                  FOR PUBLICATION
  UNITED STATES COURT OF APPEALS
       FOR THE NINTH CIRCUIT

MARK HENRY LANKFORD,                       No. 99-99015
               Petitioner-Appellant,
                                              D.C. No.
                 v.
                                          CV-92-00321-S-
ARVON J. ARAVE, Warden, Idaho                   WFN
State Correctional Institution,
                                             OPINION
              Respondent-Appellee.
                                       
     Appeal from the United States District Court
               for the District of Idaho
 Wm. Fremming Nielsen, Senior District Judge, Presiding

                Argued November 15, 2005
                Submitted October 30, 2006
                   Seattle, Washington

                  Filed November 7, 2006

    Before: Stephen Reinhardt, William A. Fletcher, and
               Jay S. Bybee, Circuit Judges.

                  Opinion by Judge Bybee




                            18291
18294                 LANKFORD v. ARAVE


                          COUNSEL

Andrew Parnes, Ketchum, Idaho, for the appellant.

LaMont Anderson, Deputy Attorney General, Boise, Idaho,
for the appellee.


                          OPINION

BYBEE, Circuit Judge:

   In this pre-AEDPA case, we are called upon to review
counsel’s performance in a twenty-two year old capital mur-
der trial. Finding that the record is clear that counsel
requested critical jury instructions that were correct under fed-
eral law but clearly in error under Idaho law and that the error
was not harmless, we reverse the judgment of the district
court and grant the writ.

             I.   FACTS AND PROCEEDINGS

   Robert and Cheryl Bravence were reported missing when
they failed to arrive at a relative’s house following an
                        LANKFORD v. ARAVE                       18295
extended camping trip in the summer of 1983. One week
later, officials discovered their van abandoned at a Los Ange-
les bus terminal. In September, hunters found the couple’s
remains in a remote Idaho campground, not far from their last
known campsite. The skulls of both were badly damaged,
indicating they had died of blunt trauma to the head.

   Two brothers, Mark and Bryan Lankford, were arrested for
the murders. Investigators found Mark’s car about a quarter
of a mile from the victims’ bodies and his handwriting on
credit slips for food and lodging purchased with the victims’
stolen credit cards. Investigators found both brothers’ finger-
prints in the Bravences’ abandoned van, and they found Mr.
Bravence’s knife—with Bryan’s initials newly carved into the
scabbard—in Bryan’s possession.

   The brothers were convicted, in separate trials, and sen-
tenced to death on the same day. Bryan’s sentence was over-
turned on appeal based on the sentencing agreement he
received in return for his testimony against Mark.1 Although
there was strong circumstantial evidence connecting the
Lankfords to the murders, there were no witnesses to the
crime, and no murder weapon was discovered. Bryan’s testi-
mony was critical to establishing the government’s theory that
Mark actually killed the Bravences. At Mark’s trial, the state
relied heavily on Bryan’s uncorroborated eyewitness testi-
mony that Mark committed the murders, beating the Bra-
vences to death with a small club or nightstick. When
interviewed by police, Bryan claimed that both brothers went
to the campsite. While Bryan engaged the campers in conver-
sation,

      Mark came running in to the camp and told the man
      to get down on the ground so he did and Mark pulled
      out a stick like a night stick that a policeman wears
  1
   Under cross examination, Bryan admitted at trial that he expected to
receive an indeterminate life sentence in return for his testimony.
18296                 LANKFORD v. ARAVE
    but only about a foot long and hit the man on the
    back of the neck [k]nocking him out he hit the man
    at least twice and the lady came up a few seconds
    latter [sic] and Mark told here [sic] to get down on
    the ground also and she did and then he hit her once
    I think . . . .

At Mark’s trial, Bryan claimed Mark hit Robert Bravence
“twice. It could have been once.” At his own trial, Bryan
described one blow and added, “I think he struck the man
another time.” He said the blows were aimed “both times in
the back of the neck actually. Not in the head. Kind of across,
you know, across the neck in the back.” He testified that Mark
then struck Cheryl, also “across the back of the neck,” “one
time as I can remember,” “only once . . . . [I]t could have been
more. I don’t know.” Although Bryan admitted that his emo-
tions might have interfered with his perception, in both his
trial and in Mark’s trial he maintained that Mark hit the cou-
ple in the back of the neck, striking Robert twice and Cheryl
once. Throughout the two trials, and in statements to investi-
gators, Bryan described the murder weapon variously as pos-
sibly a “pipe,” “sort of a nightstick” made of wood, “a little
limb deal,” and a “little club” only twelve inches long. Inves-
tigators found a nightstick in Mark’s abandoned car, but could
not tie it to the murders and did not introduce it into evidence.

   Mark did not testify at either trial, but he maintained (in
statements to his attorney and to the police) that Bryan had
confessed to committing the murders and enlisted his help to
hide the bodies. Mark claimed that Bryan went to the couple’s
camp while the brothers were separated and attacked the
campers, crushing their skulls with a large rock. Mark said the
brothers had traveled from Texas to Idaho because Mark was
trying to get away from what he perceived to be his “material-
istic” life in Texas, while Bryan wanted to escape an impend-
ing arrest for parole violations. They camped in Idaho at a
remote site near Grangeville. After Bryan decided he wanted
to return to Texas, Mark left Bryan to hitchhike his way into
                      LANKFORD v. ARAVE                  18297
town. He gave Bryan fifty dollars, told him not to do anything
“stupid,” and started walking back to the campsite. Before he
reached the site some miles away, Bryan drove up in the
stolen van. He initially refused to tell Mark how he stole the
van, exclaiming “I got it. That’s what counts” and complain-
ing “what are all these questions, I told you, don’t worry
about it!” Finally after several questions, Bryan told Mark
about his attack on the Bravences, claiming he hit Robert “in
the head with my shotgun stock. I didn’t hit him too hard, just
to knock him out. I pinched his leg and he didn’t move so I
thought he was out of it.” When Cheryl appeared, he struck
her, too “but not as hard. She was out like a light.” Mark
insisted the two return to the Bravences’ camp, telling Bryan
“[I]t’s not too late to save your ass, maybe.” As the two
neared the site, Bryan grew increasingly nervous. According
to Mark, “[Bryan’s] driving was getting reckless and he was
chain-smoking the entire time.” “The closer we got to the
place, the more nervous [Bryan] became.” At the site, Mark
immediately spotted the two figures, each lying with its head
in a pool of blood. He checked for pulses and told Bryan
“they’re both dead.” Bryan replied “Are you sure?” “They
can’t be!” Mark then confronted Bryan: “shotgun butt? Tell
me the truth.” “It was just like I said,” Bryan explained,

    But after I hit the woman, the man started trying to
    get up, so I hit him again. He went down, but was
    still moving a little. I hit him again, but he wouldn’t
    knock out. So I saw this rock, I picked it up and
    dropped it on his head twice. He stopped moving. I
    picked it (rock) up again and hit the woman.

   After Bryan and his brother were convicted in 1984, Bryan
recanted his testimony against Mark on multiple occasions.
He also recanted his recantations. In a conversation with a
newspaper reporter, in a written statement after his own sen-
tencing, and again at a hearing on Mark’s second motion to
reopen, Bryan admitted responsibility for the murders, claim-
ing he killed the Bravences with a rock. Bryan contacted a
18298                 LANKFORD v. ARAVE
local reporter in June of 1984, after the brothers had been con-
victed, but before either was sentenced. In October of 1984,
at a hearing on Mark’s first motion for a new trial, the
reporter testified that Bryan telephoned him to confess, saying
he “[w]anted the truth to come out,” and admitting that he
killed the Bravences by knocking Mr. Bravence unconscious
with a stick and then beating them both with a rock. In this
version of Bryan’s story, Mark was not on the scene. Bryan
also testified at Mark’s hearing, admitting to the confession
but claiming it was a lie that Mark directed him to make so
“he would get out, therefore, they would have to let me out.”

   Later, in 1985, Bryan wrote a letter to Mark’s counsel again
accepting full responsibility. This prompted a subsequent
hearing on Mark’s second motion for a new trial. This time
Bryan testified that he entered the Bravences’ camp alone,
carrying a 12-gauge shotgun, and ordered the couple to lie
down. He crushed their skulls with “a rock, a large boulder”
that was “about a foot in diameter [and] probably weighed
about thirty-five or forty pounds or more.” He struck each
camper three or four times, and then walked back to the road
to enlist Mark’s help in hiding the bodies. Bryan described the
Bravences’ campground and his attack on the campers in
detail, and admitted that his earlier testimony against Mark
was an attempt to “save [him]self.” The court denied Mark’s
motions for a new trial. In 1998, while he was awaiting re-
sentencing, Bryan again contacted Mark’s counsel, asking to
speak with him. Bryan’s lawyer objected to the proposed
interview, threatening to withdraw if Bryan insisted upon
meeting with Mark’s attorney. As late as April 2003 in a letter
to Mark’s appellate counsel, Bryan continued to assume full
responsibility, confessing that he struck both the Bravences
“several times” with “a head size rock.”

   Mark pursued his state appeals, post-conviction relief, and
state habeas relief, then (after several false starts) he filed a
federal habeas petition. His ineffective assistance claims were
initially dismissed because they had not been properly pre-
                      LANKFORD v. ARAVE                  18299
sented to the Idaho courts. However, the parties stipulated to
an evidentiary hearing on Sixth Amendment claims after we
ruled in Hoffman v. Arave, 236 F.3d 523 (9th Cir. 2001), that
Idaho procedural rules for state habeas claims “frustrate[d]
[prisoners’] exercise of a federal right” and were “inadequate
to preclude federal [review].” Id. at 531 (internal quotation
marks omitted).

   Among the grounds raised in his state and federal habeas
proceedings, Mark contended that ineffective assistance from
his trial counsel, Gregory FitzMaurice, deprived him of his
Sixth Amendment right to counsel. Mark argued that Fitz-
Maurice failed to consult with an independent forensic pathol-
ogist, which would have shown the weaknesses in the state’s
theory that Mark committed the murders; that FitzMaurice
failed to impeach Bryan’s testimony concerning the murder
weapon; and that FitzMaurice requested an erroneous jury
instruction that reduced the state’s burden to provide corrobo-
rating evidence. The district court concluded that as to the
forensic evidence, FitzMaurice made a “reasonable strategic
decision” to present an alibi defense. The district court also
concluded that FitzMaurice did impeach Bryan. Finally, with
respect to the jury instruction, the district court found that
FitzMaurice’s requested jury instruction was erroneous and
that his performance in this regard was deficient. The court
concluded, however, that Mark did not suffer prejudice as a
result.

   FitzMaurice requested and received the following instruc-
tion on accomplice testimony, cited in the record as instruc-
tion number 15:

    An accomplice is one who unites with another per-
    son in the commission of a crime, voluntarily and
    with common intent. An accomplice does not
    become incompetent as a witness because of partici-
    pation in the crime charged. On the contrary, the tes-
    timony of one who asserts by his testimony that he
18300                 LANKFORD v. ARAVE
    is an accomplice, may be received in evidence and
    considered by the jury, even though not corrobo-
    rated by other evidence, and given such weight as
    the jury feels it should have. The jury, however,
    should keep in mind that such testimony is always to
    be received with caution and considered with great
    care.

      You should never convict a defendant upon the
    unsupported testimony of an alleged accomplice,
    unless you believe that unsupported testimony
    beyond a reasonable doubt.

(emphasis added).

   FitzMaurice also submitted two additional instructions
which contradicted instruction 15 by requiring that the jury
find corroboration before accepting any accomplice testi-
mony. Instruction 18 read:

    You are instructed that a defendant cannot be found
    guilty based upon the testimony of an accomplice
    unless such testimony is corroborated by other evi-
    dence which tends to connect such defendant with
    the commission of the offense.

Instruction 19 provided:

    To corroborate the testimony of an accomplice there
    must be evidence of some act or fact related to the
    offense which, if believed, by itself and without any
    aid, interpretation or direction from the testimony of
    the accomplice, tends to connect the defendant with
    the commission of the offense charged.

      However, it is not necessary that the evidence of
    corroboration be sufficient in itself to establish every
                      LANKFORD v. ARAVE                   18301
    element of the offense charged, or that it corroborate
    every fact to which the accomplice testifies.

       In determining whether an accomplice has been
    corroborated, you must first assume the testimony of
    the accomplice has been removed from the case.
    You must then determine whether there is any
    remaining evidence which tends to connect the
    defendant with the commission of the offense.

       If there is not such independent evidence which
    tends to connect defendant with the commission of
    the offense, the testimony of the accomplice is not
    corroborated.

      If there is such independent evidence which you
    believe, then the testimony of the accomplice is cor-
    roborated.

   Mark claims that the instructions were not only inconsis-
tent, but that instruction 15 is an incorrect statement of Idaho
law. After three days of testimony, the district court held that
the instruction was in error and found that FitzMaurice was
ineffective in offering the erroneous instruction. The court
also found FitzMaurice deficient in failing to research and
present mitigating evidence at Mark’s sentencing. However,
the court ultimately denied the petition, finding there was no
prejudice.

               II.   STANDARD OF REVIEW

   Lankford’s petition predates the Antiterrorism and Effec-
tive Death Penalty Act (AEDPA) and is therefore not gov-
erned by it. We review the district court’s denial of the
petition de novo. Turner v. Calderon, 281 F.3d 851, 864 (9th
Cir. 2002). Because ineffective assistance of counsel is a
mixed question of law and fact, we review this claim de novo.
18302                      LANKFORD v. ARAVE
See Silva v. Woodford, 279 F.3d 825, 835 (9th Cir. 2002). We
review factual determinations for clear error. Id.

                           III.   ANALYSIS

   [1] Under Strickland v. Washington, 466 U.S. 668, 687
(1984), Lankford may only prevail in his claim of ineffective
assistance of counsel if he can show deficient representation
“so serious that counsel was not functioning as the ‘counsel’
guaranteed the defendant by the Sixth Amendment.” He must
also show “that counsel’s errors were so serious as to deprive
the defendant of a fair trial, a trial whose result is reliable.”
Id. These two elements of Strickland are generally referred to
as the “performance” and “prejudice” prongs. We evaluate
each in turn.

                                     A

   [2] As we review FitzMaurice’s performance, we must
refrain from second-guessing his strategies and acknowledge
the “wide range of reasonable professional assistance.” Id. at
689. Nevertheless, we must hold FitzMaurice to his “duty to
bring to bear such skill and knowledge as will render the trial
a reliable adversarial testing process.” Id. at 688. Even consid-
ering “conduct from counsel’s perspective at the time,” in at
least one respect, FitzMaurice’s representation falls below the
standard of “reasonable professional assistance.” Id. at 689.
We agree with the district court that there was no reasonable
tactical advantage in requiring an erroneous jury instruction
that would allow the jury to give greater weight to Bryan’s testi-
mony.2 In this case, “[c]ounsel’s errors with the jury instruc-
  2
   In the evidentiary hearing in district court, the state attempted to char-
acterize FitzMaurice’s selection of the instruction as a tactical move, argu-
ing that there was sufficient corroboration and that the jury would not be
able to find Bryan credible beyond a reasonable doubt without corroborat-
ing evidence. FitzMaurice could not confirm the theory, explaining “I
can’t tell you at this point in time . . . my motivations of asking [for] that
                           LANKFORD v. ARAVE                         18303
tions were not a strategic decision to forego one defense in
favor of another. They were the result of a misunderstanding
of the law.” United States v. Span, 75 F.3d 1383, 1390 (9th
Cir. 1996).

   [3] The error in the instructions requested by FitzMaurice
is obvious. Instruction 15 left out a critical element of Idaho
law controlling the use of accomplice testimony: the require-
ment of corroboration. Idaho law provides:

     A conviction cannot be had on the testimony of an
     accomplice, unless he is corroborated by other evi-
     dence, which in itself, and without the aid of the tes-
     timony of the accomplice, tends to connect the
     defendant with the commission of the offense; and
     the corroboration is not sufficient, if it merely shows
     the commission of the offense, or the circumstances
     thereof.

IDAHO CODE § 19-2117 (2005) (emphasis added). As the Idaho
Supreme Court has explained, “ ‘[the] statute . . . absolutely
prohibits a conviction in a criminal case upon the uncorrobo-
rated testimony of an accomplice, even although [sic] the jury
may believe such testimony to be entirely true, and that it
establishes the defendant’s guilt beyond a reasonable
doubt.’ ” State v. Emmons, 495 P.2d 11, 15 (Idaho 1972)
(quoting State v. Carr, 42 P. 215, 216 (Or. 1895) (evaluating
a statute that the Emmons court deemed “essentially the same
as I.C. § 19-2117”)).

  [4] The Idaho statute reflects the state’s unwillingness to
hand down convictions based solely on accomplice testimony.
As the court in Emmons observed:

jury instruction. That appears to be a plausible reason, but I can’t tell you
honestly that was my reason at the time.” Even if FitzMaurice did intro-
duce the instruction in order to draw attention to Bryan’s credibility, a
general instruction on reasonable doubt could have served the same pur-
pose without eliminating the corroboration requirement.
18304                 LANKFORD v. ARAVE
    [T]he criminal law has shown the sources of such
    testimony to be generally so corrupt as to render it
    unworthy of belief, and that it is therefore better as
    a matter of public policy to forbid a conviction on
    the uncorroborated testimony of an accomplice,
    although the guilty may thereby sometimes escape
    punishment, than to leave it possible for the convic-
    tion of an innocent person on such testimony.

Id. (quoting Carr, 42 P. at 216); see id. (“We concur with the
reasoning of the Oregon Supreme Court . . . .” ). The Idaho
Court of Appeals has explained that “[t]his statutory corrobo-
ration requirement is intended to protect against the danger
that an accomplice may wholly fabricate testimony, incrimi-
nating an innocent defendant in order to win more favorable
treatment for the accomplice.” Matthews v. State, 28 P.3d
387, 390 (Idaho Ct. App. 2001).

   [5] FitzMaurice explained that he performed his research at
the library of the University of Idaho Law School, that there
were no model instructions for Idaho at the time, and it seems
that he took the instruction from a collection of federal
instructions. In this, FitzMaurice was dutiful, conscientious—
and quite in error. Federal law permits bare accomplice testi-
mony, while Idaho expressly forbids it. Compare Emmons,
495 P.2d at 15, and State v. Gillum, 228 P. 334, 334 (Idaho
1924), with Darden v. United States, 405 F.2d 1054, 1056
(9th Cir. 1969) (noting that “a conviction in federal court may
be based on the uncorroborated testimony of an accomplice”).
FitzMaurice simply overlooked important differences
between Idaho law and federal law. It was a young lawyer’s
mistake, akin to failing to check the pocket part, but it was a
mistake, plainly enough. As the district court noted, “[s]imply
reviewing the three instructions would have revealed that two
instructions . . . conformed with Idaho’s law regarding accom-
plice testimony, while [the third] was substantially different,
as well as not being in conformance with Idaho law.”
                           LANKFORD v. ARAVE                         18305
   [6] FitzMaurice’s error is perhaps understandable, given his
limited experience and resources,3 but it is constitutionally
inexcusable. By inviting a jury instruction that misstated state
law and made it easier for the jury to convict his client, coun-
sel unwittingly undermined the very “adversarial testing pro-
cess” he was supposed to protect. Strickland, 466 U.S. at 688.
We agree with the district court that in this regard his perfor-
mance fell below the “range of reasonable professional assis-
tance.” Id. at 689.

                                     B

   [7] Whether the erroneous instruction rendered the ultimate
verdict in this case unreliable is a harder question. “It is not
enough for the defendant to show that the errors had some
conceivable effect on the outcome of the proceeding.” Id. at
693. To reverse we must find a “reasonable probability that
. . . the result of the proceeding would have been different”
had the erroneous instruction not been given. Id. at 694; see
also Span, 75 F.3d at 1390. And we must consider the instruc-
tions “as a whole” in evaluating the magnitude of the error.
Middleton v. McNeil, 541 U.S. 433, 437 (2004). “[A] single
instruction to a jury may not be judged in artificial isolation,
but must be viewed in the context of the overall charge.”
Boyde v. California, 494 U.S. 370, 378 (1990) (internal quota-
tion marks omitted); see also Estelle v. McGuire, 502 U.S. 62,
72 (1991). Accordingly, Mark need not establish error for cer-
tain. “[A] defendant need not establish that the jury was more
likely than not to have been impermissibly [influenced] by the
instruction.” Boyde, 494 U.S. at 380. “If the charge as a whole
is ambiguous, the question is whether there is a reasonable
  3
    FitzMaurice was a part-time public defender who had, it seems, only
tried one previous major felony: a case of cattle-rustling. He had never
defended a murder case, and had no training in capital defense. He deliv-
ered no opening statement to the jury, and called no witnesses. He did not
secure a second attorney, an investigator (except for a fingerprint analyst),
an independent pathologist, or an independent psychologist to aid in pre-
paring a defense.
18306                 LANKFORD v. ARAVE
likelihood that the jury has applied the challenged instruction
in [an impermissible] way . . . .” Middleton, 541 U.S. at 437
(internal quotation marks omitted) (emphasis added).

   The government argues that any error was cured because
there were additional, proper instructions (instructions 18 and
19) that arguably contradicted instruction 15. Instruction 18
stated that “a defendant cannot be found guilty based upon the
testimony of an accomplice unless such testimony is corrobo-
rated by other evidence which tends to connect such defen-
dant with the commission of the offense.” (emphasis added).
Instruction 19 defined “corroboration” and instructed the jury
to “assume the testimony of the accomplice has been removed
from the case. You must then determine whether there is any
remaining evidence which tends to connect the defendant with
the commission of the offense.”

   When instructions 15 and 18 are read together they can be
reconciled, but not in a way that is helpful to the state.
Instruction 18 plainly states that “a defendant cannot be found
guilty based upon the testimony of an accomplice unless such
testimony is corroborated by other evidence.” That, of course,
contradicts instruction 15 which states that an accomplice’s
testimony “may be received in evidence and considered by
the jury, even though not corroborated by other evidence.”
The two statements seem to be bridged by the last sentence
of instruction 15: “You should never convict a defendant
upon the unsupported testimony of an alleged accomplice,
unless you believe that unsupported testimony beyond a rea-
sonable doubt.” This line appears to create an exception to
instruction 18’s warning not to credit uncorroborated testi-
mony: The testimony can be credited if the jury believes it
beyond a reasonable doubt. To the trained legal eye, the “be-
yond a reasonable doubt” adds nothing to instruction 15
because a criminal jury generally must find proof beyond a
reasonable doubt to return a guilty verdict. See Cool v. United
States, 409 U.S. 100, 104 (1972); In re Winship, 397 U.S.
358, 362 (1970). Nevertheless, a conscientious jury might
                           LANKFORD v. ARAVE                           18307
read instructions 15 and 18 together to state a general rule and
its exception: A defendant cannot be found guilty based upon
the testimony of an accomplice unless either (a) such testi-
mony is corroborated by other evidence, or (b) the jury
believes the unsupported testimony beyond a reasonable
doubt. The instructions, thus reconciled, remain contrary to
Idaho law. Accordingly, the jury could have convicted Lank-
ford either because they found Bryan’s testimony to be ade-
quately supported,4 or because they believed his
uncorroborated testimony beyond a reasonable doubt.
“[W]hen a case is submitted to the jury on alternative theories
the [impermissible legal error in] any of the theories requires
that the conviction be set aside.” Leary v. United States, 395
U.S. 6, 31-32 (1969); see also United States v. Griffin, 502
U.S. 46, 59 (1991) (“[T]he term ‘legal error’ means a mistake
about the law, as opposed to a mistake concerning the weight
or the factual import of the evidence.”).

   [8] It is hard to imagine a case in which such an instruc-
tional error could have caused more damage. Erroneous
instruction 15 went to the heart of the case. Although there is
overwhelming evidence that one or both of the Lankford
brothers killed the Bravences, only Bryan’s testimony singled
out Mark as the killer. There were no witnesses to the murder,
and no murder weapon was admitted into evidence. There was
no forensic or circumstantial evidence suggesting that Mark,
rather than Bryan, beat the victims to death. Bryan’s testi-
mony was vital to the prosecution, and instruction 15 allowed
the jury to convict Mark on Bryan’s word alone, in obvious
violation of Idaho law. Moreover, Bryan had every incentive
to lie: If Mark did not kill the Bravences, then Bryan must
  4
    There is another possibility, also not helpful to the state. The jury could
have read instruction 15 to mean that they could convict Mark on Bryan’s
unsupported testimony if they believed Bryan beyond a reasonable doubt.
Or, they could convict Mark even if they did not believe Bryan beyond
a reasonable doubt so long as there was some evidence to corroborate his
testimony. This latter possibility would, of course, flatly violate In re Win-
ship.
18308                LANKFORD v. ARAVE
have done the deed. Additionally, Bryan thought he had a deal
to avoid the death penalty in exchange for his testimony
against his brother. See Lankford v. Idaho, 500 U.S. 110, 120-
121 (1991); State v. Lankford, 903 P.2d 1305, 1309 (Idaho
1995). This is precisely the declared purpose for Idaho’s cor-
roboration requirement: “to offset the danger that an accom-
plice may wholly fabricate testimony, inculpating an innocent
person, in order to purchase immunity from prosecution, or
lenient treatment, for his own complicity in the crime.” State
v. Pierce, 685 P.2d 837, 842 (Idaho Ct. App. 1984) (citations
omitted).

   [9] Considering the instruction “in the context of the
instructions as a whole and the trial record” does not inspire
confidence in the reliability of Mark’s verdict. Estelle, 502
U.S. at 72. The state nonetheless attempts to salvage Mark’s
conviction by relying on Idaho law, which provides that “[a]n
error in failing to give [a corroboration] instruction may be
harmless if ample corroborative evidence was presented.”
State v. Hill, 97 P.3d 1014, 1019 (Idaho Ct. App. 2004). The
state contends that the prosecution presented corroboration
adequate to meet the requirements of Idaho Code § 19-2117.

  The Idaho Supreme Court has explained in general terms
what corroborating evidence is required by § 19-2117:

    The statute permits convictions upon the testimony
    of an accomplice with the limitation that the accom-
    plice shall be corroborated by such other evidence as
    tends to connect the defendant with the commission
    of the crime, and hence the corroborative evidence
    must be independent of the testimony of the accom-
    plice and connect or tend to connect the defendant
    with the commission of the crime charged. Corrobo-
    ration of an accomplice need only connect the
    accused with the crime, it may be slight, and need
    only go to one material fact. It may be entirely cir-
    cumstantial. The jurors are the judges of the weight
                      LANKFORD v. ARAVE                   18309
    and credibility of the testimony under proper instruc-
    tions.

State v. Garcia, 630 P.2d 665, 672 (Idaho 1981) (quoting
State v. Bassett, 385 P.2d 246, 248 (Idaho 1963)) (citations
omitted). Idaho courts have also explained that:

    No general rule can be stated with respect to the
    quantum of evidence corroborating an accomplice’s
    testimony which is necessary to warrant a convic-
    tion; each case must be governed by its own circum-
    stances, keeping in view the nature of the crime, the
    character of the accomplice’s testimony, and the
    general requirements with respect to corroboration.

Gillum, 228 P. at 336. We note that most of the Idaho cases
addressing the statute arose as claims disputing the suffi-
ciency of the evidence, not in the context of an erroneous
instruction, and in sufficiency cases “[the c]ourt will construe
all of the evidence in favor of upholding the verdict.” Hill, 97
P.3d at 1018. In such cases, the court must uphold the jurors’
verdict if there is any basis for a finding of corroboration
because they are “the judges of the weight and credibility of
the testimony under proper instructions.” Garcia, 630 P.2d at
672 (emphasis added) (quoting Bassett, 385 P.2d at 248); see
also State v. Gonzales, 438 P.2d 897, 901 (Idaho 1968).

   [10] The error here is a more fundamental one. The jury
was instructed to overlook the question of corroboration, and
we must ask whether, given proper instructions, there is a
“reasonable probability” that the jury would have found
Bryan’s testimony unsupported. “A reasonable probability is
a probability sufficient to undermine confidence in the out-
come.” Strickland, 466 U.S. at 694. The Idaho cases suggest
that, where the trial court has refused a corroboration instruc-
tion under § 19-2117, the Idaho Supreme Court has demanded
substantial evidence of corroboration before it will find the
error harmless. In State v. Scroggins, 716 P.2d 1152 (Idaho
18310                 LANKFORD v. ARAVE
1985), the Idaho Supreme Court found that the trial court
committed harmless error when it omitted the corroboration
instruction in a felony murder conviction where Scroggins
“admitted that he assisted [the accomplice] in taking the vic-
tim to the creek, that he, Scroggins, had handcuffed the vic-
tim, that [the accomplice] had used Scroggins’ knife, that he,
Scroggins, had attempted to rape the victim and that he had
been in the vicinity when [the accomplice] had, in fact, raped
and murdered the victim.” Id. at 1158. The Court concluded
that “although Scroggins’ testimony did not corroborate [the
accomplice’s] version of the facts, it was sufficient to permit
a finding that Scroggins was connected with the commission
of the offense.” Id. In Matthews v. State, 28 P.3d 387 (Idaho
Ct. App. 2001), Matthews sought post-conviction relief from
his conviction for first degree murder. Id. at 389-90. Mat-
thews argued that his counsel was ineffective because he
failed to request a jury instruction on corroboration of accom-
plice testimony. The court concluded that the jury should have
been instructed, but it found the error was harmless. Matthews
had admitted that he joined four other juveniles in beating the
victim; testimony from other witnesses also corroborated the
testimony from Matthews’s accomplices. In this case, “the
outcome of the trial would [not] have been different had Mat-
thews’s counsel requested a jury instruction regarding the cor-
roboration of accomplice testimony. Id. at 391-92.

   These cases, in which there was substantial corroborating
evidence, contrast with the Idaho Supreme Court’s decision in
State v. Gonzales, 438 P.2d 897 (Idaho 1968). In that case, the
Idaho Supreme Court held that failure to give the corroborat-
ing evidence instruction was not harmless even though the
evidence included witnesses who saw the defendant fight with
the victim before the murder and who recognized the defen-
dant’s car at the subsequent drive-by shooting. Id. at 899, 901.
Investigators found a spent cartridge at the defendant’s house
and a rifle at his mother’s apartment. Id. at 900. The defen-
dant allegedly asked police at his booking, “How is the fellow
I shot, is he ded [sic] or what?” Id. at 899. Even with all of
                      LANKFORD v. ARAVE                   18311
this evidence, the Court reversed the conviction because the
testimony of an accomplice (a passenger in the car) was not
properly limited with a corroboration instruction. “[T]he
[trial] court had a duty to instruct the jury on all matters of
law necessary for their information,” the Court explained,
“and the defendant was entitled to have his theory of the case
submitted to the jury upon proper instructions.” Id. at 901.

   The nature of the evidence sufficient to corroborate is fur-
ther explained in State v. Campbell, 757 P.2d 230 (Idaho Ct.
App. 1988). In that case, Campbell was accused of kidnaping
and murder. Id. at 231. He argued that there was insufficient
evidence to corroborate the testimony of his two accomplices,
who testified that Campbell had repeatedly kicked the victim.
The state introduced a pathologist who testified that the vic-
tims injuries were consistent with the testimony of the accom-
plices. The Idaho Court of Appeals held that this was not
sufficient:

    Without any question, the autopsy corroborated the
    accomplices’ testimony describing the infliction of
    severe injuries on Atwood. However, under I.C.
    § 19-2117, evidence that is merely corroborative of
    the “commission of the offense, or the circumstances
    thereof” is not enough. Instead, the evidence neces-
    sary to serve as corroboration of the accomplice’s
    testimony must tend “to connect the defendant with
    the commission of the offense.”

Id. at 232-33. Although the pathologist’s report was not suffi-
cient corroboration, the court found sufficient corroboration in
other evidence, including statements that Campbell made to
others. Id. at 233-34.

   [11] The corroborative evidence the state points to in this
case—including, principally, the testimony of the state’s
pathologist, Dr. Robert Cihak—implicates the Lankfords gen-
erally, not Mark specifically. There is no evidence that
18312                 LANKFORD v. ARAVE
uniquely points to Mark as the perpetrator. All of the state’s
evidence equally implicates Bryan. The only physical evi-
dence presented at trial was circumstantial, and all of that evi-
dence also linked Bryan to the murders. The only evidence
tending to show that Mark was the killer was his brother’s
word. We conclude there is a “reasonable probability” that,
with proper instructions on the question of corroboration, the
jury would not have convicted Mark of first degree murder.
Strickland, 466 U.S. at 694.

   [12] We find FitzMaurice’s error in drafting jury instruc-
tions an adequate grounds for reversal. Although we do not
reach the other grounds on which Mark contends that Fitz-
Maurice rendered ineffective assistance of counsel, the evi-
dence Mark has presented in support of those claims
reinforces our judgment that Mark was prejudiced in this case.
At the federal evidentiary hearing, Mark presented experts
who questioned the reasonableness of FitzMaurice’s failure to
hire an independent forensics expert to investigate Mark’s
claim that Bryan beat the Bravences with a large river rock.
The testimony of Dr. Todd Grey, forensic pathologist and
chief medical examiner for the state of Utah, strongly sug-
gests that an independent forensic investigation would have
revealed serious flaws in Bryan’s story that Mark beat the
Bravences with a stick. He pointed out that the “extensive
fragmentation” of the victim’s skulls suggests the couple were
bludgeoned with a larger object, such as the river rock Mark
described. He described Cheryl Bravence’s skull as “a pile of
bones” before it was reconstructed by forensics experts, and
explained that her skull showed multiple linear and branching
fractures. In at least one area, parts of the bone were missing
where bone had been broken off and driven downwards into
her brain. Robert Bravence’s skull also required reconstruc-
tion, and it had to be reinforced with clay where sections of
bone were missing. Because the Bravences’ skulls showed
“extensive fracturing,” “depression of bone,” and “fragmenta-
tion” on virtually all sides, Dr. Grey concluded that their inju-
ries were “much more consistent with the scenario in which
                       LANKFORD v. ARAVE                   18313
these individuals were struck with the large rock.” To cause
this level of destruction with a twelve-inch stick, the expert
testified, “would take a tremendous amount of force,” “an
horrendous amount of force.” “I am not saying it is impossi-
ble,” Dr. Grey explained, “but it would certainly take a lot of
effort.” Although Bryan claimed Mark dealt Robert a “hard
blow” that necessarily dislodged portions of his skull, Bryan
testified at his own trial that there were no sounds “such as
bones breaking” and that there was no blood. The single
skull-crushing strike that killed Cheryl was apparently also
silent and bloodless. Bryan certainly did not describe a club-
bing that used “an horrendous amount of force.”

   Dr. Grey’s testimony not only cast doubt on the identity of
the murder weapon and the amount of force employed, it
clearly showed that the victims must have endured multiple
blows. Bryan’s description of a quick, three-strike attack did
not fit the physical evidence. It was more likely that the vic-
tims were struck several times than that they were each hit
once or twice (as Bryan maintained), because skulls were not
only severely fractured and fragmented, but sustained damage
on nearly every side, suggesting blows from various angles.
Cheryl Bravence’s skull showed fractures on the top and back
of the skull, breaks near the right ear, and fractures in the left
temple—hardly the work of a single silent strike to the neck.
Her husband’s skull sustained fractures at the back and top of
the head, was missing parts of bone from the left side, and
suffered breaks in the left eye socket, right brow, and left jaw.
A fracture also separated his alveolar plate—a portion of bone
that supports the upper teeth. “To inflict the extent of damage
that I see in this skull with three blows is pretty far beyond
the pale of what I would expect to be able to see,” Dr. Grey
explained. “I can’t see how that pattern would be produced by
a stick with that scenario [of three blows] that you described,
even with as much force as you could possibly muster, I don’t
see how you could get that pattern.” On cross examination,
Dr. Grey admitted that the injuries he observed could have
been caused by as few as three blows to Cheryl and four to
18314                 LANKFORD v. ARAVE
Robert—making seven strikes altogether—but more blows
would likely be needed. In addition, he explained that Bryan’s
description of the location of the blows did not match the
physical evidence. The extensive injuries on both sides of the
skulls could not have been produced during the attack Bryan
described, where an assailant struck the victims only “in the
back of the neck . . . . Not in the head.”

   Had Dr. Grey been asked to serve as an advisor in a trial
that presented this sort of forensic evidence, he would have
advised the attorney cross examining Bryan to “get [a]
detailed . . . description of how the blows were inflicted, the
number of blows, what kind of a swing was used, what the
implement, the stick, was like, [and whether] it appear[ed] to
be weighted or unweighted” so that the testimony could be
tested against the pattern of injury. Dr. Grey affirmed that his
type of questioning, together with detailed questioning of an
expert pathologist, was “the sort of thing you customarily do
when you are retained to work a case.” Dr. Grey did not dis-
agree with Dr. Cihak’s testimony at trial that the injury was
the result of blunt trauma that could have been caused by a
pipe, nightstick, rock, or a gun. The problem was that Dr.
Cihak was never “really pinned down on what [wa]s more
likely given the pattern of injury.” “He never was asked to say
among those choices what, seeing this pattern of injury, what
seems more likely . . . .” By testifying to injuries caused by
blunt trauma, Dr. Cihak merely affirmed “[a] myriad of possi-
bilities” as to the murder weapon.

   The forensic evidence, considered in light of Idaho’s cor-
roborative requirement, underscores the inconsistencies in
Bryan’s story. Bryan wavered in his physical description of
the weapon and its origin. He described the murder weapon
in ambiguous terms as a “sort of nightstick” made of wood,
“a little limb deal” and a “little club” twelve inches long. In
an interview with the sheriff, he had trouble remembering
specifics about the stick. It “could have been” a piece of pipe,
but Bryan did not know “for sure.” When asked whether the
                         LANKFORD v. ARAVE                        18315
weapon was a foot long, he said “umm, probably about, yeah,
probably about a foot and a half, maybe.” His descriptions
changed over the course of the investigation. In another of his
initial statements, given to police, he claimed that the weapon
was “a stick like a night stick that a policeman wears but only
about a foot long.” He told an FBI investigator that it was “a
‘night stick’ like a policeman uses. [Mark] had the ‘night
stick’ for a long time and carried it in his car.” On direct
examination at his own trial, Bryan said the weapon was “a
thing about a foot long, which is a little club that he has had
for a long time.” He claimed he “d[id]n’t know where [Mark]
got it from. . . . Probably bought it somewhere.” Later, at
Mark’s trial, Bryan remembered the weapon’s appearance and
history clearly. It was “a sort of a night stick, in a way . . . .
It’s about a foot long, reddish brown wood. I think it, I
believe it came from me. I believe my wife—my ex-wife gave
it to me, and I gave it to Mark a long time ago.”

   At his trial, Bryan claimed that he did not know Mark was
carrying the club when the two entered the Bravences’ camp.
“I never saw the club,” he claimed, explaining that it was so
small it could “[v]ery easily” have been concealed in a
pocket. He also said he had not seen the little club since the
killings. It could have been at the Bravences’ camp site, he
explained, or it could be at the spot where the bodies were
unloaded or the place they were ultimately hidden. “I’m sure
it would be in one of the three places,” he told the court. Mark
did in fact carry a nightstick, and it was recovered. Police
described it as a wooden nightstick, dark brown or black in
color, about eighteen inches long. The stick was not found at
the murder site, on the road, or at the Bravences’ grave site.
It was found in Mark’s abandoned car. The nightstick the
police found in Mark’s car would, of course, have been pow-
erful corroboration of Bryan’s testimony, but the state—to its
credit—declined to introduce it into evidence because it could
not be linked to the killings.5
   5
     The stick did not show any blood or tissue residue. Although the two
brothers have together given several versions of the murder story, never
did either claim to have returned to Mark’s brush-covered car after the
killings.
18316                 LANKFORD v. ARAVE
   [13] In sum, Bryan’s testimony about the murder weapon,
the number of blows, and the force of those blows was vague,
contradictory, and—when considered in light of the Bra-
vences’ fragmented skulls—not persuasive. It is this precise
scenario—an accomplice who must implicate the defendant in
order to hide his own culpability—that Idaho’s corroboration
requirement addresses. We agree with the district court that
FitzMaurice’s requested jury instructions were simply wrong
under Idaho law. The corrupted instruction was not corrected
by other instructions. Although the question is close, we dis-
agree with the district court as to the prejudicial effect of the
error. There was ample evidence that either one or both of the
Lankfords killed the Bravences, but there was no evidence
that Mark attacked and killed the Bravences other than
Bryan’s testimony, and there was strong evidence raised at the
habeas proceedings suggesting that Bryan’s testimony is
inconsistent with the forensic evidence. Counsel’s request that
the jury be instructed that it could convict on the basis of
Bryan’s testimony alone was plainly prejudicial.

                     IV.   CONCLUSION

  [14] The judgment of the district court is reversed and the
case is remanded with instructions to grant the petition for a
writ of habeas corpus, with appropriate instructions to retry
Mark Lankford within a reasonable time or release him.

  REVERSED and REMANDED.
