                       PUBLISHED


UNITED STATES COURT OF APPEALS
             FOR THE FOURTH CIRCUIT


TIMOTHY RICHARDSON,                    
             Petitioner-Appellee,
              v.
GERALD J. BRANKER, Warden,                   No. 11-1
Central Prison, Raleigh, North
Carolina,
             Respondent-Appellant.
                                       

TIMOTHY RICHARDSON,                    
               Petitioner-Appellant,
                 v.
GERALD J. BRANKER, Warden,                   No. 11-2
Central Prison, Raleigh, North
Carolina,
              Respondent-Appellee.
                                       
       Appeals from the United States District Court
   for the Eastern District of North Carolina, at Raleigh.
            Terrence W. Boyle, District Judge.
                    (5:08-hc-02163-BO)

                 Argued: December 7, 2011

                 Decided: February 6, 2012

Before TRAXLER, Chief Judge, and MOTZ and KEENAN,
                  Circuit Judges.
2                    RICHARDSON v. BRANKER
Affirmed in part, reversed in part, and remanded by published
opinion. Judge Keenan wrote the opinion, in which Chief
Judge Traxler and Judge Motz joined.


                          COUNSEL

ARGUED: Jonathan Porter Babb, Sr., NORTH CAROLINA
DEPARTMENT OF JUSTICE, Raleigh, North Carolina, for
Appellant/Cross-Appellee. Stanley F. Hammer, WYATT,
EARLY, HARRIS & WHEELER, LLP, High Point, North
Carolina, for Appellee/Cross-Appellant. ON BRIEF: Roy
Cooper, Attorney General, Raleigh, North Carolina, for
Appellant/Cross-Appellee. Kenneth J. Rose, CENTER FOR
DEATH PENALTY LITIGATION, Durham, North Carolina,
for Appellee/Cross-Appellant.


                           OPINION

BARBARA MILANO KEENAN, Circuit Judge:

   In this appeal, the State of North Carolina seeks reversal of
the district court’s judgment granting a writ of habeas corpus
to Timothy Richardson. In granting the writ, the district court
vacated the sentence of death imposed after Richardson’s con-
viction for first-degree murder. The district court concluded
that the state courts of North Carolina unreasonably applied
the Supreme Court’s holding in Strickland v. Washington, 466
U.S. 668 (1984), in rejecting Richardson’s claim that his
attorney on direct appeal failed to provide effective assistance
of counsel. The district court held that Richardson’s appellate
counsel rendered ineffective assistance by not raising on
direct appeal the state trial court’s failure to instruct the jury
at sentencing concerning the statutory mitigating factor of
Richardson’s age.
                     RICHARDSON v. BRANKER                      3
   Although the district court granted Richardson’s petition
with respect to his Strickland claim, the district court rejected
Richardson’s additional claims that he was entitled to a writ
of habeas corpus because the prosecution withheld exculpa-
tory evidence in violation of Brady v. Maryland, 373 U.S. 83
(1963) (the Brady claim), and that he was mentally retarded
and thus could not be sentenced to death following the deci-
sion in Atkins v. Virginia, 536 U.S. 304 (2002) (the Atkins
claim). Richardson has filed a cross-appeal in this Court,
asserting that the district court erred in rejecting his Brady and
Atkins claims.

   In reviewing the parties’ arguments, we are guided and
restricted by the statutory language of 28 U.S.C. § 2254, as
amended by the Antiterrorism and Effective Death Penalty
Act of 1996 (hereafter, we use the term "AEDPA" to refer to
28 U.S.C. § 2254 as amended), and a wealth of Supreme
Court precedent interpreting and applying this statute. We are
mindful that "state courts are the principal forum for asserting
constitutional challenges to state convictions," that habeas
corpus proceedings are a "guard against extreme malfunctions
in the state criminal justice systems, not a substitute for ordi-
nary error correction through appeal," and that a federal court
may only issue the writ if "there is no possibility fairminded
jurists could disagree that the state court’s decision conflicts
with [the Supreme Court’s] precedents." Harrington v. Rich-
ter, ___ U.S. ,___ 131 S. Ct. 770, 786-87 (2011) (citation and
internal quotation marks omitted).

   Upon our review, we hold that the district court’s decision
granting Richardson’s petition runs contrary to the deference
that federal courts are required to afford state court decisions
adjudicating the merits of habeas corpus claims. Accordingly,
we reverse the portion of the district court’s judgment grant-
ing Richardson’s petition on his claim of ineffective assis-
tance of counsel, and we affirm the remainder of the district
court’s judgment rejecting Richardson’s petition on his Brady
and Atkins claims.
4                      RICHARDSON v. BRANKER
                                    I.

   We briefly set forth the facts of this matter, because the
issues presented primarily involve questions of law rather
than questions of fact, and because the Supreme Court of
North Carolina previously has provided in great detail the fac-
tual background of this case. See State v. Richardson, 488
S.E.2d 148 (N.C. 1997).

                                   A.

   Timothy Richardson was convicted by a jury in 1995 of
first-degree murder and first-degree kidnapping in connection
with the death of Tracy Marie Rich.1 Id. at 151. The evidence
at trial showed that on October 6, 1993, Richardson abducted
Ms. Rich after her work shift at the L & L Food Store (the
store) in Castalia, North Carolina. Id. at 151, 157. As stated
by the Supreme Court of North Carolina, "the evidence
tended to show that [Richardson] abducted the victim from
the store, drove her to a secluded area, and ran her down with
her own car. As the victim tried to crawl away, [Richardson]
drove over her again. [Richardson] then went back to the store
to make a robbery attempt." Id. at 157. Ms. Rich’s lifeless
body was found wedged under her car. Id. at 152. The cause
of Ms. Rich’s death was "multiple blunt-force injuries and
compression injuries to her body, head, and chest as a result
of being hit by and run over with a vehicle." Id. at 153.

   Ample evidence supported the jury’s finding that Richard-
son was the perpetrator who killed Ms. Rich. The prosecution
presented the testimony of an expert in the field of forensic
fiber identification, who testified that fibers from Richard-
son’s t-shirt were consistent with fibers found on Ms. Rich’s
shirt. Id. at 153, 157. Another expert witness testified that a
    1
    The jury found Richardson guilty of first-degree murder on three sepa-
rate bases: 1) malice, premeditation, and deliberation; 2) felony murder;
and 3) lying in wait. 488 S.E.2d at 151.
                        RICHARDSON v. BRANKER                             5
shoe impression found on a piece of plasterboard inside the
store could only have been made by Richardson’s right shoe.
Id. at 152-53, 157.

   Additionally, during the course of the abduction, the store’s
alarm "tripped." Id. at 151. This caused a police officer to
come to the store, where he observed a red car that he later
learned was registered to Terry Richardson, the defendant’s
wife. Id. Police officers suspected that Richardson had partici-
pated in the crime, and they went to Richardson’s home and
arrested him after finding him hiding in the attic. Id. at 152,
157-58.

   Richardson initially denied any knowledge of Ms. Rich’s
murder, but later told police officers that he was present dur-
ing the crime while an acquaintance, Kevin Hedgepeth, killed
Ms. Rich.2 Id. at 152. The police interviewed Hedgepeth, as
well as several witnesses who provided an alibi for Hedge-
peth, and determined that Hedgepeth was not involved in Ms.
Rich’s murder. Id. at 152, 156-57. The evidence obtained dur-
ing the police investigation also discredited numerous other
aspects of Richardson’s story, rendering Richardson’s state-
ments implicating Hedgepeth implausible. Id. at 152, 157.
Hedgepeth and his alibi witnesses testified at Richardson’s
trial. Id. at 156.

   After the jury convicted Richardson of first-degree murder
and first-degree kidnapping,3 the case proceeded to the sen-
tencing phase. The jury found as aggravating circumstances
   2
     Richardson first stated that he gave Hedgepeth a ride to the store in
order for Hedgepeth to "get some money," and that Hedgepeth grabbed
Ms. Rich when she came out of the store. Id. at 152. Richardson later
amended his story, telling police that he and Hedgepeth were "dropped
off" at the store by Hedgepeth’s uncle. Id. In each of these versions of his
story, Richardson maintained that he witnessed Hedgepeth repeatedly "run
over" Ms. Rich with her car. Id. at 152.
   3
     The jury acquitted Richardson of the additional charge of robbery with
a dangerous weapon. Id. at 151.
6                       RICHARDSON v. BRANKER
that the murder was committed for pecuniary gain, and that
the murder was especially heinous, atrocious, or cruel. Id. at
160.

   The trial court instructed the jury on four statutory mitigat-
ing factors, including: (i) that the defendant had no significant
history of prior criminal activity, N.C.G.S. § 15A-2000(f)(1);
(ii) that the murder was committed while the defendant was
under the influence of mental or emotional disturbance,
N.C.G.S. § 15A-2000(f)(2); (iii) that the capacity of the
defendant to appreciate the criminality of his conduct or to
conform his conduct to the requirements of law was impaired,
N.C.G.S. § 15A-2000(f)(6); and (iv) any other circumstance
arising from the evidence which the jury deems to have miti-
gating value, N.C.G.S. § 15A-2000(f)(9) (the "catchall" miti-
gating factor). 488 S.E.2d at 160. The jury found that the first
two of these mitigating factors were applicable under the evi-
dence, but declined to find the latter two mitigating factors.4
Id. Notably, Richardson’s defense counsel did not ask for, and
the trial judge did not submit, the statutory mitigating factor
of "[t]he age of the defendant at the time of the crime,"
N.C.G.S. § 15A-2000(f)(7) (the (f)(7) mitigation instruction).5
    4
     The jury also found present several non-statutory mitigating factors,
including that: (i) the defendant’s prior criminal convictions consisted
solely of misdemeanors, and none of those prior convictions involved vio-
lence; (ii) the defendant had an IQ of 73; (iii) the defendant was addicted
to crack cocaine; (iv) at an important stage in his development, the defen-
dant suffered from the homicide of his brother, which resulted in signifi-
cant changes in the defendant’s personality and behavior; (v) the
defendant ingested lead at an early age and suffered from lead poisoning;
and (vi) the defendant had no prior history of violent conduct. Id. at 160.
   5
     North Carolina courts do not construe the term "age" solely as a per-
son’s chronological age for purposes of whether the (f)(7) mitigating
instruction should be given. Instead, "age" is a "flexible and relative con-
cept" that takes into consideration emotional maturity in addition to chro-
nological age. See State v. Johnson, 346 S.E.2d 596, 624 (N.C. 1986).
Thus, Richardson’s chronological age of 31 years at the time of the
offense would not have foreclosed the availability of the (f)(7) mitigation
instruction.
                       RICHARDSON v. BRANKER                            7
   After balancing the mitigating and aggravating circum-
stances, the jury recommended a sentence of death. 488
S.E.2d at 151, 160. The trial court followed the jury’s recom-
mendation and sentenced Richardson to death, in addition to
a sentence of forty years’ imprisonment for the first-degree
kidnapping conviction. Id. at 151.

                                   B.

   Richardson filed an appeal with the Supreme Court of
North Carolina, in which his appellate counsel raised six
guilt-phase issues, and one sentencing-phase issue challeng-
ing the proportionality of Richardson’s death sentence. Rich-
ardson’s appellate counsel did not raise as error the state trial
court’s failure to instruct the jury on the (f)(7) mitigation fac-
tor. The Supreme Court of North Carolina affirmed Richard-
son’s convictions and sentences. Id. at 162.

   In March 1999, Richardson filed a Motion for Appropriate
Relief in the Superior Court of Nash County, North Carolina
(the MAR court), seeking to vacate his convictions and sen-
tences. In his motion, Richardson raised numerous claims,
including claims regarding the effectiveness of his trial coun-
sel, the effectiveness of his appellate counsel, and the State’s
purported withholding of certain exculpatory evidence. Rich-
ardson later filed two amended Motions for Appropriate
Relief, adding a second category of allegedly exculpatory evi-
dence withheld by the State, as well as a claim that he was
mentally retarded and thus could not be executed under state
and federal law.6

  Richardson’s argument of ineffective assistance of appel-
  6
   Richardson raised the claim that he was mentally retarded and could
not be executed before the Supreme Court issued its decision in Atkins, in
which the Court held that the execution of mentally retarded individuals
violated the Eighth Amendment’s prohibition against cruel and unusual
punishments. 536 U.S. 304.
8                       RICHARDSON v. BRANKER
late counsel was based on his appellate counsel’s failure to
argue that the trial court should have submitted the (f)(7) miti-
gation instruction to the jury. In support of this argument,
Richardson submitted the affidavit of his appellate counsel,
who averred that he "was aware that [Richardson’s] mental
age was that of [sic] eleven and one-half or twelve years old
and that his I.Q. was 73," but that "[t]he law regarding this
mitigating factor [was] not clarified until after [Richardson’s]
trial."7

   The MAR court adjudicated the merits of Richardson’s
claims and denied them.8 With respect to the (f)(7) mitigation
instruction issue, the MAR court held as follows:

        (f) As to [Richardson’s] allegation of ineffective
        assistance of appellate counsel this Court again looks
        to the decisions in Strickland and [State v.] Braswell,
        [312 N.C. 553 (1984)] [.]

        (g) That this Court finds as a fact in review of this
        claim that this claim is without merit. [Richardson]
        has failed to establish that his appellate counsel’s
    7
     In the affidavit, Richardson’s appellate counsel also averred that "I do
not recall ever giving significant consideration to raising this issue,
because absent a request for this instruction, review would likely have
been under the plain error standard." We observe that Richardson’s appel-
late counsel’s statement, that the plain error standard of review would
have applied to this claim had it been raised on appeal for the first time,
is incorrect as a matter of law. See State v. Holden, 450 S.E.2d 878, 885
(N.C. 1994) (holding that, irrespective whether the defendant’s attorney
requests an (f)(7) mitigation instruction, the trial court has an "independent
duty" to submit the instruction if it is warranted by the evidence); see also
State v. Spruill, 452 S.E.2d 279, 305 (N.C. 1994) (considering, without
mention of the plain error standard of review, defendant’s argument con-
cerning the (f)(7) mitigation instruction despite defendant’s failure to
request that the instruction be given to the jury).
   8
     The MAR court did not consider the merits of several claims that the
court held were procedurally barred, but none of those claims is at issue
on this appeal.
                    RICHARDSON v. BRANKER                     9
    representation fell below an objective standard of
    reasonableness. This Court further finds that there is
    no reasonable probability that in the absence of
    appellate counsel’s alleged errors the results of the
    proceedings would have been different.

    (h) The Court also finds that no evidentiary hearing
    is required in that [Richardson’s] allegation of inef-
    fective assistance of appellate counsel involves a
    question of law and not fact.

    (i) The Court also finds, upon full review of this
    claim, that if [Richardson’s] allegations were indeed
    errors, and this Court specifically finds no errors,
    such errors would be harmless beyond a reasonable
    doubt.

   The MAR court also rejected Richardson’s argument that
the State withheld from him certain exculpatory evidence, in
violation of Brady. The MAR court held that Richardson’s
Brady claim was procedurally barred, but also held alterna-
tively on the merits that there were no errors with respect to
this issue, and that, even if there were errors, they "were
harmless beyond a reasonable doubt." The MAR court further
held that "the Court finds as a fact that there is no reasonable
possibility that, had the alleged error in question not been
committed, a different result would have been reached at the
trial."

   With respect to Richardson’s claim that he was mentally
retarded and could not be executed without violating the
Eighth and Fourteenth Amendments, the MAR court initially
deferred ruling on the claim and ordered an evidentiary hear-
ing. At the hearing, the parties introduced the testimony of
their respective mental health experts. After considering this
evidence, the MAR court entered an order denying the mental
retardation claim. The MAR court’s order, issued after the
Supreme Court decided Atkins, included numerous findings of
10                   RICHARDSON v. BRANKER
fact supporting the MAR court’s conclusion. After setting
forth its factual findings, the MAR court held:

     [Richardson] has experienced some difficulty in the
     area of adaptive functioning, but [ ] he is not signifi-
     cantly impaired in his adaptive functioning as
     required by [N.C.G.S. §] 15A-2002. The Court also
     finds that there is some evidence that [Richardson]
     suffers some reduced mental capacity, but that he is
     not mentally retarded as set out in [N.C.G.S. §] 15A-
     2005. The Court further finds that the defendant has
     failed to meet the burden of proof requiring the
     defendant to show that he has significantly sub aver-
     age adaptive skills in at least two areas as set out in
     the General Statutes of North Carolina. The defen-
     dant has also failed to show that he suffers from
     Mental Retardation as required by [N.C.G.S. §] 15A-
     2005.

   After the MAR court denied Richardson’s claims, Richard-
son filed a petition for a writ of certiorari in the Supreme
Court of North Carolina. That court denied Richardson’s peti-
tion. 667 S.E.2d 272 (N.C. 2008).

                               C.

   In November 2008, Richardson filed a petition for a writ of
habeas corpus (the habeas petition) in the United States Dis-
trict Court for the Eastern District of North Carolina, naming
as respondent Gerald Branker, the warden of Central Prison
located in Raleigh, North Carolina (hereafter, the State). Rich-
ardson argued that the MAR court’s denial of his motion for
appropriate relief was based on an unreasonable determina-
tion of facts and application of United States Supreme Court
precedent. Richardson raised four grounds for relief in his
petition, including that: (1) the State withheld exculpatory
evidence in violation of Brady that would have corroborated
Richardson’s theory that his acquaintance, Kevin Hedgepeth,
                    RICHARDSON v. BRANKER                     11
murdered Ms. Rich; (2) his trial counsel rendered ineffective
assistance by not moving to suppress certain statements Rich-
ardson made while in police custody; (3) Richardson’s appel-
late counsel rendered ineffective assistance by not raising as
error the trial court’s failure to provide the jury at sentencing
the (f)(7) mitigation instruction; and (4) he is mentally
retarded and therefore his death sentence violates the Eighth
Amendment, under the Supreme Court’s decision in Atkins.
The State answered the habeas petition, and filed a motion for
summary judgment.

   The district court granted Richardson a writ of habeas cor-
pus with respect to his claim that he received ineffective assis-
tance of appellate counsel. 769 F. Supp. 2d 896, 928
(E.D.N.C. 2011). The district court held that North Carolina
law mandates that a trial court submit for the jury’s consider-
ation any statutory mitigating factor that is supported by sub-
stantial evidence, even if the defendant does not make such a
request. Id. at 919 (citing N.C.G.S. § 15A-2000(b) and State
v. Holden, 450 S.E.2d 878, 885 (N.C. 1994)). Without
addressing the decision in State v. Spruill, 452 S.E.2d 279
(N.C. 1994), the primary case relied upon by the State that
sets forth a legal standard seemingly irreconcilable with the
decision in Holden, the district court concluded that "North
Carolina law supporting petitioner’s claim was established
months before petitioner’s trial and well before his appeal."
Id. at 921.

   Stating that it was "considering the issue de novo," id. at
924, the district court set forth the evidence presented by
Richardson that "[h]is overall functioning would be compara-
ble to that of an average eleven-and-a-half, twelve year old,"
and that he suffered from alcohol and drug abuse, mild neuro-
cognitive disorder, personality disorder, and borderline mental
retardation. Id. at 920, 922. Based on its consideration of
Richardson’s evidence, the district court held that appellate
counsel’s failure to challenge as error the absence of a (f)(7)
mitigation instruction was unreasonable. Id. at 921. Addition-
12                  RICHARDSON v. BRANKER
ally, relying on the decision in Holden, as well as on the deci-
sion in State v. Zuniga, 498 S.E.2d 611 (N.C. 1998), an appeal
decided well after Richardson’s appeal was argued, the dis-
trict court held that "had counsel raised the [(f)(7) mitigation
instruction] issue on appeal, there is a reasonable probability
petitioner would have prevailed." Id. at 921-22. The district
court further concluded that "the State is unable to show the
error likely would have been found to be harmless beyond a
reasonable doubt on appeal." Id. at 922.

   Because the district court considered Richardson’s ineffec-
tive assistance of counsel claim de novo, the court did not
accord any deference to the MAR court’s resolution of this
claim. The only reference to the MAR court in this section of
the district court’s analysis is the conclusion that "[t]he
[MAR] court’s determination to the contrary is based on an
unreasonable determination of the facts and an unreasonable
application of Smith v. Robbins[, 528 U.S. 259 (2000),] and
Strickland." 769 F. Supp. 2d at 924.

   The district court ordered that Richardson be sentenced to
a term of life imprisonment unless the State initiated new sen-
tencing proceedings within 180 days of the district court’s
order. Id. at 928. With respect to Richardson’s claim of inef-
fective assistance of trial counsel, his Atkins claim, and his
Brady claim, the district court granted the State’s motion for
summary judgment, holding that Richardson failed to estab-
lish that he was entitled to a writ of habeas corpus on those
claims. Id. at 908-19, 924-28.

   The State timely filed a notice of appeal to the district
court’s grant of the habeas petition on Richardson’s claim of
ineffective assistance of appellate counsel. Richardson filed
an application for a certificate of appealability regarding the
claims that were denied by the district court. The district court
granted the application in part and denied it in part, granting
the certificate with respect to Richardson’s Brady and Atkins
claims.
                       RICHARDSON v. BRANKER                          13
                                   II.

                                   A.

                                   i.

   We first address the district court’s decision granting a writ
of habeas corpus to Richardson on his claim of ineffective
assistance of appellate counsel. We review de novo the dis-
trict court’s order granting Richardson relief on this claim.
Kanai v. McHugh, 638 F.3d 251, 260 (4th Cir. 2011).

   AEDPA governs federal courts’ consideration of a state
prisoner’s petition for a writ of habeas corpus. The standard
set forth by AEDPA (the AEDPA standard) mandates that a
writ of habeas corpus "shall not be granted" for any claim that
was adjudicated on the merits in a state court proceeding
unless the state court’s adjudication:

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

      (2) resulted in a decision that was based on an unrea-
      sonable determination of the facts in light of the evi-
      dence presented in the State court proceeding.9

28 U.S.C. § 2254(d); Harrington, 131 S. Ct. at 785; DeCastro
v. Branker, 642 F.3d 442, 449 (4th Cir. 2011).

  The limited scope of federal review of a state petitioner’s
  9
   Richardson does not dispute that the MAR court adjudicated the merits
of his claim of ineffective assistance of appellate counsel. We also note
that our analysis primarily applies the first prong of the AEDPA standard
because Richardson’s arguments concern issues of law, rather than factual
determinations.
14                  RICHARDSON v. BRANKER
habeas claims, as established by AEDPA, is grounded in fun-
damental notions of state sovereignty. Harrington, 131 S. Ct.
at 787. When a federal court adjudicates a habeas corpus peti-
tion brought by a state prisoner, that adjudication constitutes
an intrusion on state sovereignty. See id. ("Federal habeas
review of state convictions . . . intrudes on state sovereignty
to a degree matched by few exercises of federal judicial
authority.") (Citation omitted). However, AEDPA restricts
that intrusion of state sovereignty by limiting the federal
courts’ power to issue a writ to exceptional circumstances,
thereby helping to ensure that "state proceedings are the cen-
tral process, not just a preliminary step for a later federal
habeas proceeding." Id. The restrictive standard of review
established by AEDPA "further[s] the principles of comity,
finality, and federalism." Williams v. Taylor, 529 U.S. 362,
436 (2000).

   The Supreme Court’s recent decision in Harrington, which
also involved a habeas claim alleging ineffective assistance of
counsel, is instructive regarding the significant deference that
federal courts must accord to state court decisions adjudicat-
ing habeas corpus claims on their merits. As the Supreme
Court observed, "[t]he pivotal question is whether the state
court’s application of the [applicable federal legal] standard
was unreasonable." 131 S. Ct. at 785 (emphasis added).

   Fundamentally, "‘an unreasonable application of federal
law is different from an incorrect application of federal law.’"
Id. (quoting Williams, 529 U.S. at 410) (emphasis in original).
The standard of an "unreasonable" application of federal law
requires a "substantially higher threshold" to obtain relief than
the standard of an "incorrect" application of federal law.
Schriro v. Landrigan, 550 U.S. 465, 473 (2007). "[S]o long
as ‘fairminded jurists could disagree on the correctness of [a]
state court’s decision,’" a state court’s adjudication that a
habeas claim fails on its merits cannot be overturned by a fed-
eral court. Harrington, 131 S. Ct. at 786 (quoting Yarborough
v. Alvarado, 541 U.S. 652, 664 (2004)). Thus, "even a strong
                         RICHARDSON v. BRANKER                              15
case for relief does not mean the state court’s contrary conclu-
sion was unreasonable." Id. at 786 (citing Lockyer v. Andrade,
538 U.S. 63, 75 (2003)).

   Accordingly, Richardson had the burden of establishing
that the MAR court’s decision "was so lacking in justification
that there was an error well understood and comprehended in
existing law beyond any possibility for fairminded disagree-
ment." Id. at 786-87. As stated by the Supreme Court, this is
a standard that "is difficult to meet . . . because it was meant
to be." Id. at 786.

   Additionally, when a petitioner’s habeas corpus claim is
based on alleged ineffective assistance of counsel, we review
the claim through the additional lens of Strickland and its
progeny, as discussed below. The AEDPA standard and the
Strickland standard are dual and overlapping, and we apply
the two standards simultaneously rather than sequentially. See
Harrington, 131 S. Ct. at 788. This imposes a very high bur-
den for a petitioner to overcome, because these standards are
each "highly deferential" to the state court’s adjudication and,
"when the two apply in tandem, review is doubly so." Id.
(citations and internal quotation marks omitted).

   To prevail on a claim of ineffective assistance of counsel,10
a petitioner ordinarily must satisfy both parts of the two-part
test set forth in Strickland. Wiggins v. Smith, 539 U.S. 510,
521 (2003); Williams, 529 U.S. at 390; Strickland, 466 U.S.
at 687; Jackson v. Kelly, 650 F.3d 477, 493 (4th Cir. 2011).
  10
    As the Supreme Court explained in Strickland, the Sixth Amend-
ment’s guarantee of "‘the right to counsel is the right to the effective assis-
tance of counsel.’" 466 U.S. at 686 (quoting McMann v. Richardson, 397
U.S. 759, 771 n.14 (1970)). Although Strickland involved a claim con-
cerning the alleged ineffective assistance of the defendant’s trial counsel,
the right to effective assistance of appellate counsel, as well as the Strick-
land standard for evaluating an ineffective assistance of counsel claim,
was extended to appellate proceedings in Smith v. Murray, 477 U.S. 527
(1986), and Smith v. Robbins, 528 U.S. 259 (2000).
16                  RICHARDSON v. BRANKER
The petitioner first must show that "counsel’s representation
fell below an objective standard of reasonableness." Strick-
land, 466 U.S. at 687–88; accord Wiggins, 539 U.S. at 521;
Williams, 529 U.S. at 390–91; Sharpe v. Bell, 593 F.3d 372,
382 (4th Cir. 2010). In making this determination, a court
considering the habeas corpus petition "must indulge a strong
presumption that counsel’s conduct falls within the wide
range of reasonable professional assistance." Strickland, 466
U.S. at 689; accord Kimmelman v. Morrison, 477 U.S. 365,
381 (1986); Darden v. Wainwright, 477 U.S. 168, 185–86
(1986); United States v. Tucker, 603 F.3d 260, 264 (4th Cir.
2010).

   If counsel’s performance is found to have been deficient
under the first part of the Strickland standard, to obtain relief
the petitioner must also show that "there is a reasonable prob-
ability that, but for counsel’s unprofessional errors, the result
of the proceeding would have been different." Strickland, 466
U.S. at 694; accord Wiggins, 539 U.S. at 534; Williams, 529
U.S. at 391; Gray v. Branker, 529 F.3d 220, 234 (4th Cir.
2008). "A reasonable probability is a probability sufficient to
undermine confidence in the outcome," Strickland, 466 U.S.
at 694, and "[t]he likelihood of a different result must be sub-
stantial, not just conceivable," Harrington, 131 S. Ct. at 792
(emphasis added); accord Jackson, 650 F.3d at 493.

   In the context of a claim of ineffective assistance of appel-
late counsel, the "proceeding" at issue is the forum in which
the petitioner’s appeal was heard, which in this case was the
Supreme Court of North Carolina. See Smith v. Robbins, 528
U.S. 259, 285-86 (2000) (holding, in the context of an ineffec-
tive assistance of appellate counsel claim, that the "prejudice"
element of the Strickland standard is satisfied by a showing
of a reasonable probability defendant would have prevailed on
appeal but for appellate counsel’s deficient performance); Bell
v. Jarvis, 236 F.3d 149, 164 (4th Cir. 2000) (en banc) (same).
Therefore, for purposes of Strickland’s "prejudice" prong, as
applied in tandem with the AEDPA standard, Richardson
                       RICHARDSON v. BRANKER                            17
must demonstrate that the MAR court incorrectly and unrea-
sonably concluded that Richardson failed to demonstrate there
was a "reasonable probability" the Supreme Court of North
Carolina would have held in his favor had his appellate coun-
sel raised the issue of the (f)(7) mitigation instruction in the
direct appeal.

                                    ii.

   As an initial matter, we conclude that the district court
erred in considering Richardson’s Strickland claim under a de
novo standard of review. In a manner almost identical to the
Ninth Circuit’s error in Harrington, the district court explic-
itly conducted a de novo review, concluded that Richardson’s
counsel rendered ineffective assistance under Strickland, and
stated in a conclusory manner that "[t]he MAR court’s deter-
mination to the contrary is based on an unreasonable determi-
nation of the facts and an unreasonable application of
[Strickland]."11 769 F. Supp. 2d at 924. However, as the
Supreme Court stated in Harrington, "AEDPA demands
more."12 131 S. Ct. at 786; see also Bell, 236 F.3d at 157 (rec-
ognizing that federal courts may not conduct de novo review
of habeas corpus claims that were adjudicated on the merits
by a state court).

   In holding that the Ninth Circuit erred in considering Har-
rington’s habeas corpus petition de novo, the Supreme Court
provided further instruction concerning federal courts’ duties
  11
      In Harrington, the Supreme Court observed that the Ninth Circuit "ex-
plicitly conducted a de novo review, and after finding a Strickland viola-
tion, it declared, without further explanation, that the ‘state court’s
decision to the contrary constituted an unreasonable application of Strick-
land.’" 131 S. Ct. at 786 (internal citation omitted).
   12
      We observe that, before AEDPA’s enactment in 1996, federal courts
were required to exercise independent judgment when reviewing a state
prisoner’s application for habeas relief. See Bell v. Jarvis, 236 F.3d 149,
159-60 (4th Cir. 2000) (en banc) (discussing Williams v. Taylor, 529 U.S.
362, 399-401 (2000) (O’Connor, J., concurring)).
18                  RICHARDSON v. BRANKER
when considering a habeas corpus claim. The Supreme Court
emphasized that, under AEDPA,

     a habeas court must determine what arguments or
     theories supported or, as here, could have supported,
     the state court’s decision; and then it must ask
     whether it is possible fairminded jurists could dis-
     agree that those arguments or theories are inconsis-
     tent with the holding in a prior decision of this
     Court.

Harrington, 131 S. Ct. at 786. In short, AEDPA "demands
that state court decisions be given the benefit of the doubt."
Woodford v. Visciotti, 537 U.S. 19, 24 (2002) (per curiam).

   We turn to apply this method of analysis to Richardson’s
claim of ineffective assistance of appellate counsel. We
remain mindful of the Supreme Court’s statement in Strick-
land that a reviewing court is not required to address the issue
whether "counsel’s performance was deficient before examin-
ing the prejudice suffered by the defendant as a result of the
alleged deficiencies." 466 U.S. at 697. As instructed by the
Court, "[i]f it is easier to dispose of an ineffectiveness claim
on the ground of lack of sufficient prejudice, which we expect
will often be so, that course should be followed." Id.; see also
Buckner v. Polk, 453 F.3d 195, 202 (4th Cir. 2006) (following
Supreme Court’s instruction in Strickland to proceed directly
to "prejudice" prong if petitioner cannot demonstrate reason-
able probability that outcome of trial would be different but
for counsel’s performance). Accordingly, we address Richard-
son’s claim of ineffective assistance of appellate counsel
under the "prejudice" prong of Strickland.

  Under the dual, overlapping lenses of AEDPA and Strick-
land, we ask the following question: Was the MAR court’s
holding that "there is no reasonable probability that in the
absence of appellate counsel’s alleged errors the results of the
proceedings would have been different" incorrect to a degree
                     RICHARDSON v. BRANKER                     19
that this conclusion "was so lacking in justification that [it]
was an error well understood and comprehended in existing
law beyond any possibility for fairminded disagreement?" See
Harrington, 131 S. Ct. at 786-87.

   Central to our consideration of this question is the district
court’s conclusion that, at the time of Richardson’s direct
appeal, settled North Carolina law mandated that trial courts
submit to the jury any statutory mitigating factor that was sup-
ported by substantial evidence. See 769 F. Supp. 2d at 919,
921. The district court held that, therefore, there was a "rea-
sonable probability [Richardson] would have prevailed on
appeal had the [(f)(7) mitigation instruction issue] been
raised." Id. at 921, 924.

   We disagree with the district court’s holding for several
reasons. First, the district court erred in not affording any def-
erence to the MAR court’s contrary conclusion. When a claim
of ineffective assistance of counsel raised in a habeas corpus
petition involves an issue unique to state law, such as the
availability of the (f)(7) mitigation instruction at issue here, a
federal court should be especially deferential to a state post-
conviction court’s interpretation of its own state’s law.
Indeed, we have held that "[i]t is beyond the mandate of fed-
eral habeas courts [ ] to correct the interpretation by state
courts of a state’s own laws." Sharpe v. Bell, 593 F.3d 372,
383 (4th Cir. 2010) (citing Estelle v. McGuire, 502 U.S. 62,
67-68 (1991)) (additional citation omitted); see also Wood-
ford, 537 U.S. at 24 (under AEDPA, state court decisions
must be given the benefit of the doubt). This required defer-
ence to the MAR court’s adjudication of Richardson’s claim
of ineffective assistance of appellate counsel was wholly lack-
ing in the district court’s consideration of the habeas petition.

  Second, when viewed under the applicable AEDPA stan-
dard, it is manifest that Richardson failed to establish that the
MAR court’s decision was "so lacking in justification that [it]
was an error well understood and comprehended in existing
20                     RICHARDSON v. BRANKER
law beyond any possibility for fairminded disagreement." See
Harrington, 131 S. Ct. at 786-87. Moreover, we conclude that
the law regarding the circumstances in which a North Caro-
lina trial court must submit the (f)(7) mitigation instruction to
the jury was not settled at the time of Richardson’s appeal. As
discussed below, the unsettled nature of North Carolina law
on this issue precludes a finding that Richardson demon-
strated a "reasonable probability" that he would have pre-
vailed on his direct appeal had his appellate counsel raised the
(f)(7) mitigation instruction issue.

   The district court, relying on the decision in Holden, 450
S.E.2d 878, wholly failed to consider the contrary holding of
Spruill, 452 S.E.2d 279, another case involving the (f)(7) mit-
igation instruction decided by the Supreme Court of North
Carolina three weeks after the decision in Holden. In Holden,
the Supreme Court of North Carolina held that a trial court
has an independent duty to submit the (f)(7) statutory mitigat-
ing factor to the jury whenever "substantial evidence" sup-
ports that factor. 450 S.E.2d at 885. The court accordingly
applied this "substantial evidence" standard, holding that
although Holden was thirty-years old at the time of his
offense, the (f)(7) mitigation instruction should have been
given to the jury because he presented evidence that he had
(1) an I.Q. score of 56, in the mentally retarded range, and (2)
a "mental age" of ten years.13 Id. at 882, 885.

   In Spruill, however, the Supreme Court of North Carolina
rejected the defendant’s argument that the trial court erred in
failing to submit the (f)(7) mitigation instruction to the jury,
despite Spruill’s evidence that he was "emotionally imma-
ture," had I.Q. scores of 64 and 74, placing him in either the
range of mild mental retardation or the "low borderline range
of intellectual functioning," had personality disorders, and
  13
    The court held that the instruction should have been given despite evi-
dence that Holden "had more life experience than a ten-year-old-child."
450 S.E.2d at 885.
                        RICHARDSON v. BRANKER                            21
read at a level below the sixth grade. 452 S.E.2d at 284-86,
305. Notably, the decision in Spruill did not cite Holden or
apply the "substantial evidence" standard used in that case.

   Instead, in Spruill, the Supreme Court of North Carolina
applied a "counterbalancing evidence" standard, considering
evidence of the defendant’s "more mature qualities and charac-
teristics."14 Id. at 305 (citation omitted). The court held that
"[w]here evidence of emotional immaturity is counterbal-
anced by a chronological age of [thirty-one] years, apparently
normal physical and intellectual development, and experience,
the trial court is not required to submit the mitigating circum-
stance of age." Id. (citing State v. Johnson, 346 S.E.2d 596
(N.C. 1986)) (emphasis added).

   We conclude that the "substantial evidence" standard, as set
forth in Holden, and the "counterbalancing evidence" stan-
dard, as articulated in Spruill, are diametrically conflicting. It
is difficult to predict which of these two standards would have
been applied by the Supreme Court of North Carolina had
Richardson’s appellate counsel raised the (f)(7) mitigation
instruction issue on direct appeal.15 Application of these dif-
  14
      The court observed that Spruill was "thirty-one years old, had worked
as an automobile mechanic and in a shipyard, moved on to a better posi-
tion, attended church, and functioned quite well in the community." 452
S.E.2d at 305.
   15
      The Supreme Court of North Carolina ultimately may have applied
Spruill’s "counterbalancing evidence" standard, because that standard has
been applied by that Court in several more recent cases. See, e.g., State v.
Hurst, 624 S.E.2d 309, 323-25 (N.C. 2006) (applying Spruill’s "counter-
balancing evidence" standard in rejecting defendant’s argument that he
was entitled to a (f)(7) mitigating instruction); State v. Thompson, 604
S.E.2d 850, 867-68 (N.C. 2004) (same); State v. Call, 545 S.E.2d 190,
198-99 (N.C. 2001) (same); State v. Steen, 536 S.E.2d 1, 18-20 (N.C.
2000) (same); State v. Meyer, 540 S.E.2d 1, 6 (N.C. 2000) (same). In con-
trast, we have found only two decisions in which the Supreme Court of
North Carolina applied Holden’s "substantial evidence" standard. See
State v. Zuniga, 498 S.E.2d 611, 612-13 (N.C. 1998) (applying Holden’s
22                       RICHARDSON v. BRANKER
ferent standards may well have yielded different results under
the facts of this case. For instance, Richardson’s evidence that
he had I.Q. scores of 73 and 74, and had a "mental age" and
"overall functioning" comparable to an average eleven-and-a-
half or twelve-year-old, may have been sufficient to require
submission of the mitigation instruction under Holden’s "sub-
stantial evidence" test.

   Here, however, the State developed "counterbalancing" evi-
dence suggesting that Richardson displayed the socially adap-
tive behavior of an adult. The evidence of such behavior
includes Richardson’s involvement in a 10-year marriage, his
ability to maintain good, loving relationships with his wife
and daughter, and Richardson’s significant employment histo-
ry.16 Additionally, Richardson’s own witness, Dr. John Gor-
man, who qualified as an expert in the field of clinical
psychology, testified that Richardson did not display "excess
anger, hostility, or grudges." The inclusion of this evidence
presented by the State, when viewed under Spruill’s "counter-
balancing evidence" standard, likely would have supported
the absence of an (f)(7) mitigation instruction in this case.17

"substantial evidence" standard in holding trial court erred in not submit-
ting (f)(7) mitigating instruction); State v. Hooks, 548 S.E.2d 501, 509
(N.C. 2001) (applying Holden’s "substantial evidence" standard but hold-
ing trial court did not err in failing to submit the (f)(2) mitigating factor
that defendant committed the crime under the influence of mental or emo-
tional disturbance).
   16
      The evidence showed that Richardson was able to maintain steady
employment. He worked for a textile plant for about two years, and later
worked for his father’s brick-washing business four or five days per week.
   17
      There is a suggestion that the district court considered the "counterbal-
ancing evidence" standard, albeit without citing Spruill in the course of
that discussion. The district court stated that "[w]hen factors such as peti-
tioner’s chronological age, life experience, and intellectual development
are considered, they do not counterbalance the substantial evidence of
petitioner’s young mental age." 769 F. Supp. 2d at 922. We disagree with
this conclusion, which, in any event, completely fails to afford the defer-
ence required by AEDPA to the MAR court’s holding.
                        RICHARDSON v. BRANKER                              23
   The plain and irreconcilable conflict presented by the
Holden and Spruill standards demonstrates that North Caro-
lina law was not settled with respect to this issue at the time
of Richardson’s appeal. Thus, given the AEDPA standard that
we apply in tandem with the standard set forth in Strickland,
we need only return to our original question: Was the MAR
court’s holding that "there is no reasonable probability that in
the absence of appellate counsel’s alleged errors the results of
the proceedings would have been different" incorrect to a
degree that this conclusion "was so lacking in justification
that [it] was an error well understood and comprehended in
existing law beyond any possibility for fairminded disagree-
ment?" In this case, as we have observed, an application of
the "counterbalancing evidence" standard from Spruill to the
similar evidence found in the present record could well have
supported the MAR court’s decision denying Richardson
relief on his claim of ineffective assistance of appellate coun-
sel. Accordingly, the answer to the question posed above is
"no."

   Our conclusion is not altered by Richardson’s attempt to
distinguish the holding in Spruill from the facts of this case.
According to Richardson, the decision in Holden applies here
rather than the decision in Spruill, because there was no testi-
mony in Spruill correlating the defendant’s mental develop-
ment to his age, whereas, in this case and in Holden, there
was such correlating testimony. However, Richardson does
not cite any North Carolina case holding that the presence of
such "correlating testimony" requires submission of the (f)(7)
mitigation instruction, nor could we find any such case.18
Richardson’s argument therefore is not clearly supported by
existing North Carolina law and, accordingly, we are required
to reject that argument under the dual lens of the AEDPA and
Strickland standards that we apply.
  18
    Moreover, we observe that in Spruill, the defendant had I.Q. scores of
64 and 73, and "read at the 5.5 grade level," facts that suggest on their face
that the defendant was emotionally and intellectually immature despite a
chronological age of 31 years. 452 S.E.2d at 285, 305.
24                      RICHARDSON v. BRANKER
   Because we conclude that the MAR court did not hold
unreasonably that Richardson failed to demonstrate "preju-
dice" under Strickland, we need not address the MAR court’s
conclusions that the performance of Richardson’s appellate
counsel was satisfactory or that any error, if committed, was
harmless. See Strickland, 466 U.S. at 697; Buckner, 453 F.3d
at 202. Accordingly, we reverse the district court’s grant of a
writ of habeas corpus to Richardson on his claim that his
appellate counsel rendered ineffective assistance in violation
of the Sixth Amendment.

                                    B.

   We next address Richardson’s argument that the MAR
court erred in denying him relief on the basis that the State
withheld exculpatory evidence from him before trial, in viola-
tion of Brady. The district court declined to grant Richardson
relief on this claim, and we review the district court’s decision
de novo. Muhammad v. Kelly, 575 F.3d 359, 367 (4th Cir.
2009). We examine Richardson’s argument through the dual
lens of the AEDPA standard and the standard set forth by the
Supreme Court in Brady.19
  19
     The district court reviewed Richardson’s Brady claim de novo "in an
abundance of caution," reasoning that it was unclear whether the MAR
court ruled on both aspects of Richardson’s Brady claim or on only one
of the categories of evidence that Richardson alleges was withheld in vio-
lation of Brady. 769 F. Supp. 2d at 908. We hold that the district court
erred in reviewing the Brady claim de novo. Although the MAR court did
not specifically mention either category of evidence in rejecting the claim,
instead referring generically to the alleged "withheld exculpatory evi-
dence," any doubts concerning the breadth of the MAR court’s holding
must be resolved in favor of the State. See Harrington, 131 S. Ct. at 784-
85 ("When a federal claim has been presented to a state court and the state
court has denied relief, it may be presumed that the state court adjudicated
the claim on the merits in the absence of any indication or state-law proce-
dural principles to the contrary."). We cannot discern from the MAR
court’s decision any indication that the court failed to consider both cate-
gories of evidence in rejecting Richardson’s Brady claim. Accordingly,
the district court should have analyzed this claim under the deferential
standard set forth in AEDPA.
                    RICHARDSON v. BRANKER                     25
   In Brady, the Supreme Court held that a due process viola-
tion occurs when the prosecution suppresses evidence favor-
able to an accused that is material either to guilt or to
punishment, irrespective whether the prosecution acted in
good faith. 373 U.S. at 87; see also Strickler v. Greene, 527
U.S. 263, 280 (1999); Kyles v. Whitley, 514 U.S. 419, 432
(1995); United States v. King, 628 F.3d 693, 701 (4th Cir.
2011). Such evidence is "material" if there is a reasonable
probability that the proceeding would have resulted in a dif-
ferent outcome had the evidence been disclosed to the
defense. Strickler, 527 U.S. at 280; Kyles, 514 U.S. at 433;
United States v. Bagley, 473 U.S. 667, 682 (1985); see also
King, 628 F.3d at 702. Like the use of the term "reasonable
probability" in the context of Strickland, a "reasonable proba-
bility" under Brady is one that is sufficient to undermine con-
fidence in the outcome of the proceeding. Kyles, 514 U.S. at
434; Bagley, 473 U.S. at 682. At the heart of this inquiry is
a determination whether the favorable evidence withheld from
the defendant reasonably could be considered as placing the
entire case in such a different light that confidence in the ver-
dict is undermined. Strickler, 527 U.S. at 290; Kyles, 514 U.S.
at 435; King, 628 F.3d at 704.

   Richardson argues that the State withheld two pieces of
evidence that he contends are material. First, Richardson
asserts that the State withheld sketches of shoe prints drawn
from a ceiling tile taken from the crime scene. According to
Richardson, the sketches show a pattern consistent with shoes
belonging to Hedgepeth, thus bolstering Richardson’s claim
that Hedgepeth was present during the commission of the
crime. Second, Richardson asserts that the State withheld out-
of-court statements made by a testifying witness in which the
witness stated that she saw Hedgepeth with Richardson on
three occasions on the day of the crime. Although we initially
address this evidence on an item-by-item basis, our determi-
nation whether the withheld evidence was "material" ulti-
mately must be made by considering its cumulative effect. See
26                  RICHARDSON v. BRANKER
Kyles, 514 U.S. at 436 n.10; United States v. Ellis, 121 F.3d
908, 916 (4th Cir. 1997).

                               i.

   We first consider the ceiling tile sketches that Richardson
claims are exculpatory. Joyce Petzka, an Agent with the North
Carolina State Bureau of Investigations (SBI), examined two
pieces of tile found at the crime scene. The first piece of tile,
labeled "item 6," was found on the floor of the store. Agent
Petzka testified at trial that item 6 bore a shoe impression that
matched shoes seized from Richardson.

   Agent Petzka also examined a piece of ceiling tile recov-
ered from the store labeled as "item 41," which the State inad-
vertently discarded before Richardson’s counsel had an
opportunity to examine it. She testified that item 41 "had sev-
eral small portions of questioned footwear impressions; how-
ever, these impressions were very faint and they were not
sufficient for comparison purposes." During cross-
examination, Agent Petzka stated that the shoe impression
contained on item 41 was not consistent with the shoes worn
by Richardson on the night of the crime.

   Unbeknownst to Richardson, however, Agent Petzka had
drawn sketches of item 41. Richardson first received these
sketches during the state post-conviction proceedings. These
sketches showed a "zigzag" pattern that Richardson con-
tended was consistent with the pattern of Hedgepeth’s shoes.

   Richardson unsuccessfully raised this issue in the MAR
court as part of his Brady claim. The MAR court held that
"there is no reasonable possibility that, had the alleged error
in question not been committed, a different result would have
been reached at trial." As discussed below, the MAR court’s
decision was not unreasonable and, accordingly, we affirm the
district court’s rejection of this claim.
                       RICHARDSON v. BRANKER                  27
   First, to the extent that Richardson would have used the
police sketches of item 41 to demonstrate that another per-
son’s shoeprints were found at the scene of the crime, that
evidence was already before the jury. As noted previously,
Richardson elicited testimony from Agent Petzka during her
cross-examination that there were shoe prints found on a ceil-
ing tile recovered from the store that did not match the shoes
seized from Richardson. Agent Petzka was questioned about
item 41 as follows:

    Q: When you say that the other footprints found on
    [item] number 41 had a zigzag pattern, what do you
    mean by zigzag pattern?

    A: It’s a pattern where it goes up and then comes
    down and then goes up and then comes back down.

    Q: And that is different than the shoe [Richard-
    son’s shoe] that’s sitting in front of you, isn’t it?

    A:   Yes, it is.

Thus, despite the fact that Richardson did not have a sketch
of item 41 at his disposal, his counsel was able to elicit testi-
mony concerning the type of shoeprints on item 41 and the
fact that those prints were inconsistent with Richardson’s
shoeprint. Accordingly, the sketches of item 41 do not add
any substance to Agent Petzka’s testimony and, therefore, do
not constitute Brady material for this purpose. See McHone v.
Polk, 392 F.3d 691, 701 (4th Cir. 2004) (undisclosed evidence
cannot form basis of a Brady violation if it is consistent with
trial testimony or merely cumulative to undisputed facts).

   Second, with regard to Richardson’s contention that the
sketches of item 41 would have demonstrated that the other
individual’s shoeprints were those of Hedgepeth, this argu-
ment is pure conjecture. Richardson cannot point to substan-
tial evidence that the print on item 41 matches Hedgepeth’s
28                   RICHARDSON v. BRANKER
shoes. The mere fact that the sketches of item 41 and Hedge-
peth’s shoes both displayed a "zigzag" pattern is insufficient,
given the undisputed testimony that the shoe impression on
item 41 contained inadequate detail to make a comparison to
any particular shoe. On this point, Agent Petzka testified as
follows:

     Q. Ms. Petzka, the item number 41 is a large piece
     of sheetrock, isn’t it?

     A.     Yes.

     Q. And when you noted—when you saw it, you
     saw several portions of questioned footwear impres-
     sions, didn’t you?

     A.     Yes.

     Q.     You could see them with the naked eye?

     A. You could see them very faintly if you look at
     it with side lighting, but they were very small por-
     tions and not sufficient for comparison.

          ...

     Q. When you say that there were small portions of
     foot impression on number 41, what exactly do you
     mean?

     A. They were just very small. You could see some
     detail of a shoe impression but it was very faint and
     was only visible by looking at it from the side. We
     could not photograph it, we could not get any record
     of it, to work with, and I was—

     []
                       RICHARDSON v. BRANKER                            29
       A. And I was not able to get anything for compari-
       son purposes.

       Q. Would you have been able to perform any tests
       or are there any type of tests that you could do to
       bring something that’s real faint out? Is there any-
       thing that could do that?

       A. No, there really isn’t. I had a photographer
       come over from the photo lab in an attempt to try
       and use side lighting and everything else, and when
       looked at from directly in front, which is how it has
       to be photographed, they just disappeared.

       Q. Were you able to come up with any idea as to
       the size.

       A.   No.

       Q. Were you able to come up with any minute
       detail whatsoever anywhere as to any shoe?

       A.   Not that I could use for comparison, no.

       Q. Were you able to come up—when you say use
       for comparison, do you mean use for comparison on
       the shoes that you had?

       A. They were insufficient for comparison to any
       shoes.

(Emphasis added.)

  We further observe that Richardson cannot identify any
evidence in the record refuting Agent Petzka’s conclusions.20
  20
    During his post-conviction proceedings, Richardson consulted an
expert in the field of forensic science, who reviewed Agent Petzka’s testi-
30                     RICHARDSON v. BRANKER
Accordingly, we disagree with Richardson’s argument that a
reasonable jury could conclude from the evidence that the pat-
tern in Agent Petzka’s sketches of item 41 matched the pat-
tern on Hedgepeth’s shoes.

                                   ii.

   We next consider certain out-of-court statements made by
Sadie Atkinson, a trial witness, which Richardson asserts
were withheld from him in violation of Brady. In the MAR
court, Richardson attached an affidavit from Atkinson stating,
in part, as follows:

        5. Three times on October 6, 1993, Tim Rich-
        ardson, Kevin Hedgepeth and Michael Newson
        [sic] came to my residence. Upon every visit, Mr.
        Richardson came to the door while the other two
        sat in the small red car. I saw their faces and
        noticed what they were wearing. Their third visit
        was around 11:00 p.m. Tim Richardson came to
        the door and the other two stayed in the car. I
        couldn’t see their faces clearly, but I saw the same
        clothes that they were wearing earlier that day.

     ...

     7. Before the trial, I told district attorney, Keith
     Werner, that Kevin Hedgepeth and Michael Newson
     [sic] were in Tim Richardson’s car when Mr. Rich-
     ardson visited my house on that night. Mr. Werner
     told me that he did not want to hear that right now.
     Mr. Werner told me only to answer the questions
     asked at the trial and not to volunteer information.

mony concerning the insufficiency of the shoeprint impression on item 41.
Based on the information available to her, Richardson’s consultant did not
disagree with Agent Petzka’s conclusion that the shoeprint found on item
41 was insufficient to permit a comparison with another shoeprint.
                        RICHARDSON v. BRANKER                            31
       8. I never told the defense attorneys this informa-
       tion at the trial because they didn’t ask me and I
       didn’t volunteer information because of what Mr.
       Werner told me.21

   Richardson asserts that the above out-of-court statements
made by Atkinson would have provided corroboration for
Richardson’s defense that Hedgepeth was involved in the
crime. However, an obvious weakness in Atkinson’s post-
conviction affidavit is that it contains information contradict-
ing certain aspects of her trial testimony. For instance, in the
affidavit, Atkinson states that Richardson came to her house
on the night of the crime with Hedgepeth. In contrast, at trial,
Atkinson testified that Richardson came to her house on the
night of the crime looking for Hedgepeth:

       Q: Ms. Atkinson, tell the ladies and gentlemen of
       the jury if you saw Mr. Richardson on the 6th of
       October, 1993.

       A:    Yes, I did.

       Q:    Where did you see him?

       A: He came to my front door of my house at the
       trailer where I live now.

       ...

       A: He was at my front door . . . and he asked me
       about two of his friends and I told him I hadn’t seen
       them, and he left. That was all. That was it.

       Q:    What two friends did he ask you about?
  21
    Mr. Werner filed an affidavit in the district court disputing Atkinson’s
account of their discussion. In light of our analysis, it is unnecessary to
resolve any credibility dispute between these two individuals.
32                   RICHARDSON v. BRANKER
     A: He asked for Mike and he asked me for [Kevin]
     Hedgepeth. He didn’t say Mike who; he just said
     Mike and [Kevin] Hedgepeth. That’s all he said.

     Q:    And were they at your residence?

     A:    No, they wasn’t [sic].

     Q:    Were they with [Richardson]?

     A:    I don’t have any idea.

   Atkinson’s trial testimony was consistent with her SBI
interview, in which she stated that Richardson "was alone
when he came to her house." There is no manner in which we
can reconcile Atkinson’s post-conviction affidavit statements
that she saw Richardson together with Hedgepeth on the night
of the crime, with her repeated statements to the contrary that
she had not seen Hedgepeth with Richardson and that Rich-
ardson had asked her whether she had seen Hedgepeth.

  Additionally, Atkinson’s statement in the affidavit that she
"never told the defense attorneys this information at trial
because they didn’t ask me" is refuted by the trial transcript.
Richardson’s counsel probed Atkinson’s recollection on cross
examination, asking her whether Richardson was with Hedge-
peth on the night of the crime:

     A: I told [SBI agents] that I thought [Hedgepeth]
     was with [Richardson] that night; I didn’t know. But
     then he had asked me about [Hedgepeth], so I wasn’t
     sure, you know.

     ...

     Q: When Timothy came to your house, it was
     10:30 or 11:00 o’clock?
                        RICHARDSON v. BRANKER                            33
       A:    Yeah, somewhere in that vicinity, yes.

       Q: And he was looking to get up with [Kevin]
       Hedgepeth?

       A:    With his friends.

       Q: With his friends. And one of those, was that this
       [Kevin] Hedgepeth?

       A:    He did call the name.

       ...

       Q: Did you tell the SBI agents that came to your
       house that you had seen [Hedgepeth] that day?

       A:    I’m not sure.

       Q:    You’re not sure now?

       A:    Not sure of that, no.

(Emphasis added.)

   In light of the conflict between the statements in Atkinson’s
affidavit and her testimony at trial, the impact of her affidavit
statement that she saw Richardson with Hedgepeth on the
night of the crime is significantly lessened. Further, the proba-
tive value of the affidavit statements was minimal because, at
best, those statements placed Hedgepeth at Atkinson’s house
with Richardson nearly forty minutes before the crime could
have occurred.22 Thus, the affidavit statements do not bear on
the testimony of the numerous witnesses whose trial testi-
  22
    According to computer records linked to the store’s alarm system, Ms.
Rich closed the store about 11:41 p.m. Atkinson stated in her affidavit that
Richardson and Hedgepeth arrived at her home around 11:00 p.m.
34                    RICHARDSON v. BRANKER
mony placed Hedgepeth at locations other than the store dur-
ing the time period in which the crimes occurred.23

                                 iii.

   With the above considerations in mind, we conclude our
Brady inquiry by addressing whether the withheld evidence at
issue, when considered cumulatively, is "material" under
Brady. We again pose the question that federal courts must
answer when examining a Brady claim through the lens of
AEDPA: Was the MAR court’s holding that "there is no rea-
sonable possibility that, had the alleged error in question not
been committed, a different result would have been reached
at trial," incorrect to a degree that this conclusion "was so
lacking in justification that [it] was an error well understood
and comprehended in existing law beyond any possibility for
fairminded disagreement?" See Harrington, 131 S. Ct. at 786-
87.

   The answer to this question is "no." The additional evi-
dence concerning the sketches of item 41 did not add any new
facts to the trial evidence, and Richardson’s argument to the
contrary is not supported by the record. In addition, the state-
ments contained in Atkinson’s affidavit were in direct conflict
with the sworn statements she made at Richardson’s trial and,
even if true, serve only to place Richardson and Hedgepeth
together at least 40 minutes before the criminal activity com-
menced. Thus, this evidence, even viewed cumulatively, does
not place Richardson’s trial in such a different light that confi-
dence in the verdict is undermined. See Strickler, 527 U.S. at
290; Kyles, 514 U.S. at 435. At the very least, the MAR
  23
    As stated by the district court, these witnesses include "Anthony
Hedgepeth, Sam Jones, Tug Lynch, and [Hedgepeth’s] uncle and grand-
mother who all place Kevin [Hedgepeth] with his cousin Anthony around
the Tree [an area in town where people were known to hangout], riding
home, or at home during the period when the crimes occurred." 769 F.
Supp. 2d at 915.
                    RICHARDSON v. BRANKER                     35
court’s conclusion in this respect is not "unreasonable" under
the AEDPA standard that we apply. Accordingly, we hold
that Richardson’s Brady claim is without merit, and we affirm
the district court’s award of summary judgment to the State
on this claim.

                               C.

   Finally, we address Richardson’s Atkins claim that he is
mentally retarded, and that his sentence of death therefore
violates the Eighth Amendment’s prohibition against cruel
and unusual punishments. The MAR court rejected this claim
on its merits, and the district court declined to grant this part
of Richardson’s habeas petition. 769 F. Supp. 2d at 927-28.
We review the district court’s decision de novo, and we ana-
lyze the MAR court’s holding in the deferential light man-
dated by AEDPA. Cummings v. Polk, 475 F.3d 230, 237 (4th
Cir. 2007).

   In Atkins, the Supreme Court held that the death penalty
may not be imposed on mentally retarded individuals because
a national consensus had developed against executing such
offenders. 536 U.S. at 316. However, the Supreme Court
observed that "[n]ot all people who claim to be mentally
retarded will be so impaired as to fall within the range of
mentally retarded offenders about whom there is a national
consensus." Id. at 317. Thus, the Supreme Court "left to the
states the task of developing appropriate procedures to deter-
mine whether an inmate who claims to be mentally retarded
is in fact mentally retarded." Walton v. Johnson, 440 F.3d
160, 176 (4th Cir. 2006) (en banc) (citing Atkins, 536 U.S. at
317).

   The method of establishing mental retardation in North
Carolina is provided by statute. Under N.C. Gen. Stat. § 15A-
2005(a) (the statute), the defendant has the burden of proving
that he is mentally retarded by establishing "[s]ignificantly
subaverage general intellectual functioning, existing concur-
36                  RICHARDSON v. BRANKER
rently with significant limitations in adaptive functioning,
both of which were manifested before the age of 18."
N.C.G.S. § 15A-2005(a)(1)(a) (emphasis added).

   The first of these two requirements, "[s]ignificantly subav-
erage general intellectual functioning," is defined by the stat-
ute as "[a]n intelligence quotient [IQ] of 70 or below."
N.C.G.S. § 15A-2005(a)(1)(c). The statute further provides
that the requisite "I.Q." score must derive from "an individu-
ally administered, scientifically recognized standardized intel-
ligence quotient test administered by a licensed psychiatrist or
psychologist." N.C.G.S. § 15A-2005(a)(2).

   The statute also requires that a defendant who claims that
he is mentally retarded establish "significant limitations in
adaptive functioning." N.C.G.S. § 15A-2005(a)(1)(b). This
requirement is defined under the statute as "[s]ignificant limi-
tations in two or more of the following adaptive skill areas:
communication, self-care, home living, social skills, commu-
nity use, self-direction, health and safety, functional academ-
ics, leisure skills and work skills." Id. A defendant claiming
that he is mentally retarded must establish both the "signifi-
cantly subaverage general intellectual functioning" prong and
the "significant limitations in adaptive functioning" prong.
N.C.G.S. § 15A-2005(a)(1).

  The MAR court held an evidentiary hearing to determine
whether Richardson could satisfy his burden of proving that
he is mentally retarded. The MAR court found that Richard-
son failed to establish either of the two requirements set forth
by the statute.

  With respect to the "intellectual functioning" prong, the
MAR court discussed four I.Q. tests that the parties argued
had bearing on the issue whether Richardson had an "[I.Q.] of
70 or below," as required by N.C. Gen. Stat. § 15A-
2005(a)(1)(c). Richardson proffered I.Q. test scores of 64 and
                       RICHARDSON v. BRANKER                          37
67, but, as described below, the MAR court held that these
results were not qualifying I.Q. scores under the statute.

   Richardson’s test score of 64 resulted from an aptitude test
Richardson took in 1991 while enrolled in the tenth grade.
The MAR court noted that a flood destroyed "most of the
information" relating to this test. Accordingly, the MAR court
observed that "[t]here is no raw test data to support this score
as required by the General Statutes, and no way of knowing
who administered or how this test was administered." Thus,
Richardson’s score of 64 on this test was not a qualifying test
score under the statute, because there was no evidence that the
test was individually administered, or was a "scientifically
recognized standardized" I.Q. test, or was "administered by a
licensed psychiatrist or psychologist," each of which is
required under N.C. Gen. Stat. § 15A-2005(a)(2).

   Richardson’s test score of 67 resulted from a Wechsler
Adult Intelligence Scale Third Edition (WAIS III) test that
Richardson took in 2002 at the direction of Dr. John Warren,
a licensed psychologist. As noted by the MAR court, Dr.
Warren did not personally administer this test. Instead, he "di-
rected his Psychometrician, [John] Tatum, to personally
administer this test."24 Dr. Warren was not present when the
test was administered, and Mr. Tatum is not a licensed psychi-
atrist or psychologist. Accordingly, the MAR court held that
Richardson’s test score of 67 was not a qualifying score under
the statute because the test was not "administered by a
licensed psychiatrist or psychologist," as required by N.C.
Gen. Stat. § 15A-2005(a)(2).

  The State proffered test results showing that Richardson
had I.Q. scores of 73 and 74. Richardson’s I.Q. score of 73
  24
   As the district court observed, a "psychometrician" is "a professional
who administers and scores psychological and neuropsychological tests
under the supervision of a licensed psychologist or neuropsychologist."
769 F. Supp. 2d at 8125 n.12.
38                     RICHARDSON v. BRANKER
resulted from a Wechsler Adult Intelligence Scale Revised
(WAIS R) test administered by Dr. John Gorman, a licensed
psychologist, in 1995. Richardson’s I.Q. score of 74 resulted
from a WAIS III test administered by Dr. Mark Hazelrigg, a
licensed psychologist, in 2004. The MAR court found that
these test scores complied with the requirements of N.C. Gen.
Stat. § 15A-2005(a)(2).

   The MAR court concluded that because the only standard-
ized I.Q. tests administered to Richardson meeting the
requirements of the statute resulted in I.Q. scores of 73 and
74, Richardson could not satisfy his burden of proving "sig-
nificantly subaverage general intellectual functioning," i.e.,
"[a]n [I.Q.] of 70 or below." N.C.G.S. § 15A-2005(a)(1)(c).

   We again examine this holding through the deferential stan-
dard of review mandated by AEDPA, as discussed previously.
Because the MAR court’s conclusion that Richardson is not
mentally retarded is a question of fact, we apply the second
prong of the AEDPA standard. Accordingly, we ask whether
the MAR court’s decision "was based on an unreasonable
determination of the facts in light of the evidence presented
in the State court proceeding?" 28 U.S.C. § 2254(d)(2);
accord Miller–El v. Cockrell, 537 U.S. 322, 340 (2003). After
reviewing the record and the parties’ arguments, we find no
error in the MAR court’s determination that Richardson failed
to meet the first prong of the statutory definition of mental
retardation because he does not have a qualifying I.Q. score
of 70 or below.25 Thus, our answer to the question posed
above is "no."
  25
     Richardson contends that the MAR court did not adjudicate the merits
of the issue whether he proved significantly subaverage intellectual func-
tioning. However, Richardson’s contention is refuted by a plain reading of
the transcript of the MAR court’s evidentiary hearing, as well as the MAR
court’s order denying his mental retardation claim. Accordingly, we
decline Richardson’s invitation to review the MAR court’s decision de
novo rather than under the deferential standard of review set forth by
AEDPA.
                     RICHARDSON v. BRANKER                     39
   We are not persuaded by Richardson’s additional argument
that the MAR court should have adjusted downward his I.Q.
scores of 73 and 74 due to the "Flynn effect" and the "practice
effect." As described by Dr. Warren during his testimony, the
"Flynn effect" is the proposition that an individual gains intel-
ligence over time and, thus, an I.Q. test taken later in life will
result in a higher score than had the individual taken the same
I.Q. test at an earlier age. 769 F. Supp. 2d at 925. Dr. Warren
described the "practice effect" as the proposition that an indi-
vidual achieves a higher I.Q. score in subsequent I.Q. tests as
compared to that individual’s initial I.Q. test, when the two
tests are taken in a relatively close time frame. Id. Although
Dr. Warren discussed during the MAR court’s evidentiary
hearing the impact that the "Flynn effect" and the "practice
effect" may have had on Richardson’s I.Q. scores above 70,
the MAR court declined to adjust Richardson’s I.Q. scores on
the basis of those theories.

   For several reasons, we decline to disturb the MAR court’s
decision. First, adoption of the "Flynn effect" and the "prac-
tice effect" theories, and the corresponding adjustment of
Richardson’s I.Q. scores, would require us to engage in a de
novo review of the MAR court’s decision. Indeed, doing so
would require us to make our own factual findings. This is
precisely the result that is forbidden under AEDPA, which
requires deference and respect for a state court’s adjudication
of a claim on the merits.

   Second, Richardson does not cite to any North Carolina
law, nor could we find any such law, requiring courts to con-
sider and apply the "Flynn effect" and the "practice effect."
To the contrary, N.C. Gen. Stat. § 15A-2005(a) sets forth an
I.Q. score threshold of 70 or below without mention of these
theories. If the North Carolina legislature had intended that
the state courts take these and other theories into account
when adjudicating mental retardation claims, the legislature
could have so provided in the statute. Thus, under the AEDPA
standard we apply in this case, we agree with the district
40                      RICHARDSON v. BRANKER
court’s observation that "there is no requirement under N.C.
Gen. Stat. § 15A–2005 for a court to adjust a defendant’s I.Q.
scores downward for such factors." 769 F. Supp. 2d at 927;
see also Green v. Johnson, 515 F.3d 290, 300 n.2 (4th Cir.
2008) (applying Virginia law in reviewing habeas petition and
observing that "neither Atkins nor Virginia law appear to
require expressly that [the Flynn effect or the standard error
of measurement] be accounted for in determining mental
retardation status").26
   26
      We observe that in Walker v. True, 399 F.3d 315, 322 (4th Cir. 2005)
(applying Virginia law), we held that the district court was required to
consider on remand the petitioner’s argument that his I.Q. score was influ-
enced by the Flynn effect for purposes of his Atkins claim. This instruc-
tion, however, was a product of the unusual procedural posture of that
case. Walker had exhausted his potential post-conviction remedies in the
Virginia court system before the Supreme Court issued its decision in
Atkins. 399 F.3d at 318. Under the governing Virginia statute, Walker was
prohibited from filing any successive habeas petitions in the state courts
and his "sole remedy shall lie in federal court." 399 F.3d at 318-19 (citing
Va. Code § 8.01-654.2). Thus, Walker’s claim that he was mentally
retarded was never adjudicated on the merits by a state court. The claim
was brought in the first instance to the district court, which reviewed the
claim de novo. Id. The district court’s decision was premised on the Com-
monwealth’s motion to dismiss, and, accordingly, the district court was
obligated to assume all facts alleged in his habeas petition to be true. Id.
at 319; cf. Winston v. Kelly, 592 F.3d 535, 557 (4th Cir. 2010) (requiring
district court to consider Flynn effect on remand in case not arising under
AEDPA standard of review because the Virginia state courts did not
afford Winston an evidentiary hearing and thus "passed on the opportunity
to adjudicate [his] claim on a complete record").
   By contrast, Richardson’s Atkins claim was fully raised in the MAR
court, which held an evidentiary hearing and received evidence concerning
the Flynn effect and the practice effect. The MAR court adjudicated his
claim on the merits, and, accordingly, we apply the significantly deferen-
tial review mandated by AEDPA to Richardson’s claim. Therefore, con-
trary to Richardson’s contention, our holdings in Walker and Winston do
not require us to overrule the MAR court’s determination that Richardson
is not mentally retarded under North Carolina law. See Winston, 592 F.3d
at 558 (observing that the Supreme Court of Virginia "was unconvinced
by Winston’s evidence concerning the Flynn effect and [the standard error
of measurement]" and opining that "a federal court sitting in habeas could
not conclude that such a holding violated [AEDPA]").
                    RICHARDSON v. BRANKER                    41
   Because we hold that the MAR court did not unreasonably
conclude that Richardson failed to establish "significantly
subaverage general intellectual functioning," we need not
address the MAR court’s conclusion concerning Richardson’s
failure to establish the other requirement of the statute, "sig-
nificant limitations in adaptive functioning." N.C.G.S. § 15A-
2005(a)(1)(b). In sum, the MAR court’s denial of Richard-
son’s motion on the basis that he is not mentally retarded was
neither based on an unreasonable determination of the facts
nor is an unreasonable application of the Supreme Court’s
decision in Atkins. Accordingly, we affirm the district court’s
award of summary judgment in favor of the State with respect
to Richardson’s Atkins claim.

                              III.

  In conclusion, we hold that the district court erred in grant-
ing the habeas petition on the ground that Richardson’s attor-
ney on direct appeal rendered ineffective assistance of
counsel. We reverse this portion of the district court’s judg-
ment.

   We also hold that the district court did not err in awarding
summary judgment to the State with respect to Richardson’s
Brady and Atkins claims. We affirm these portions of the dis-
trict court’s judgment. Accordingly, we remand this case to
the district court with directions that Richardson’s federal
habeas petition be dismissed.

                                       AFFIRMED IN PART,
                                       REVERSED IN PART,
                                          AND REMANDED
