OPINION OF THE COURT
AMBRO, Circuit Judge.
Thomas Affinito was convicted in 1988 of murder and kidnapping in New Jersey state court. After exhausting his state court remedies, Affinito petitioned for a writ of habeas corpus in the United States District Court for the District of New Jersey. The District Court denied Affinito’s petition. We granted a certificate of ap-pealability as to whether Affinito received ineffective assistance of counsel at his trial. While we conclude that Affinito’s counsel failed to provide effective assistance, that failure was not sufficiently prejudicial to warrant granting a writ of habeas corpus.
I. Factual and Procedural Background
On February 22, 1985, Affinito, John Cupsie, and Michael Perez were drinking at a bar called Stash’s Tavern in Carteret, New Jersey. What follows was related primarily by Perez, who was an eyewitness to what occurred throughout that evening and the early morning hours of February 23.
The three men were regular patrons at Stash’s Tavern and had met one another there. It appears, though, that they neither were good friends nor had they known each other very long. On the evening in question, they had been at Stash’s for several hours and eventually began talking over a game of pool. They decided to drive to another bar in Carteret called the City Line. Cupsie drove. The three men arrived just before last call and ordered drinks. Almost immediately, Affini-to and Cupsie began arguing for some unknown reason, but the two seemingly reconciled their differences within a few minutes.
Shortly thereafter, Affinito and Perez left Cupsie at the bar and walked outside. Neither Affinito nor Perez wanted to go home, and the suggestion was made that they could drive around in Cupsie’s car. The two checked the car doors, but they [254]*254were locked. Affinito then stated he could give Cupsie a “sleeper hold” (a wrestling term), render him unconscious, and take his keys. Perez expressed uncertainty in the plan, but Affinito insisted he could knock Cupsie out and do so without hurting him. Perez acceded.
The two men soon rejoined Cupsie inside, and he informed them of his desire to go home. All three returned to Cupsie’s car, and he drove to Affinito’s house. Af-finito was sitting in the back seat, as he had on the car ride from Stash’s to City Line. While parked outside his residence, Affinito pulled out a pipe and asked Cupsie if he wanted to smoke marijuana. Cupsie responded in the affirmative. Affinito, however, did not have any marijuana. He pretended to put marijuana in the pipe and told Cupsie to pass the pipe to Perez. At this point, Affinito grabbed Cupsie from behind and pulled him into the back seat of the car. Cupsie began struggling frantically, and the fight spilled out of the car. During the course of the fight, Affinito pinned Cupsie to the ground and repeatedly punched his face and head until he was bloodied and unconscious. Affinito then said he had to kill Cupsie and strangled him with a shirt until he began foaming at the mouth. With Perez’s help, Affinito put Cupsie in the trunk of the car and drove to a nearby junkyard.1
By the time Affinito arrived at the junkyard, however, Cupsie had regained consciousness. When Affinito opened the trunk, Cupsie punched him in the face in an attempt to fight his way out of the trunk. He was unsuccessful. Affinito again strangled Cupsie, this time killing him. After throwing Cupsie’s body on the ground, Affinito drove the car from the junkyard. He and Perez wiped the car of fingerprints and abandoned it. Affinito also threw the shirts used to strangle Cup-sie and clean the car into a sewer catch basin. He returned to his home around 4:30 a.m. on February 23.
After finding Cupsie’s body in the junkyard later that day and conducting a preliminary investigation, the police took Affinito into custody. At police headquarters, Affinito gave two statements. In the first, he admitted leaving the bars with Cupsie, but he claimed that Cupsie dropped him off at home around 4:00 a.m. In his second statement, Affinito admitted that he killed Cupsie. Affinito alleged, however, that he attacked Cupsie only after Cupsie made homosexual advances toward him.2
Larry Bronson, the counsel retained by Affinito’s family, hired Stanley L. Portnow, M.D., to perform a psychiatric evaluation of Affinito. Portnow’s evaluation of Affini-to’s mental status at the time of the incident was based on two interviews with him, numerous sets of medical and psychiatric records, and police statements given by Affinito and witnesses. Portnow concluded that Affinito suffered from a major psychiatric disorder that “substantially impaired his ability to know or appreciate the nature and quality of his acts or to know that they were wrong.”
In 1987, John P. Russell was substituted as Affinito’s defense counsel.3 Russell [255]*255hired a different psychiatrist, James Fer-retti, M.D.4 Ferretti based his evaluation on a single, fifty-five minute interview with Affinito. During this interview, Ferretti relied on Affinito to provide the facts of the crime. To underscore his reliance, Ferretti provided a disclaimer in his report that the “opinions and diagnosis recommendations and commentary contained in this report are based on the assumption that the patient has been reasonably accurate and truthful in his narration. If this was not the case, my opinions and diagnosis conceivably could be altered.” While Ferretti later reviewed Affinito’s medical and psychiatric records, Russell never provided Ferretti with Affinito’s post-arrest statements to the police.
Affinito was ultimately charged with: (1) purposeful or knowing murder, N.J. Stat. Ann. § 2C:ll-3(a)(l) and (2); (2) first-degree kidnapping, N.J. Stat. Ann. § 2C:13-1(b)(1) and(2); and (3) felony murder, N.J. Stat. Ann. § 2C:ll-3(a)(3). He stood trial in the New Jersey Superior Court in September 1988.
At trial, Russell used Ferretti’s testimony to present diminished capacity and intoxication defenses. Ferretti opined during direct examination that Affinito: (1) was intoxicated the night of the murder; (2) had a personality disorder of the “epi-leptoid variety” which caused him to have “difficulty with impulse control”; and (3) had suffered permanent brain tissue injury brought about by epilepsy and past alcohol abuse, making him more susceptible to the effects of intoxicants. Ferretti concluded that such a “vulnerable brain” — coupled with intoxication, the described personality disorder and stress from a fight — would result in a person lacking the capacity to “knowingly and by design perpetrate a murder.”
On cross-examination, Ferretti testified that his opinion might change if the facts were materially different from those provided by Affinito. The prosecution then questioned Ferretti regarding Affinito’s altercation and strangling of Cupsie in the junkyard. (Ferretti was not even aware of these facts because Affinito omitted mention of them during their interview, and Russell had failed both to mention them to Ferretti and provide him with Affinito’s statements to the police.) Ferretti responded that he “would not apply diminished capacity at that point because I would think [Affinito] formulated intent.” Ferretti reiterated this position on redirect, though with the qualifying assumption that the additional facts were true.
In its case in rebuttal, the State called Dr. Irwin N. Perr as a psychological expert. After reviewing medical records and interviewing Affinito for approximately three hours, Perr concluded that Affinito was not an epileptic per se and did not suffer from any type of brain damage or cognitive disorder.
[256]*256A jury convicted Affinito on all counts. The purposeful or knowing murder conviction was merged with the felony murder conviction, for which Affinito received a sentence of life imprisonment with parole ineligibility lasting thirty years. (He received a consecutive sentence of twenty-five years for the first degree kidnapping conviction.)
In 1989 Affinito appealed his convictions and sentences. In his brief to the Appellate Division of the New Jersey Superior Court, Affinito alleged the trial court committed several errors, including an improper jury charge regarding diminished capacity (erroneously placing on Affinito the burden of proving lack of intent in establishing diminished capacity). In February 1991 the Appellate Division affirmed Affin-ito’s convictions and sentences. Later that year, the Supreme Court of New Jersey denied Affinito’s petition for certification.
Nearly three years later Affinito filed in the Superior Court a petition for post-conviction relief under New Jersey’s Post-Conviction Relief Act (“PCRA”), N.J. Stat. Ann § 2A:67-16. In the petition he alleged his trial counsel was ineffective by not presenting a viable diminished capacity defense. Specifically, Affinito argued Russell failed to prepare Ferretti properly. At the PCRA hearing, Affinito offered the testimony of a criminal lawyer as an expert. That expert opined that Russell was ineffective because he failed to provide, inter alia, Ferretti with a copy of Affini-to’s statements to the police, did not require Ferretti to consult with Portnow and called Ferretti as an expert instead of the (presumably) more prepared Portnow.
In early 1996 the Superior Court denied Affinito’s request for relief, concluding that he failed to sustain his burden of proving ineffective assistance of counsel. Significantly, the Court found Russell’s choice of Ferretti was strategic and that Affinito failed to prove whether Portnow was available at the time of the trial and prepared to testify. The Court also found that Af-finito failed to demonstrate Portnow’s testimony would have differed from Ferretti’s had Portnow been called as Affinito’s expert.
Affinito appealed once more to the Appellate Division of the Superior Court, which affirmed for the same reasons. Later that year, the New Jersey Supreme Court, as it had done in the direct appeal of Affinito’s convictions, denied his request for certification.
Affinito then filed a petition seeking a writ of habeas corpus in the United States District Court for the District of New Jersey. He argued that his Sixth Amendment right to effective assistance of counsel was violated for the same reasons he asserted in the New Jersey courts. As noted, the District Court denied Affinito’s petition, and we granted a certificate of appealability on the issue of whether Russell provided ineffective assistance of counsel.5
II. Standard of Review
We exercise plenary review over the District Court’s decision denying Affinito’s habeas petition. Stevens v. Del. Corr. Ctr., 295 F.3d 361, 368 (3d Cir.2002). Overlaying our review standard, however, is the Antiterrorism and Effective Death Penalty Act of 1996 (“AEDPA”). For matters of fact, a federal court reviewing a habeas petition must “presume that the ... findings of both state trial and appellate courts are correct, a presumption that can only be overcome on the basis of clear and convincing evidence to the contrary.” Id. (citing 28 U.S.C. § 2254(e)(1)); see also [257]*257Williams v. Taylor, 529 U.S. 362, 402-13, 120 S.Ct. 1495, 146 L.Ed.2d 389 (2000).
As for legal conclusions, Williams instructs that a federal court may only grant habeas relief if the state adjudication “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.” Williams, 529 U.S. at 402-03, 120 S.Ct. 1495 (quoting 28 U.S.C. § 2254(d)(2)); see also Werts v. Vaughn, 228 F.3d 178, 196 (3d Cir.2000). Under AEDPA, “we must first identify the applicable Supreme Court precedent and determine whether it resolves the petitioner’s claim.” Werts, 228 F.3d at 197 (citing Matteo v. Superintendent, SCI Albion, 171 F.3d 877, 888 (3d Cir.1999)). A decision is “contrary to” clearly established federal law “if the state court arrives at a conclusion opposite to that reached by [the Supreme] Court on a question of law or if the state court decides a case differently than [the Supreme] Court has on a set of materially indistinguishable facts.” Williams, 529 U.S. at 413, 120 S.Ct. 1495; see also Werts, 228 F.3d at 196. Further, “it is not sufficient for the petitioner to show merely that his interpretation of Supreme Court precedent is more plausible than the state court’s; rather, the petitioner must demonstrate that Supreme Court precedent requires the contrary outcome.” Werts, 228 F.3d at 197 (quoting Matteo, 171 F.3d at 888).
“If we determine that the state court decision is not ‘contrary to’ the applicable Supreme Court precedent, then we are required to advance to the second step in the analysis - whether the state court decision was based on an ‘unreasonable application of Supreme Court precedent.” Id. (citing Matteo, 171 F.3d at 888). Here, “a federal habeas court [may] grant the writ if the state court identifies the correct governing legal principle from [the Supreme] Court’s decision but unreasonably applies that principle to the facts of the prisoner’s case.” Williams, 529 U.S. at 413, 120 S.Ct. 1495. In this inquiry, “we are not authorized to grant habeas corpus relief simply because we disagree with the state court’s decision or because we would have reached a different result if left to our own devices.” Werts, 228 F.3d at 197 (citing Matteo, 171 F.3d at 889); see also Williams, 529 U.S. at 411, 120 S.Ct. 1495. Rather, the state court’s application of Supreme Court precedent must have been “objectively unreasonable.” Werts, 228 F.3d at 197 (citations omitted). In other words, a “federal habeas court should not grant the petition unless the state court decision, evaluated objectively and on the merits, resulted in an outcome that cannot reasonably be justified under existing Supreme Court precedent.” Id.
III. Affinito’s Ineffective Assistance of Counsel Claim
Affinito alleges a violation of his Sixth Amendment right to effective assistance of counsel. Although a number of issues are raised, Affinito essentially argues that Russell provided ineffective assistance because he decided to use Ferretti as the defense expert witness rather than Port-now and failed to provide Ferretti with all relevant discovery documents. We conclude that Russell’s performance was deficient. Nonetheless, this does not require a contrary outcome, even in the face of an erroneous jury instruction relating to diminished capacity.
A. Ineffective Assistance of Counsel Standard
The Sixth Amendment right to effective assistance of counsel is not intended “to improve the quality of legal representation, although that is a goal of considerable [258]*258importance to the legal system. The purpose is simply to ensure that criminal defendants receive a fair trial.” Strickland v. Washington, 466 U.S. 668, 689, 104 S.Ct. 2052, 80 L.Ed.2d 674 (1984). In Strickland, the Supreme Court established a two-prong test to determine when a defense counsel’s representation was so inadequate as to warrant reversal of a conviction.
A defendant first must establish his counsel’s representation was constitutionally deficient. Id. at 687, 104 S.Ct. 2052. This standard is met if counsel’s performance “fell below an objective standard of reasonableness.” Id. at 688, 104 S.Ct. 2052. Judicial scrutiny in this regard, however, is highly deferential. Id. at 689, 104 S.Ct. 2052.
It is all too tempting for a defendant to second-guess counsel’s assistance after conviction or adverse sentence, and it is all too easy for a court, examining counsel’s defense after it has proved unsuccessful, to conclude that a particular act or omission of counsel was unreasonable. A fair assessment of attorney performance requires that every effort be made to eliminate the distorting effects of hindsight, to reconstruct the circumstances of counsel’s challenged conduct, and to evaluate the conduct from counsel’s perspective at the time.
Id. (internal citation omitted). Therefore, a court “must indulge a strong presumption that counsel’s conduct falls within the wide range of reasonable professional assistance.” Id.
The second Strickland prong is reached only when the first exists. If so, a defendant must demonstrate a “reasonable probability that, but for counsel’s unprofessional errors, the result of the proceeding would have been different.” Id. at 694, 104 S.Ct. 2052. In adopting this standard, the Strickland Court determined that a defendant must show more than “that the errors had some conceivable effect on the outcome of the proceeding.” Id. at 693, 104 S.Ct. 2052. While a defendant need not show the error “more likely than not altered the outcome in the case,” id. at 693, 104 S.Ct. 2052, it nonetheless must be “sufficient to undermine confidence in the outcome.” Id. at 694, 104 S.Ct. 2052.
B. Application of the Strickland Standard
Affinito argues the District Court erred in concluding that the New Jersey Courts reasonably applied Strickland. As stated previously, each individual argument derives from Russell’s decision to use Fer-retti as an expert witness and failure to provide him with all relevant discovery documents. First, Affinito alleges Ferret-ti was not qualified to testify in support of a diminished capacity defense and that Portnow’s prior evaluation should not have been ignored. Affinito also claims it was unreasonable to have Ferretti testify when he had spent only fifty-five minutes interviewing Affinito, reviewed “no documents,” including Affinito’s “medical and mental health history,” and supported his testimony with the unknown diagnosis of “vulnerable brain.” Finally, Affinito contends that Russell’s failure to provide Ferretti with Affinito’s statements to police fell below any objective standard of reasonableness.
1) Was the Performance of Affinito’s Counsel Constitutionally Deficient?
At the outset, we are unpersuaded that Ferretti was inherently unqualified as an expert witness or that hiring him was unreasonable. Strickland provides that counsel has wide latitude in making strategic and tactical decisions. 466 U.S. at 669, 104 S.Ct. 2052. Determining which psychiatric expert to consult is such a deci[259]*259sion, be it strategic or tactical.6 See United States v. Kirsh, 54 F.3d 1062, 1072 (2d Cir.1995).
In order to circumvent the teachings of Strickland, Affinito attempts to paint Fer-retti as incompetent by isolating a single statement from his direct testimony. Answering a question on Affinito’s mental capacity, Ferretti stated that Affinito “was not acting with mature decision-making capacity and good judgment, [and] therefore had diminished capacity.” Affinito claims this demonstrates Ferretti lacked an understanding of the legal definition of diminished capacity - a mental disease or defect that negates the relevant state of mind required for an offense (here intent). See N.J. Stat. Ann. § 2C:4-2; State v. Galloway, 133 N.J. 631, 628 A.2d 735, 743 (1993).
But in answering the very next question, Ferretti stated that - in light of Affinito’s medical history, his intoxication at the time of the crime and the stress of a fight - Affinito lacked the capacity “to knowingly and by design perpetrate a murder.” This demonstrates Ferretti did understand the diminished capacity defense. In fact, Fer-retti’s uncontroverted testimony establishes him as an expert qualified in the field of psychiatry who has testified in “several hundred” court cases. In this context, retaining him was reasonable.
In addition, Ferretti’s examination of Affinito was sufficient based on the record before us. One complaint of Affinito’s is that Ferretti interviewed him for only fifty-five minutes. While Ferretti may have interviewed Affinito for a shorter period of time than either Portnow or the State’s psychiatric expert, Affinito does not state why, or even if, a fifty-five minute interview is insufficient or contrary to professional standards. And as just stated, Ferretti’s uncontroverted testimony establishes him as a psychiatric expert. While a short interview suggests the possibility of a less than thorough evaluation and an unprepared expert witness, Affinito fails to make a persuasive case that, even at this low threshold, his counsel was ineffective.
As for whether Ferretti reviewed any medical or personal documents, Affinito’s claim of no review is incorrect. Ferretti admitted that he had no written background information at the time of his examination. He testified, however, that he reviewed “background material later on, and that involves virtually every aspect of [Affinito’s] life, medical history, work history, legal history and family history.” This background material, Ferretti opined, supported his independent conclusions.
Further, selecting Ferretti to testify was a reasonable tactical decision because his and Portnow’s evaluations, while not identical, are similar. Both noted Affinito had seizures in the past and a personality disorder that lowered his impulse control. Both stated Affinito was an alcoholic and long-time abuser of various drugs. Both based their conclusions on the fact that, on the night of the murder, Affinito was suffering from a convulsive disorder, was highly intoxicated and was attempting to thwart a perceived homosexual advance from Cupsie. In addition, Ferretti’s use of the phrase “vulnerable brain” is not that dissimilar from Portnow’s report describ[260]*260ing Affinito as a “congenitally damaged individual” and a “central nervous system damaged individual.” One could take issue with Ferretti’s choice of words, but this does not demonstrate that Russell’s reliance on Ferretti’s expert opinion was unreasonable.
We conclude, however, that Russell’s failure to provide Ferretti with Affinito’s statements to the police fell below any constitutionally required standard of reasonable representation. Affinito’s statement to the police differed in several respects from the version of the incident told to Ferretti. Specifically, Affinito failed to mention the second strangling at the junkyard. On cross-examination, Ferretti was asked a series of hypothetical questions to determine if his diagnosis of diminished capacity would change, including the following:
[I]f Affinito further threw [the victim] in the trunk, drove him several blocks away from that location in a deserted area, opened the trunk and [the victim] was still alive and tried to get out of the trunk and Affinito beat him and strangled him and killed him at that spot, how about those factors?
Unbeknownst to Ferretti, this hypothetical mirrored the actual facts of the case. Fer-retti replied that, under those facts, he “would not apply diminished capacity at that point because I would think he formulated intent.”
When the key issue in a criminal case is whether the defendant suffered from diminished capacity, we can think of nothing more critical than ensuring that the defense’s psychiatric expert has as complete and accurate a description of the facts and circumstances surrounding the crime as possible. The decision not to avail Ferret-ti of Affinito’s statements defies logic. A defendant’s own statements to the police have to be some of the most, if at times not the most, crucial documents with which an evaluating mental health expert should be familiar. It is almost inconceivable that Ferretti could take the witness stand without knowing Affinito engaged in a second struggle with Cupsie at the junkyard and strangled him again. This was not a trial tactic, it was gross incompetence. Even assuming the decision not to provide Fer-retti these statements was deliberate, it satisfies the first prong of Strickland. See United States v. Tucker, 716 F.2d 576, 586 (9th Cir.1983) (stating that some “defense strategies may be so ill-chosen that they may render counsel’s overall representation constitutionally deficient”).7 Any intimation to the contrary by the New Jersey Courts is an unreasonable application of Strickland.
2) Did Affinito Suffer Prejudice Because of His Counsel’s Error?
Having concluded that Russell’s failure to provide Affinito’s statements to Ferretti was constitutionally deficient, we examine whether this error satisfies the second, or prejudice, prong of Strickland. To constitute prejudice, Russell’s error must undermine our confidence in the outcome of the case. Strickland, 466 U.S. at 694, 104 S.Ct. 2052. Admittedly, this error (leading to Ferretti’s reversal of opinion on cross-examination) de facto prevented Affinito from presenting any diminished capacity defense.
In the New Jersey Courts and before us, Affinito points to Portnow’s evaluation, made with full knowledge of the facts of the case, as strong evidence supporting his [261]*261diminished capacity defense and undermining his conviction. In response, the Appellate Division of the Superior Court concluded on PCRA appeal that, had Portnow been called to testify, “his conclusion would have been subject to a similarly damaging cross-examination as was” Fer-retti’s. Therefore, Affinito had not demonstrated “a reasonable likelihood that a different result would have been reached.” Under AEDPA, it is not for us to determine whether we agree with, or would rule identically to, the New Jersey Courts. Our only inquiry is whether their application of Strickland was objectively unreasonable. It was not, even assuming that Portnow would have testified with full knowledge of the facts and would not have abandoned the diminished capacity defense as Ferretti did.8
Portnow’s written report contained many omissions and inconsistencies when compared to Perez’s eyewitness testimony. In Portnow’s report, Affinito is quoted as stating that Perez took out a pipe, put white powder into it, and smoked it. But Perez testified Affinito had pulled out a pipe and pretended to fill it with marijuana. Affinito is also quoted as saying that Cupsie started “to climb out of his seat to get in the back with me.” Once again, Perez testified that Affinito was unprovoked and grabbed Cupsie unaware from behind. Portnow’s report also fails to address any of the specific facts that provide the context for Cupsie’s death - such as Affinito’s expressed desire to take the car, his talk of being able to render Cupsie unconscious with a sleeper hold, lulling Cupsie into a vulnerable position with the ruse of smoking marijuana, the statement (when Cupsie was already bloody and unconscious) that Cupsie had to be killed, the decision to dispose of the body in a junkyard, and the second strangling upon discovering that Cupsie was not, in fact, dead.
Unlike our dissenting colleague, we believe these omissions and inconsistencies terminally undermine Affinito’s defense. First, the inconsistencies noted in the preceding paragraph involve physical actions (who did what), not Affinito’s alleged auditory hallucinations (who said what). (Per Portnow’s report, Affinitio “denies visual hallucinations and paranoid ideation.”) Further, Portnow premised his opinion on Cupsie initiating the altercation, writing in the “Conclusions” section of his report that “Cupsie made a physical advance towards Affinito which sparked off a seizure like rage in Affinito.” But as just discussed, Perez testified that Cupsie made no physical advances in the car and was the victim of an unprovoked attack. Because Affinito admittedly was not suffering from visual hallucinations, the lynchpin of Portnow’s entire analysis is suspect. In addition, Perez’s testimony is internally consistent, painting the story of a joyriding plan gone horribly wrong. Portnow’s report makes little attempt to put the events of the evening in context.
Affinito had the opportunity to call Port-now, or another psychological expert, to testify at the PCRA hearing, but failed to do so (for whatever reason). In this con[262]*262text, we will not speculate on the outcome of theoretical testimony, especially when many of Affinito’s arguments on appeal are based on the supposed thoroughness and quality of Portnow’s evaluation and report.9 Given the overwhelmingly one-sided nature of the evidence in this case and the failure of Portnow’s report to address this evidence adequately, Affinito has failed to meet his demanding burden to demonstrate that the PCRA Court unreasonably applied Strickland.
C. Erroneous Jury Instruction
On direct appeal, the prosecution conceded that Affinito was erroneously required to prove diminished capacity by a preponderance of the evidence, violating his due process right to have the prosecution prove intent beyond a reasonable doubt. See Humanik v. Beyer; 871 F.2d 432, 443 (3d Cir.1989).10 The Superior Court found harmless error, largely based on Ferretti’s admission on cross-examination that the actual facts of the case were inconsistent with diminished capacity. But this only covers one constitutional error (the incorrect instruction) with another (the failure to provide Ferretti with all the facts of the case). Indeed, our dissenting colleague argues that “[h]ad a properly prepared expert testified, Affinito would have obtained a new trial based on the erroneous diminished capacity instructions that infected his first trial.”
This interrelating (some might say compounding) of errors, however, is ultimately harmless.11 “Humanik does not compel or even permit us to grant [a writ of habeas corpus ] without considering whether the error was harmful. A contrary holding would violate well-settled Supreme Court precedent that ‘a constitutional error does not automatically require reversal of a conviction.’ ” Kontakis v. Beyer, 19 F.3d 110, 115 (3d Cir.1994) (quoting Arizona v. Fulminante, 499 U.S. 279, 306, 111 S.Ct. 1246, 113 L.Ed.2d 302 (1991)). An error is harmless unless it “had [a] substantial and injurious effect or influence in determining the jury’s verdict.” Id. (quoting Kotteakos v. United States, 328 U.S. 750, 776, 66 S.Ct. 1239, 90 L.Ed. 1557 (1946)).12 Overwhelming evidence that a defendant acted with intent may also render an erroneous jury instruction harmless. See id. at 118.
Based on the strong evidence in the record, and with scant evidence putting a contrary outcome in play, we conclude that [263]*263the trial court’s erroneous instruction did not have a substantial and injurious effect on the jury’s verdict (even absent Ferretti giving up Affinito’s diminished capacity defense). As detailed in the previous section, the written report of Dr. Portnow contained many, and major, inconsistencies and omissions when compared to Perez’s uncontroverted eyewitness testimony.
Further, the testimony of Dr. Perr, the State’s psychological expert, was comprehensive.13 Based upon extensive testing and evaluation, Dr. Perr concluded that Affinito was of normal intelligence, had issues with impulse control, and had an anti-social personality. Perr concluded, however, that Affinito did not suffer from brain damage of any kind or from any disorder that prevented him from forming the requisite intent to commit knowing or purposeful murder. In addition, Perr noted that Affinito was not an epileptic per se, had suffered only one possible seizure in the seven years prior to the murder, and was not more susceptible to the influence of drugs and/or alcohol as a result of his past seizures. Finally, this conclusion was not in any way based upon the second strangling.14
In this context, the evidence of Affinito’s diminished capacity is so underwhelming and remote that, even with Ferretti’s concession aside and a correct jury instruction in place, we perceive no reasonable likelihood of it prevailing. Thus we disagree with the dissent’s conclusions that Affinito had a “seemingly ironclad” winning argument on direct appeal and that there is a reasonable probability Affinito would have been convicted of a lesser included offense at a new trial.
IV. Conclusion
Despite the two constitutional errors before us, we nonetheless conclude that the evidence of diminished capacity was so threadbare, and the evidence of knowing and purposeful intent to murder so strong, that the jury’s guilty verdict was not undermined. The errors - slipshod as they were and normally requiring a new trial - in the circumstances of this unique case were harmless. Accordingly, we affirm the District Court’s denial of Affinito’s petition for a writ of habeas corpus.