATION
 UNITED STATES COURT OF APPEALS
      FOR THE NINTH CIRCUIT

JAMES F. HORTON, II,                      No. 03-56618
             Petitioner-Appellant,
               v.                           D.C. No.
                                         CV-97-07298-MRP
DENEICE MAYLE, Warden,
                                            OPINION
            Respondent-Appellee.
                                     
       Appeal from the United States District Court
           for the Central District of California
       Mariana R. Pfaelzer, District Judge, Presiding

                Argued and Submitted
         December 7, 2004—Pasadena, California

                    Filed May 10, 2005

    Before: Betty B. Fletcher, Pamela Ann Rymer, and
             Richard A. Paez, Circuit Judges.

                 Opinion by Judge Rymer;
                  Opinion by Judge Paez;
                 Dissent by Judge Rymer




                           5065
5068                 HORTON v. MAYLE


                       COUNSEL

Michael Rubin and Dorothea K. Langsam, Altshuler, Berzon,
Nussbaum, Rubin & Demain, San Francisco, California, for
the petitioner-appellant.

Lance E. Winters, Supervising Deputy Attorney General, Los
Angeles, California, for the respondent-appellee.
                       HORTON v. MAYLE                     5069
                          OPINION

RYMER, Circuit Judge:

   James F. Horton, II, a California state prisoner, appeals
from the denial of his 28 U.S.C. § 2254 petition for a writ of
habeas corpus. We agree with the magistrate judge’s analysis,
adopted by the district court, and affirm on all issues except
for Horton’s claim that his rights under Brady v. Maryland,
373 U.S. 83 (1963), were violated. As to that claim, the court
reverses and remands in a separate opinion authored by Judge
Paez.

                               I

   Shortly after 2:30 p.m. on Monday, October 11, 1982,
paramedics responded to a call by Carolyn Ebel, the girlfriend
of Herschel “Lobo” Bowser, who lived in an apartment on
Artesia Boulevard in Los Angeles. They found Bowser lying
unconscious on the floor, his head bleeding severely. A ham-
mer was within a foot of the body near a pool of blood.
Bowser died at the hospital later that day, having suffered
twelve blunt injuries to the head and a fractured skull. The
blows were consistent with force applied by the hammer. No
fingerprints, blood, or DNA were found at the scene except
for one print taken from a tool box, which matched the prints
of the victim.

   Ebel had left a wallet containing over $100 and the changer
from her catering truck in a money bag at Bowser’s apartment
and testified that Bowser, who was a drug dealer, kept a large
amount of cash in the apartment. She saw Bowser in bed
asleep about 9:30 in the morning when she went to pick up
a paycheck; around noon, she got a call from Tracy Crisp,
who lived in the building, saying that Crisp had been unable
to reach Bowser on the telephone. As a result of that call, Ebel
returned to Bowser’s apartment around 2:30 p.m.; the top lock
was unlocked and when she opened the door as far as she
5070                   HORTON v. MAYLE
could (Bowser was on the floor with his legs by the door), she
saw that the living room was in shambles. Empty bags were
strewn all over, and her wallet as well as the money bag with
$40-70 and rolled change was gone. Ebel testified that
Bowser kept his cocaine in a butter dish in a cupboard next
to the stove in the kitchen, which is where he would take cus-
tomers to negotiate sales. He stored the cocaine in ziploc plas-
tic bags — two of powdered cocaine and one of rock cocaine
— and one of the bags was marked with black “X’s.” Ebel
noticed when she went into the kitchen after the crime that the
cover of the butter container was off and the three bags of
cocaine that had been in it were gone.

   Horton was a customer of Bowser’s whom Ebel had seen
at Bowser’s apartment. In October 1982, Horton lived at the
Shangri Lodge, which was managed by Willie Dorn. Michael
Graham also lived there and he and Horton did odd jobs for
Dorn. One day in October Horton asked Graham for a ham-
mer that belonged to Dorn, which Graham gave him. Graham
could not identify the hammer found near Bowser, but Dorn
did. He testified that he had owned this hammer for twelve
years, that Graham had been using it in October, and that he
hadn’t seen it for about a week before October 10. At least
one of the paint specks on the hammer was similar to the paint
used on the Shangri Lodge buildings.

   On the morning of October 10, Horton told Dorn that there
was something he had to do and, if it worked out, Horton
would be moving out the next day. The next day, around 9
o’clock, Dorn saw Horton leave in his car with James
(“Doonie”) Cunnigan and Anthony Wilson. A few days later,
Horton telephoned Dorn and asked if the police had been
looking for him. He called back with the question several
more times. Horton told Dorn to tell Graham that if anybody
asked Graham whether he had given Horton anything to tell
them “no.”

  Donald “Foo” McLaurin was the prosecution’s principal
witness. The following is taken from his testimony. McLaurin
                      HORTON v. MAYLE                    5071
had known Horton since 1979 or 1980. They used drugs
together. Horton had taken McLaurin to Bowser’s apartment
building to buy cocaine, but McLaurin testified that he never
went inside. Horton told McLaurin that he bought the cocaine
from someone named “Lo” or something like it. Bowser’s
nickname was “Lobo.”

   McLaurin testified that he, Horton, Wilson, and Horton’s
brother William went to Bowser’s building on the morning of
October 10 and that Horton came out with a bag of cocaine.
They went to Ray’s Motel where they proceeded to get high,
then went to the Shangri Lodge where they were joined by
Cunnigan and consumed more cocaine. According to
McLaurin, Horton began to discuss a plan to rob his dealer,
said that he could use a pipe to “slug him a few times,” and
indicated he knew his dealer kept cocaine in one of the
kitchen cabinets. McLaurin agreed to drive Horton to the
dealer’s apartment, but instead left with his girlfriend.

   About 1 p.m. on the 11th, Horton called McLaurin at work
and asked McLaurin to meet him at Ray’s Motel. Horton
stated that he “did the number he was talking about last
night.” Horton, Doonie, and Anthony were at Ray’s when
McLaurin got there. McLaurin saw three bags of cocaine, two
with a powdered substance and one with cocaine rocks. There
were black “X’s” on one of the bags. McLaurin also saw a
large roll of money. They began to smoke cocaine.

   According to McLaurin, Horton said that he (Horton), Doo-
nie, and Anthony went to the apartments on Artesia. Cunni-
gan stated that “everything went down pretty smooth.” Horton
said that he walked into the apartment, the dealer turned his
back and closed the door, and Horton clubbed him on the
head with a hammer. Horton then went to the kitchen cabinet
and grabbed the cocaine. On the way back, Horton’s car over-
heated on the freeway and they left it. At Ray’s, Horton asked
McLaurin to pick it up. McLaurin and Cunnigan returned to
the car and retrieved a gym bag and a couple of bags of mari-
5072                   HORTON v. MAYLE
juana, but left the car. After McLaurin and Cunnigan returned,
the group consumed more drugs and then McLaurin drove
Horton, Doonie, and Anthony to the Greyhound bus depot.

   McLaurin’s supervisor testified that McLaurin arrived for
work on October 11 at 5:45 a.m. and left at 1 p.m. after
receiving a telephone call. Much later, in November 1984,
McLaurin was incarcerated on a probation violation and was
housed in the same module as Horton. He met with Horton’s
counsel.

   At trial, McLaurin testified that he was in jail for a proba-
tion violation based on testing positive for cocaine, that he
lied to Horton’s attorney when he talked with him because he
feared harm if other inmates knew he was a “snitch,” and that
neither the police nor the district attorney “helped him out”
with the sentencing on the probation violation. McLaurin also
admitted that he told defense counsel that he had been
untruthful about everything he had told the police. He stated
that he habitually smoked marijuana, had tried PCP, and had
smoked a lot of cocaine the night before the murder; that he
wasn’t functioning too clearly when the plan was being dis-
cussed; and that he was never charged with a crime even
though he had driven Horton to the bus depot.

   On April 1, 1985 a jury found Horton guilty of first degree
murder and robbery, Cal. Penal Code §§ 187 and 211, finding
true the special circumstance that the murder was committed
during a robbery, Cal. Penal Code § 190.2(a)(17). In a bifur-
cated proceeding the jury also found true a special circum-
stance that Horton had a prior murder conviction. Cal. Penal
Code § 190.2(a)(2). Following a penalty phase, the jury
returned a verdict of death on April 16, 1985. On December
11, 1995 the California Supreme Court reversed the prior
murder special circumstance and the death penalty verdict,
but otherwise affirmed the judgment. People v. Horton, 11
Cal.4th 1068, 906 P.2d 478 (1995). The state elected not to
                       HORTON v. MAYLE                      5073
retry the penalty phase, therefore Horton’s sentence stands at
life in prison without the possibility of parole.

   On October 17, 1989 Horton filed a petition for writ of
habeas corpus in the California Supreme Court based on his
trial by a commissioner instead of a superior court judge,
which the court denied on August 12, 1991. In re Horton, 54
Cal.3d 82, 813 P.2d 1335 (1991). He filed a second petition
for writ of habeas corpus in the California Supreme Court on
April 3, 1995, which the court denied on July 18, 1996.

   On October 2, 1997 Horton filed his first federal petition;
he filed a Second Amended Petition on March 6, 2001. The
district court denied all of Horton’s claims on the merits. The
court granted a Certificate of Appealability (COA) on four
issues that Horton pursues on appeal, and he has requested
certification on five additional claims.

                               II

   We review de novo a district court’s decision to grant or
deny a 28 U.S.C. § 2254 habeas petition. Benn v. Lambert,
283 F.3d 1040, 1051 (9th Cir. 2002). Because Horton’s peti-
tion was filed after April 24, 1996, the amendments to § 2254
under the Antiterrorism and Effective Death Penalty Act
(AEDPA) apply. Id. Under AEDPA, Horton is not eligible for
habeas relief unless the decision of the California Supreme
Court was “contrary to, or involved an unreasonable applica-
tion of, clearly established Federal law, as determined by the
Supreme Court of the United States,” or was “based on an
unreasonable determination of the facts in light of the evi-
dence presented in the State court proceeding.” 28 U.S.C.
§ 2254(d); see also Benn, 283 F.3d at 1051. A state court
decision is contrary to clearly established federal law if the
state court applies a rule that contradicts the governing law set
forth in Supreme Court cases or if the state court confronts a
set of facts that are materially indistinguishable from a deci-
sion of the Supreme Court and nevertheless arrives at a result
5074                   HORTON v. MAYLE
different from the Supreme Court precedent. Lockyer v.
Andrade, 538 U.S. 63, 73 (2003). A state court decision
involves an unreasonable application of clearly established
federal law if the state court identifies the correct governing
legal principle from the United States Supreme Court’s deci-
sions but unreasonably applies that principle to the facts of the
prisoner’s case; the state court decision must be more than
incorrect or erroneous, it must be objectively unreasonable.
Id. at 75. If a state law issue must be decided in order to
decide a federal habeas claim, the state’s construction of its
own law is binding on the federal court. Mullaney v. Wilbur,
421 U.S. 684, 691 (1975).

                               III

   [1] Horton contends that trial counsel was ineffective in
failing to impeach McLaurin with prior felony convictions,
including a conviction on August 10, 1982 for possession of
PCP with intent to sell. The California Supreme Court
rejected this claim for lack of prejudice given McLaurin’s
own testimony that revealed his extensive drug use and the
fact that he was on probation for a criminal conviction. We
agree with the district court that this is not an unreasonable
application of United States Supreme Court law as set out in
Strickland v. Washington, 466 U.S. 668, 687 (1984) (defen-
dant must show both that counsel’s performance was deficient
and that the deficient performance prejudiced the defense).
The jury knew that McLaurin had used cocaine, marijuana
and PCP, that he had a criminal history, and that he was an
admitted liar. In short, McLaurin’s credibility was so under-
mined anyway that evidence that he also had a conviction for
possession with intent to sell PCP would not have affected the
outcome.

                               IV

  [2] Horton also challenges his trial counsel’s performance
on the ground that counsel advised him not to testify based on
                           HORTON v. MAYLE                            5075
the mistaken belief that Horton’s prior murder conviction
could be used to impeach him even though the trial judge had
ruled that it was inadmissible. We agree with the district
court’s bottom line, that the Strickland standard has not been
met. Counsel’s declaration does not indicate when he told
Horton that his prior conviction might be used to impeach him
(it could have been before the trial judge’s ruling).1 Nor is
there any indication from Horton that he wanted to testify or
would have testified; he gave no such signal at trial, see, e.g.,
Dows v. Wood, 211 F.3d 480, 487 (9th Cir. 2000); United
States v. Edwards, 897 F.2d 445, 446 (9th Cir. 1990), or in the
district court. Further, there is no submission indicating what
he might have testified to. In these circumstances, and in light
of Horton’s own inculpatory conduct and statements, it would
be sheer speculation to say that the outcome would have been
different.

                                    V

   [3] Horton maintains that his constitutional right to a fair
trial was violated because his trial was conducted by a court
commissioner who lacked jurisdiction. In California, the juris-
diction of a court commissioner derives from the parties’ stip-
ulation. Cal. Const., art. VI, § 21. There was no formal
stipulation to the commissioner’s serving in this case, but
Horton and his counsel knew that the presiding judicial offi-
cer was a commissioner rather than a superior court judge.
Knowing this, they appeared and allowed the proceedings to
go forward without objection. As the California Supreme
Court explained, a valid stipulation for purposes of Califor-
nia’s constitutional provision may arise as a result of the con-
duct of the parties. In re Horton, 813 P.2d at 1339. This is
known as the “tantamount stipulation doctrine,” and the attor-
  1
    We note that the declaration reflects a strategic concern about Horton’s
taking the stand in the guilt phase with the penalty phase, including the
special circumstance prior murder conviction that had not yet been
stricken.
5076                        HORTON v. MAYLE
ney’s conduct alone is sufficient to trigger it. Id. at 1340.
Here, the supreme court found that the conduct of Horton’s
counsel was dispositive, and that Horton’s explicit authority
or waiver was not required. It also concluded that trial by a
commissioner did not offend Horton’s federal constitutional
rights because the commissioner “takes on the mantle of a
regularly appointed superior court judge in presiding over the
trial and applies all the usual rules and procedures applicable
in such a proceeding.” Id. at 1346.

   [4] We cannot say that the California Supreme Court’s
determination is contrary to clearly established federal law.
Under California law, the commissioner who presided over
Horton’s trial had jurisdiction under the tantamount stipula-
tion doctrine. Nothing more is required by the cases upon
which Horton relies, Gomez v. United States, 490 U.S. 858
(1989) and English v. United States, 42 F.3d 473 (9th Cir.
1994). Both recognize that the right to be tried by a person
with jurisdiction is a critical element of the federal constitu-
tional right to a fair trial, but that right was honored here. And
as the district court held, to the extent Article III jurispru-
dence or federal law interpreting the Federal Magistrates Act,
28 U.S.C. § 636(b)(3), is relevant, Horton’s case falls between
Gomez and Peretz v. United States, 501 U.S. 923, 936 (1991)
(finding no constitutional infirmity in the delegation of felony
trial jury selection to a magistrate judge when petitioner’s
counsel affirmatively welcomed the magistrate’s role rather
than objecting).

                                    VI

   [5] Horton’s motion to broaden the Certificate of Appeala-
bility is denied. Reasonable jurists would not find the district
court’s assessment of the claims that he wishes to pursue
debatable or wrong. Slack v. McDaniel, 529 U.S. 473, 484
(2000).2
   2
     Although we agree with the district court’s conclusion on Horton’s
appellate delay claim, we do so on the ground that he fails to make a sub-
stantial showing of the denial of a constitutional right under clearly estab-
lished Supreme Court law.
                          HORTON v. MAYLE                           5077
                                  VII

                      Opinion by Judge Paez

PAEZ, Circuit Judge:

   Horton alleges that the prosecution violated his rights under
Brady v. Maryland, 373 U.S. 83 (1963), by failing to disclose
a deal between the police and McLaurin, under which
McLaurin agreed to testify as the prosecution’s star witness in
exchange for immunity for anything he did on the weekend of
the murder. The district court denied relief on this claim with-
out making a factual finding as to the existence of a deal
between the police and McLaurin. Instead, the court con-
cluded that even assuming the alleged deal existed, evidence
of the deal was not material under Brady v. Maryland. We dis-
agree.3 We hold that the prosecution’s failure to disclose the
deal between the police and McLaurin violated Brady. Thus,
we vacate the district court’s denial of Horton’s Brady claim
and remand to the district court for further proceedings.

   [6] In criminal cases, the prosecution has a duty to disclose
all material evidence that is favorable to the accused. Brady,
373 U.S. at 87. This duty extends not only to exculpatory evi-
dence but also to “evidence that the defense might have used
to impeach the Government’s witnesses by showing bias or
interest.” United States v. Bagley, 473 U.S. 667, 676 (1985).
Evidence is material if “there is a reasonable probability that,
had the evidence been disclosed to the defense, the result of
the proceeding would have been different.” Id. at 682. To
prove materiality, a defendant need not demonstrate that it is
more likely than not that he would have received a different
  3
    In addressing Horton’s Brady claim, we assume, as the district court
did, that the deal between the police and McLaurin existed as Horton has
alleged. However, as discussed below, because no court has determined
whether the deal existed, we remand to the district court for a resolution
of this potential factual dispute.
5078                   HORTON v. MAYLE
verdict with the evidence; rather, “[a] ‘reasonable probability’
of a different result is . . . shown when the government’s evi-
dentiary suppression ‘undermines confidence in the outcome
of the trial.’ ” Kyles v. Whitley, 514 U.S. 419, 434 (1995)
(quoting Bagley, 473 U.S. at 678).

   We conclude that the state’s failure to disclose McLaurin’s
leniency deal undermines confidence in the outcome of the
trial for two reasons. First, McLaurin’s testimony was central
to the prosecution’s case. See Kyles, 514 U.S. at 444 (finding
that non-disclosed evidence tending to undermine the reliabil-
ity of key witness testimony was material); Giglio v. United
States, 405 U.S. 150, 154-55 (1972) (finding that undisclosed
deal with key prosecution witness was material non-
disclosure); see also Banks v. Dretke, 540 U.S. 668, 699-703
(2004) (finding that non-disclosure of paid-informant status of
key prosecution witness was material). Second, the deal
would have provided powerful and unique impeachment evi-
dence demonstrating that McLaurin had an interest in fabri-
cating his testimony. See Napue v. Illinois, 360 U.S. 264, 270
(1959) (holding that some evidence of bias did not diminish
value of other evidence of bias); Banks, 540 U.S. at 702-03
(finding that impeachment evidence was not “merely cumula-
tive” where the withheld evidence was of a different charac-
ter). We therefore hold that the California Supreme Court’s
summary dismissal of Horton’s Brady claim was an unreason-
able application of clearly established federal law as deter-
mined by the United States Supreme Court in Brady and
related cases.

   [7] McLaurin’s testimony was the glue that held the prose-
cution’s case together. It was McLaurin’s testimony that
described the plot and the motive to attack and kill Bowser.
It was McLaurin’s testimony that linked Horton to the drugs
and money that belonged to Bowser shortly after the murder.
And most importantly, it was McLaurin’s testimony that
revealed that Horton confessed to the crime. As the Supreme
Court has noted, “A confession is like no other evidence.
                       HORTON v. MAYLE                     5079
Indeed, ‘the defendant’s own confession is probably the most
probative and damaging evidence that can be admitted against
him.’ ” Arizona v. Fulminante, 499 U.S. 279, 296 (1991)
(quoting Bruton v. United States, 391 U.S. 123, 139 (1968)
(White, J., dissenting)).

   [8] As the prosecutor emphasized to the jury, McLaurin
provided the only “direct” evidence that connected Horton to
the crime. Indeed, without McLaurin’s testimony, the prose-
cution’s case was entirely circumstantial. No fingerprints,
DNA evidence, or eyewitness testimony placed Horton at the
scene. See Hayes v. Brown, 399 F.3d 972, 985, 988 (9th Cir.
2005) (en banc) (holding that evidence of an undisclosed deal
with a witness was material where the witness’s testimony
regarding the defendant’s confession was undoubtedly the
centerpiece of the prosecution’s case and almost all of the
other evidence against the defendant was circumstantial).

   The Supreme Court observed in Kyles that “[t]he likely
damage [of suppressed evidence] is best understood by taking
the word of the prosecutor . . . .” 514 U.S. at 444. Here, the
prosecutor stated in closing argument that it is “obvious to
everybody in this courtroom that [McLaurin’s] testimony in
this case is very important” and urged three times that the jury
ask to have it read back if they had “some doubt or question
as to what he testified to.” The jury did in fact ask to have
McLaurin’s testimony read back. See Gantt v. Roe, 389 F.3d
908, 915-16 (9th Cir. 2004) (stating that “[w]e also know that
the jury thought carefully about the matchbook because it
submitted a question about it,” in concluding that suppressed
evidence relating to the matchbook was material).

   Further, in discussing the call that Horton allegedly made
to McLaurin after the murder, the prosecutor stated, “If they
didn’t call McLaurin, would this case be solved? I don’t think
anybody would know anything about the case if it weren’t for
the fact that the car broke down and they had to go from
5080                       HORTON v. MAYLE
Ray’s Motel to the Greyhound bus depot.”4 The prosecutor
also argued that despite his drug use, McLaurin was a credi-
ble, valuable witness.

   [9] The prosecutor’s emphasis on the importance of
McLaurin’s testimony bolsters the conclusion that disclosure
of the deal may have significantly damaged the prosecution’s
case. See Hayes, 399 F.3d at 986 (“The importance of James’s
testimony was underscored by the prosecution in its closing
argument.”); Gantt, 389 F.3d at 915 (noting that the prosecu-
tor “spent a good part of his summation arguing the impor-
tance of the matchbook”); cf. Strickler v. Greene, 527 U.S.
263, 295 (1999) (holding that suppressed impeachment evi-
dence was not material where the witness’s testimony “was
not relied upon by the prosecution at all during its closing
argument at the penalty phase”).

   [10] Although certain details of McLaurin’s account were
corroborated by other witnesses, the most damning part of
McLaurin’s testimony—Horton’s confession—was not. Thus,
evidence that would have impeached McLaurin’s credibility
might well have altered the outcome of the trial. See Banks,
540 U.S. at 701 (holding that suppressed evidence of a wit-
ness’s role as an informant was material where his testimony
was the “centerpiece” of the prosecution’s case and noting
that had the evidence been disclosed, the jury “might well
have distrusted [the informant’s] testimony, and, insofar as it
was uncorroborated, disregarded it”); see also Silva v. Wood-
ford, 279 F.3d 825, 854-55 (9th Cir. 2002) (holding that an
evidentiary hearing was warranted on a Brady claim involving
a deal with a witness whose “credibility was a critical issue,
given that he was the only witness who could identify [defen-
dant] as the trigger man”).
   4
     The dissent references pieces of evidence that are consistent with, or
at least not inconsistent with, McLaurin’s testimony; but as the prosecutor
essentially conceded, without McLaurin’s testimony there would have
been no case. This is precisely why his secret deal undermines confidence
in the verdict.
                         HORTON v. MAYLE                        5081
   It is true that McLaurin’s testimony was already severely
impeached by his own admission that he habitually used
drugs, lied to the police, and drove Horton to the bus depot
after the killing. However, that the jury had other reasons to
disbelieve McLaurin does not render the suppressed evidence
of the deal immaterial. Evidence that the prosecution prom-
ised immunity to induce McLaurin to testify as its star witness
is a wholly different kind of impeachment evidence, from
which the jury reasonably could have inferred that McLaurin
had an interest in fabricating his testimony. In Hayes, we held
that disclosure of a deal with the prosecution’s key witness
would not have been “merely cumulative impeachment” evi-
dence, even though the witness was already subject to
impeachment on the basis of transactional immunity, drug
addiction, and his criminal record. 399 F.3d at 987. Rather,
we concluded that the additional disclosure “would have dem-
onstrated that the State was going to great lengths to give [the
witness] a powerful incentive to testify favorably, to the point
of letting him go free on unrelated felony charges.” Id.; see
also Banks, 540 U.S. at 702 (rejecting the government’s argu-
ment that suppressed evidence of a witness’s role as an infor-
mant was immaterial merely because the witness’s testimony
was already impeached on grounds that were not “directly rel-
evant” to his informant status); Napue, 360 U.S. at 270
(“[W]e do not believe that the fact that the jury was apprised
of other grounds for believing that the witness . . . may have
had an interest in testifying against petitioner turned what was
otherwise a tainted trial into a fair one.”).

   [11] Moreover, as this court explained in Benn v. Lambert,
where a witness is central to the prosecution’s case, the defen-
dant’s conviction demonstrates that the impeachment evi-
dence presented at trial likely did not suffice to convince the
jury that the witness lacked credibility. 283 F.3d 1040, 1054
(9th Cir. 2002).5 In such cases, we noted, the suppressed
  5
   Although Supreme Court holdings are the only definitive source of
clearly established federal law for purposes of the AEDPA, we may rely
5082                     HORTON v. MAYLE
impeachment evidence “takes on an even greater importance.”
Id. In Benn, we ultimately held that:

     Where, as here, there is reason to believe that the
     jury relied on a witness’s testimony to reach its ver-
     dict despite the introduction of impeachment evi-
     dence at trial, and there is a reasonable probability
     that the suppressed impeachment evidence, when
     considered together with the disclosed impeachment
     evidence, would have affected the jury’s assessment
     of the witness’s credibility, the suppressed evidence
     is prejudicial.

Id. at 1056. Because McLaurin’s testimony was critical to the
prosecution’s case, we conclude that it is reasonably probable
that the result of the trial would have been different had evi-
dence of the deal been disclosed.

   [12] In sum, we hold that the prosecution’s failure to dis-
close the deal between McLaurin and the police violated
Brady. The rule in this situation is clear and specific: the pros-
ecution must disclose material evidence favorable to the
defense. Brady, 373 U.S. at 87. By implicitly finding that the
suppression of McLaurin’s leniency deal was immaterial, the
state court unreasonably applied Supreme Court-established
federal law set down in Napue, Brady, Giglio, and Kyles. The
recurrent theme of these cases is that where the prosecution
fails to disclose evidence such as the existence of a leniency
deal or promise that would be valuable in impeaching a wit-
ness whose testimony is central to the prosecution’s case, it
violates the due process rights of the accused and undermines
confidence in the outcome of the trial. Napue, 360 U.S. at
270; Giglio, 405 U.S. at 154; Kyles, 514 U.S. at 444. Here, the

on circuit precedent as persuasive authority for determining whether a
state court decision unreasonably applies Supreme Court law. Clark v.
Murphy, 331 F.3d 1062, 1069 (9th Cir.), cert. denied, 540 U.S. 968
(2003).
                           HORTON v. MAYLE                            5083
prosecution failed to disclose a promise of immunity given to
McLaurin, its “star witness,” in exchange for his testimony,
testimony that provided the only evidence of a motive and the
opportunity to kill the victim and that included a confession
by Horton himself. The state court was not only wrong in its
application of these cases, it was objectively unreasonable.
See 28 U.S.C. § 2254(d)(1); Lockyer v. Andrade, 538 U.S. 63,
75-76 (2003); see also Gantt, 389 F.3d at 916 (holding that
the state court’s conclusion that the suppression of evidence
did not violate Brady was an unreasonable application of
clearly established federal law).

   [13] We therefore vacate the district court’s denial of Hor-
ton’s Brady claim and remand to the district court for a deter-
mination whether the state disputes the existence of the deal
between McLaurin and the police. See Gantt, 389 F.3d at 916.
If the state does dispute the deal’s existence, the district court
shall hold an evidentiary hearing to resolve this dispute.6 If
  6
    Although Horton’s habeas petition is governed by the AEDPA, which
limits a district court’s discretion to conduct evidentiary hearings, see 28
U.S.C. § 2254(e)(2) (providing that petitioners who failed to develop the
facts in state court may not obtain an evidentiary hearing in district court
except in limited circumstances), here we assess the availability of an evi-
dentiary hearing under pre-AEDPA law because Horton exercised suffi-
cient diligence in seeking to develop the factual basis of his claim in the
state court proceedings. See Williams v. Taylor, 529 U.S. 420, 437 (2000)
(“If there has been no lack of diligence at the relevant stages of the state
court proceedings, the prisoner has not ‘failed to develop’ the facts under
§ 2254(e)(2)’s opening clause, and he will be excused from showing com-
pliance with the balance of the subsection’s requirements.”).
   Ordinarily diligence requires that a petitioner seek an evidentiary hear-
ing in state court in the manner prescribed by state law. Id. Under Califor-
nia law, an appellate court, when presented with a state habeas petition,
determines whether an evidentiary hearing is warranted only after the par-
ties file formal pleadings, if they are ordered to do so. See People v.
Duvall, 886 P.2d 1252, 1258-61 (Cal. 1995); People v. Romero, 883 P.2d
388, 391-94 (Cal. 1994). Here, the California Supreme Court summarily
denied Horton’s state habeas petition without ordering formal pleadings.
Because Horton never reached the stage of the proceedings at which an
5084                        HORTON v. MAYLE
the state concedes, or if the district court finds after an eviden-
tiary hearing, that the deal existed, the district court shall
grant a writ of habeas corpus ordering that Horton be released
unless the state retries him within a reasonable time to be set
by the district court. See id.

  AFFIRMED IN PART, REVERSED AND REMANDED
IN PART.



RYMER, Circuit Judge, dissenting in part:

   We do not need to know whether or not Donald McLaurin
had a deal that charges would not be pressed against him or
his probation revoked for anything he did on the weekend of
October 10th,1 because even if there were a deal, evidence of
it would not have changed the outcome of Horton’s trial. The
California Supreme Court denied this claim on the merits, but
as it did so without discussion, we independently review the
record to determine whether its decision was objectively rea-
sonable. See Delgado v. Lewis, 223 F.3d 976, 982 (9th Cir.
2000); Pirtle v. Morgan, 313 F.3d 1160, 1167 (9th Cir. 2002)

evidentiary hearing should be requested, he has not shown “a lack of dili-
gence at the relevant stages of the state court proceedings” and therefore
is not subject to AEDPA’s restrictions on evidentiary hearings.
   Under pre-AEDPA law, a habeas petitioner is entitled to an evidentiary
hearing on a claim where the facts are in dispute if (1) he has alleged facts
that, if proven, would entitle him to relief, and (2) he did not receive a full
and fair evidentiary hearing in state court. See Silva, 279 F.3d at 853.
Because, as noted, Horton would be entitled to relief if his allegation of
the deal were proven, and because Horton was not afforded an evidentiary
hearing in state court, Horton is entitled to an evidentiary hearing on his
Brady claim if the state disputes that the deal existed. See id. at 855.
   1
     Horton submitted McLaurin’s declaration to this effect to the Califor-
nia Supreme Court in 1995. There is no other evidence of a deal, and
McLaurin testified at the preliminary hearing that he had no deal.
                        HORTON v. MAYLE                       5085
(noting that although we independently review the record, we
still defer to the state court’s ultimate decision). The district
court assumed (as do I) that an undisclosed deal had been
made, but rejected Horton’s Brady claim because the sup-
pressed evidence was not material. Brady v. Maryland, 373
U.S. 83 (1963). I agree, and would hold that the state court’s
decision was not contrary to, or an unreasonable application
of, clearly established United States Supreme Court law.

   Evidence is material “if there is a reasonable probability
that, had the evidence been disclosed to the defense, the result
of the proceeding would have been different.” Strickler v.
Greene, 527 U.S. 263, 280 (1999) (citing United States v.
Bagley, 473 U.S. 667, 676 (1985), and Kyles v. Whitley, 514
U.S. 419, 433-34 (1995)). “[T]he question is not whether the
defendant would more likely than not have received a differ-
ent verdict with the evidence, but whether in its absence he
received a fair trial, understood as a trial resulting in a verdict
worthy of confidence.” Strickler, 527 U.S. at 289-90 (citing
Kyles, 514 U.S. at 434). Put differently, “the question is
whether ‘the favorable evidence could reasonably be taken to
put the whole case in such a different light as to undermine
confidence in the verdict.’ ” Id. (quoting Kyles, 514 U.S. at
435).

   Evidence of the deal that McLaurin declares he had would
not put the entire case in such a different light that my confi-
dence in the outcome is undermined. Benn v. Lambert, 283
F.3d 1040, 1053 (9th Cir. 2002) (citing Bagley, 473 U.S. at
676; United States v. Agurs, 427 U.S. 97, 111-12 (1976)).
This is so for three reasons: McLaurin was severely
impeached anyway; key parts of his testimony were corrobo-
rated by independent witnesses; and Horton’s own conduct
and statements, apart from those to which McLaurin testified,
were strong evidence of guilt.

  Horton’s connection to the murder was established through
witnesses other than McLaurin who testified that Horton
5086                   HORTON v. MAYLE
asked Graham for a hammer that belonged to Dorn, Graham
gave the hammer to Horton, and neither Graham nor Dorn
saw the hammer again after Graham gave it to Horton. This
was in October; Dorn noticed that the hammer (which he usu-
ally kept in his office) was missing after October 11 but
hadn’t seen it for about a week before that. Horton told Dorn
on the morning of October 10 that “he had something he was
going to do” and that “if it worked out okay” Horton would
be moving out the next day. Dorn saw Horton drive away
with Doonie and Anthony about 9:30 on the morning of the
murder. Bowser was killed by Dorn’s hammer. Horton left
town after the crime was committed. In the next few days
Horton called Dorn a number of times asking if the police
were looking for him (Horton), and Horton told Dorn to tell
Graham that if anyone asked whether Graham had given any-
thing to Horton, to deny it. All of this evidence came in
through witnesses other than McLaurin.

   While McLaurin was an important witness for the prosecu-
tion, he was important primarily because he testified that Hor-
ton said and did things that were consistent with, or
corroborated by, testimony from independent witnesses. For
example: McLaurin testified that he drove Horton to a build-
ing on Artesia Boulevard where Horton went inside, and came
out with drugs; Bowser’s girlfriend Ebel testified that Bowser
sold drugs from his apartment, which is in that building, and
that Horton was a customer whom she had seen in Bowser’s
apartment. McLaurin said that Horton called his dealer a
name with “Lo” in it; Ebel testified that Bowser was known
as “Lobo.” McLaurin testified that Horton and Doonie and he
discussed a plan to rob Horton’s dealer the night before it
happened, and that Horton said he would not use a gun
because it would be too noisy but would use a pipe; a pipe
was not used, but a hammer has similar qualities. McLaurin
testified that Horton said he knew his dealer kept cocaine in
one of the kitchen cabinets; Ebel testified that Bowser kept his
supply in plastic bags inside a container in a cupboard in the
kitchen, that this is where Bowser’s drug deals went down,
                      HORTON v. MAYLE                    5087
and that Horton was a customer. McLaurin testified that Hor-
ton called him about 1:00 p.m. at work and said to meet at
Ray’s Motel; McLaurin’s supervisor testified that McLaurin
left work, having arrived at 5:45 a.m., about 1 p.m. after
receiving a telephone call. McLaurin testified that at Ray’s,
Horton, Doonie and Anthony had two bags of powdered
cocaine and one with cocaine rocks, and that one of the bags
had black “X’s” on it; Ebel testified that Bowser kept two
bags of powdered cocaine and one of rock cocaine in baggies,
one of which was marked with black “X’s.” McLaurin testi-
fied that he also saw a roll of money at Ray’s; Ebel testified
that catering truck money was missing from Bowser’s apart-
ment after the murder. McLaurin testified that Horton said he
clubbed Bowser in the head with a hammer, then went to the
kitchen and got the cocaine; Dorn’s hammer, which Graham
gave to Horton, was within a foot of Bowser’s body, the inju-
ries to Bowser’s head were consistent with hammer blows,
and Ebel as well as a police officer testified that the butter
dish where Bowser kept his cocaine was uncovered and
empty.

   Apart from this, as the district court found, McLaurin had
“credibility problems that were obvious to the jury through
his own contradictory, vague, and sometimes indecipherable
testimony.” McLaurin admitted to: significant drug use while
he was with Horton before and after the crime; being in jail
on probation violations for testing dirty; lying to the police
about taking Horton to the bus depot because he was afraid
he would be arrested for doing it; lying to Horton’s counsel;
and never being charged with a crime in connection with the
events of October 10-11. While evidence of a deal could have
suggested an even stronger motive to lie, the jury knew that
McLaurin participated in planning the crime, would have
driven Horton to Bowser’s on the 10th but for his girlfriend’s
intervention, and drove Horton to the bus station after the
crime — yet was neither arrested nor prosecuted. Making the
inference of bias more specific would not likely have affected
the total mix of information about McLaurin, which included
5088                   HORTON v. MAYLE
the fact that he lied to the police about his involvement in
order to avoid arrest. Nor would it likely have affected the
credibility of testimony that was independently corroborated.
Finally, I cannot see how evidence of a deal would have
affected the weight or credibility of the evidence about Hor-
ton’s statements and conduct to which McLaurin was not per-
cipient and about which he did not testify. Horton’s link to the
murder weapon and his own behavior evincing consciousness
of guilt is not affected at all by testimony adduced through
McLaurin. Cf. Kyles, 514 U.S. at 441-43 (disclosure of very
different contemporaneous eyewitness statements would have
substantially reduced or destroyed their trial testimony).

   Horton contends that the circumstantial evidence in his case
is weaker than in other cases where undisclosed deals were
found material. He points in particular to Singh v. Prunty, 142
F.3d 1157, 1159 (9th Cir. 1998), and Carriger v. Stewart, 132
F.3d 463, 479 (9th Cir. 1997). However, these are not deci-
sions of the United States Supreme Court, which are the deci-
sions by which we are obliged to measure the objective
reasonableness of the California court’s determination.
Regardless, in Singh, the witness concerning whom the prose-
cution failed to disclose a deal provided the only evidence that
the defendant had previously tried to hire him to commit the
murder that the defendant ultimately hired someone else to
commit; here, McLaurin’s testimony was substantially cor-
roborated by independent evidence that connected Horton to
the crime. In Carriger, the prosecution failed to disclose the
only direct witness’s long history of lying to police and blam-
ing his crimes on others, and compounded this failure by
arguing to the jury that the witness was telling the truth about
the defendant’s guilt, whereas in this case the jury heard
ample evidence that McLaurin was a liar.

   Horton also suggests that McLaurin himself could have
been the murderer because he had a window of opportunity
after he left work at 1:00 p.m. and before Ebel returned to
Bowser’s apartment at 2:30 p.m., but no evidence supports
                           HORTON v. MAYLE                           5089
any such theory. Crisp called Ebel, concerned about being
unable to reach Bowser, around noon; McLaurin didn’t leave
work until 1:00 p.m., which his supervisor confirmed that he
did after receiving a telephone call; and there is no evidence
that it would even have been possible for him to get to
Bowser’s, do the deed, ransack the apartment, find the
cocaine, and leave before Ebel arrived. Neither does any evi-
dence connect McLaurin with the hammer, or manifest any
consciousness of guilt except with respect to driving Horton
to the bus depot.

   Finally, Horton supposes that someone other than he —
Cunnigan, for instance — could have provided the description
of the crime to McLaurin, or that McLaurin could have
learned specifics from reading the police report, which he
admittedly did before testifying. That Cunnigan could have
told him anything more than what McLaurin acknowledged is
pure speculation; and, as the district court noted, McLaurin
said that he read the police report before testifying at trial, but
his testimony at the preliminary hearing was consistent with
his trial testimony and there is no evidence that he read the
police report before testifying at that hearing.

   Accordingly, I agree with the district court that the Califor-
nia Supreme Court’s rejection of Horton’s Brady claim on the
merits was not contrary to, or an unreasonable application of,
Supreme Court law.2
  2
    Horton argues that the Brady error was compounded by the trial court’s
instruction that the jury must not consider why other persons than the
defendant who were or may have been involved in the crime were not
being prosecuted in this trial or whether they have been or will be prose-
cuted. Whether the instruction was erroneously given is not a certified
issue on appeal. In any event, this admonition was part of an instruction
that stated “[t]here has been evidence in this case indicating that persons
other than defendant were or may have been involved in the crime for
which the defendant is on trial.” The instruction does not preclude jurors
from considering involvement to the extent it bears on credibility or any
thing else; it simply precludes considering why those persons are not
defendants “in this trial.” Horton also relies upon juror declarations to
show prejudice but, as the district court held, they are inadmissible to
impeach the verdict. Fed. R. Evid. 606(b).
