Full opinion text
McHUGH, Circuit Judge. Kendrick Simpson is a state prisoner in Oklahoma. After a bifurcated proceeding, the jury convicted Mr. Simpson of two counts of first-degree murder and sentenced him to death. He now appeals the district court's denial of his petition for federal habeas relief under 28 U.S.C. § 2254. Exercising jurisdiction under 28 U.S.C. §§ 1291 and 2253, we affirm. I. BACKGROUND A. Factual History Pursuant to the Anti-Terrorism and Effective Death Penalty Act (AEDPA), we presume the factual findings of the Oklahoma Court of Criminal Appeals (OCCA) are correct, absent clear and convincing evidence to the contrary. See 28 U.S.C. § 2254(e)(1) ; Schriro v. Landrigan , 550 U.S. 465, 473-74, 127 S.Ct. 1933, 167 L.Ed.2d 836 (2007). We therefore state the facts surrounding the murders as found by the OCCA on direct appeal: On the evening of January 15, 2006, Jonathan Dalton, Latango Robertson and [Mr. Simpson] decided to go to Fritzi's hip hop club in Oklahoma City. Prior to going to the club, the three drove in [Mr.] Dalton's white Monte Carlo to [Mr. Simpson's] house so that [Mr. Simpson] could change clothes. While at his house, [Mr. Simpson] got an assault rifle[,] which he brought with him. Before going to Fritzi's, the men first went to a house party where they consumed alcohol and marijuana. When they left the party, [Mr. Simpson] put the assault rifle into the trunk of the Monte Carlo, which could be accessed through the back seat. The three arrived at Fritzi's between midnight and 1:00 a.m. on January 16. Once inside, they went to the bar to get a drink. [Mr. Simpson] and [Mr.] Dalton also took a drug called "Ecstasy." After getting their drinks, [Mr.] Dalton and [Mr.] Robertson sat down at a table while [Mr. Simpson] walked around. When [Mr. Simpson] walked by London Johnson, Anthony Jones and Glen Palmer, one of the three apparently said something to him about the Chicago Cubs baseball cap that he was wearing. [Mr. Simpson] went back to the table and told [Mr.] Dalton and [Mr.] Robertson that some guy had given him a hard time about his cap. At some point, [Mr. Simpson] approached [Mr.] Johnson, [Mr.] Jones and [Mr.] Palmer again. During this encounter, [Mr. Simpson] told them that he was going to "chop" them up. After making this threat, [Mr. Simpson] walked away. He returned a short time later and walked up to Palmer. [Mr. Simpson] extended his hand and said, "We cool." [Mr.] Palmer hit [Mr. Simpson] in the mouth knocking him to the floor. [Mr. Simpson] told [Mr.] Dalton and [Mr.] Robertson that he wanted to leave and the three of them left the club. Out in the parking lot, [Mr. Simpson], [Mr.] Dalton and [Mr.] Robertson went to [Mr.] Dalton's Monte Carlo. Before leaving, they talked with some girls who had come out of the club and were parked next to them. The girls told the men to follow them to a 7-[Eleven] located at NW 23rd Street and Portland. When they arrived at the store, [Mr. Simpson], [Mr.] Dalton and [Mr.] Robertson backed into a parking space toward the back door and the girls pulled in next to the pumps. While the men were sitting in the Monte Carlo, they saw [Mr.] Johnson, [Mr.] Jones and [Mr.] Palmer drive into the parking lot in [Mr.] Palmer's Chevy Caprice. They recognized [Mr.] Palmer as the person who had hit [Mr. Simpson] at Fritzi's. [Mr.] Dalton told [Mr. Simpson] to "chill out" but [Mr. Simpson] was mad and wanted to retaliate against [Mr.] Palmer. When [Mr.] Palmer drove out of the parking lot onto 23rd Street and merged onto I-44, [Mr. Simpson] told [Mr.] Dalton to follow them. While they were following the Chevy, [Mr. Simpson], who was sitting in the front passenger seat, told [Mr.] Robertson, who was sitting in the back seat, to give him the gun. He told [Mr.] Robertson that if he had to get the gun himself, there was going to be trouble. [Mr.] Robertson reached through the back seat into the trunk and retrieved the gun for [Mr. Simpson]. [Mr.] Dalton followed the Chevy as it exited the interstate onto Pennsylvania Avenue. He pulled the Monte Carlo into the left lane beside the Chevy as they drove on Pennsylvania Avenue and [Mr. Simpson] pointed the gun out his open window and started firing at the Chevy. When the Chevy was hit with bullets, [Mr.] Palmer was driving, [Mr.] Jones was sitting in the front passenger seat and [Mr.] Johnson was in the back seat. [Mr.] Johnson heard about twenty rapid gun shots and got down on the floor of the car. He did not see the shooter but noticed a white vehicle drive up beside them. The Chevy jumped the curb and hit an electric pole and fence before coming to a stop. [Mr.] Palmer and [Mr.] Jones had been shot. [Mr.] Jones had been shot in the side of his head and torso and was unconscious. [Mr.] Palmer had been shot in the chest. He was initially conscious and able to talk but soon lost consciousness when he could no longer breathe. [Mr.] Johnson tried to give both [Mr.] Jones and [Mr.] Palmer CPR but was unsuccessful. He flagged down a car that was driving by and asked the driver to get help. Both [Mr.] Palmer and [Mr.] Jones died at the scene from their gunshot wounds. After he fired at the Chevy, [Mr. Simpson] said, "I'm a monster. I just shot the car up." He added, "They shouldn't play with me like that." [Mr.] Dalton kept driving until they reached a residence in Midwest City where he was staying. They dropped the gun off and switched cars, and then [Mr.] Dalton, [Mr.] Robertson and [Mr. Simpson] went to meet some girls they had talked to at Fritzi's. Simpson v. State (Simpson I ), 230 P.3d 888, 893-94 (Okla. Crim. App. 2010) (footnotes in original). B. Procedural History 1. State Court Proceedings a. Criminal trial and sentencing The State of Oklahoma charged Mr. Simpson with the first-degree murders of Glen Palmer and Anthony Jones and with discharging a firearm with intent to kill London Johnson. Id. at 893. The prosecution sought a penalty of death for each murder. Prior to trial, Dr. Phillip Massad, a clinical psychologist, evaluated Mr. Simpson's mental condition. Mr. Simpson disclosed to Dr. Massad that, when Mr. Simpson was sixteen years old, a friend ambushed and shot him for refusing to kill a government witness scheduled to testify in the friend's criminal trial. Mr. Simpson suffered five gunshot wounds and spent two months hospitalized and comatose. Even after his release from the hospital, Mr. Simpson was readmitted frequently for treatment of complications arising from infections. He endured sixteen surgeries over a seven-month period, and feared his attackers would return to kill him. Dr. Massad concluded Mr. Simpson suffered from Post-Traumatic Stress Disorder (PTSD) as a result of the shooting. Mr. Simpson's counsel notified the court he intended to present evidence of Mr. Simpson's PTSD and to call Dr. Massad as an expert witness on that topic. The defense planned to elicit testimony from Dr. Massad that Mr. Simpson suffered from PTSD and that this condition affected his ability to form the intent of malice aforethought required for a first-degree murder conviction. The State moved to exclude Dr. Massad from testifying at the guilt stage of trial. At a hearing on the matter, defense counsel represented that Dr. Massad would testify it was "possible that the PTSD affected [Mr. Simpson] to the extent that he was not able to form the specific intent" to kill, and that, because of his PTSD, Mr. Simpson would have "magnified in his own mind the threat" the victims presented. Trial Mot. Hr'g Tr. at 18 (Sept. 19, 2007). As the State notes, however, Dr. Massad's psychological report "never indicate[d] that [Mr. Simpson's PTSD] prevent[ed] him from forming an intent to kill" or from "know[ing] what he was doing was wrong." Id. at 11-12. The trial court granted the State's motion, holding that Oklahoma law precludes testimony that a defendant could not have formed the specific intent to commit a crime, except in the context of an intoxication or insanity defense, neither of which had been advanced by Mr. Simpson at that time. The jury rendered its decision finding Mr. Simpson guilty of the first-degree murders of Mr. Palmer and Mr. Jones. In the ensuing penalty stage, the State alleged four aggravating factors it claimed warranted a sentence of death: 1. [Mr. Simpson], prior to the time of sentencing, was convicted of a felony involving the use or threat of violence to [another] person [ ("Prior Violent Felony Aggravator") ]; 2. [Mr. Simpson] knowingly created a great risk of death to more than one person [ ("Risk of Multiple Deaths Aggravator") ]; 3. The murder was especially heinous, atrocious, or cruel [ ("HAC Aggravator") ]; 4. At the present time there exists a probability that [Mr. Simpson] would commit criminal acts of violence that would constitute a continuing threat to society [ ("Continuing Threat Aggravator") ]. Trial R. vol. 1 at 44. Mr. Simpson asserted three factors in mitigation: (1) his age, (2) his mental state (PTSD diagnosis), and (3) his family support. i. Aggravating evidence presented at sentencing The State moved to incorporate all the evidence presented during the guilt stage and-after determining the evidence would be relevant to the HAC Aggravator, the Continuing Threat Aggravator, and the Risk of Multiple Deaths Aggravator-the court granted the motion. In addition, Mr. Simpson stipulated that he had previously received a seven-and-a-half-year prison sentence for armed robbery, and the victim of that crime, Hung Pham, appeared in support of the State's case in aggravation. Mr. Pham testified that Mr. Simpson and two other men forced themselves into Mr. Pham's home at gunpoint. Mr. Pham provided compelling details, stating that Mr. Simpson shoved the gun in Mr. Pham's face, forced him inside, and beat him in the face and back with the gun. After taking Mr. Pham's wallet, Mr. Simpson pulled Mr. Pham into a bathroom closet, forced him to kneel on the floor, and demanded all of his money. When Mr. Pham replied that he did not have any more money, Mr. Simpson shot Mr. Pham in the head and left with Mr. Pham's wallet. Mr. Pham remembers the encounter vividly, "[b]ecause ... [Mr. Simpson] hit my face, everything, he hurt me a lot. I remember forever." Trial Tr. vol. 7 at 96-97. The State also relied on the testimony of Roy Collins, a jailhouse informant who had temporarily shared a cell with Mr. Simpson. Hoping to leverage a deal with the district attorney's office for his own early release, Mr. Collins asked Mr. Simpson about the murders. Mr. Collins testified that Mr. Simpson admitted to the altercation at Fritzi's, seeing the victims at the 7-Eleven, following them, and then firing the assault rifle into their car. Mr. Collins further stated that Mr. Simpson expressed no remorse for the murders and even tried to hire Mr. Collins to kill Mr. Johnson, the surviving victim, and to assault two pregnant women listed as State witnesses. Mr. Collins also testified that Mr. Simpson would smile and laugh when talking about the murders and that Mr. Simpson thought he was a "gangster[ ]" like "Tupac or Biggie Small." Id. at 47. Mr. Collins reported that Mr. Simpson "couldn't believe the victims' families were crying" because, according to Mr. Simpson, the victims "were gangbangers, that's the life they lived, that's the life they chose." Id. at 54-55. Mr. Collins also indicated that he could tell Mr. Simpson was a member of the Bloods gang because "[h]e's got red ink all over his neck." Id. at 58-59. Finally, the prosecution presented victim impact statements from Rosalind Jones, the mother of Anthony Jones, and Tiarra Palmer, the sister of Glen Palmer. ii. Mitigating evidence presented at sentencing The defense called six witnesses in mitigation: Dr. Massad, to testify about Mr. Simpson's PTSD diagnosis; Evan Gatewood, to impeach Mr. Collins; and Mr. Simpson's mother, grandmother, aunt, and ex-girlfriend, to testify about Mr. Simpson's upbringing and family support. The vast majority of the mitigating evidence focused on the ambush and shooting of Mr. Simpson and his long road to recovery. The witnesses indicated that family members visited Mr. Simpson every day in the hospital and that his mother believed "[h]e was on his dying bed." Id. at 153. Dr. Massad testified that Mr. Simpson reported being "paranoid hostile" and hypervigilant as a result of having been shot. Id. at 190-92. Dr. Massad also testified at length about the basis of his diagnosis that Mr. Simpson suffered from PTSD and about the typical symptoms of the disorder. He explained that people suffering from PTSD "might be hypersensitive and overreact" to common situations. Id. at 166. Additionally, such a person could be "hypervigilant," constantly on "alert and watchful for danger," and could experience "exaggerated startle response[s] and other symptoms." Id. at 167. Dr. Massad further opined that drugs or alcohol could exacerbate this hypersensitivity and paranoia because they can "increase the likelihood that [a person] would react or overreact." Id. Mr. Simpson's aunt highlighted examples of this paranoia and hypersensitivity in her testimony, noting Mr. Simpson was constantly terrified the men who had shot him would return and finish the job. He was "paranoid and scared" to the point he refused to open the door when people came to visit, and he moved out of his mother's house because it was too close to the site of the shooting. Id. at 205-06. Most of the testimony from Mr. Simpson's family focused on the family's love and support of Mr. Simpson. They gave limited detail about his childhood, characterizing him as a good child with a relatively normal upbringing. There was also testimony that Mr. Simpson's grandmother was primarily responsible for raising him, while his teenaged, single mother was finishing high school. The witnesses reported that Mr. Simpson's father was not involved in his upbringing and that Mr. Simpson dropped out of school in the eighth grade. The overall theme of the testimony was that Mr. Simpson had a good family who loved and supported him, but could not provide all the guidance required in raising him and his two siblings. Mr. Simpson's grandmother, mother, aunt, and ex-girlfriend all testified they would continue to support Mr. Simpson and would visit him in prison, if his life was spared. Following the sentencing trial, the jury found all four aggravating factors by special verdict and recommended a sentence of death for each murder. The court adopted the jury's recommendation and sentenced Mr. Simpson to death. b. Appellate and post-conviction proceedings Mr. Simpson appealed his convictions and sentences, alleging a variety of errors in both the guilt and sentencing stages of his trial. On direct appeal, the OCCA affirmed Mr. Simpson's convictions and death sentences as to both Mr. Palmer and Mr. Jones. Simpson I , 230 P.3d at 907. Although the OCCA struck the HAC Aggravator for the death of Mr. Jones, it concluded no constitutional error had occurred and no relief was warranted because the jury had not considered any evidence admitted solely due to the erroneous inclusion of that aggravating factor. Id. at 902-03. Simultaneous with his direct appeal, Mr. Simpson filed an application for post-conviction relief and an application for an evidentiary hearing on whether he had received ineffective assistance of trial counsel. Simpson v. State (Simpson II ), No. PCD-2007-1262 (Okla. Crim. App. Oct. 13, 2010) (unpublished). The OCCA denied both applications. Three years later, Mr. Simpson filed a second state application for post-conviction relief, coupled with another application for an evidentiary hearing, in order to exhaust claims presented in his federal habeas petition. Again, the OCCA denied both applications. See Simpson v. State (Simpson III ), No. PCD-2012-242 (Okla. Crim. App. Mar. 8, 2013) (unpublished). 2. Federal Court Proceedings Mr. Simpson sought federal post-conviction relief by filing a petition for a writ of habeas corpus pursuant to 28 U.S.C. § 2254, a motion for discovery, and a motion for an evidentiary hearing. See Simpson v. Duckworth (Simpson IV ), No. CIV-11-96-M, 2016 WL 3029966, at *1 (W.D. Okla. May 25, 2016) (unpublished). The district court denied his petition and motions, but granted a Certificate of Appealability ("COA") on two of the eighteen grounds for relief: (1) the trial court's alleged improper exclusion of Mr. Simpson's PTSD evidence from the guilt stage of the trial and (2) an alleged Brady violation, whereby prosecutors withheld impeachment evidence as to Mr. Collins. This court subsequently granted a COA on five additional issues: (1) whether alleged prosecutorial misconduct denied Mr. Simpson a fundamentally fair sentencing proceeding; (2) whether a jury instruction and prosecutorial statements unduly limited jury consideration of mitigating evidence; (3) whether the HAC aggravating factor determination as to Mr. Palmer was unconstitutional and unreasonable; (4) whether trial counsel was ineffective for failing to investigate, prepare, and present lay witnesses, failing to request a second-degree murder instruction, failing to object to improper prosecutorial arguments, failing to object to the HAC instruction, and failing to object to the jury instruction limiting consideration of mitigating evidence; and (5) whether there was "cumulative error, limited to errors in the grounds on which a certificate of appealability has been granted." Case Management Order dated December 1, 2016. II. STANDARD OF REVIEW AEDPA requires that we apply a "difficult to meet and highly deferential standard" in federal habeas proceedings under 28 U.S.C. § 2254 ; it is one that "demands that state-court decisions be given the benefit of the doubt." Cullen v. Pinholster , 563 U.S. 170, 181, 131 S.Ct. 1388, 179 L.Ed.2d 557 (2011) (internal quotation marks omitted). When a petitioner includes in his habeas application a "claim that was adjudicated on the merits in State court proceedings," a federal court shall not grant relief on that claim unless the state-court decision: (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 unreasonable determination of the facts in light of the evidence presented in the State court proceeding. 28 U.S.C. § 2254(d)(1)-(2). Section 2254(d)(1) 's reference to "clearly established Federal law, as determined by the Supreme Court of the United States," "refers to the holdings, as opposed to the dicta, of th[e] Court's decisions as of the time of the relevant state-court decision." Williams v. Taylor , 529 U.S. 362, 412, 120 S.Ct. 1495, 146 L.Ed.2d 389 (2000). "Federal courts may not extract clearly established law from the general legal principles developed in factually distinct contexts, and Supreme Court holdings must be construed narrowly and consist only of something akin to on-point holdings." Fairchild v. Trammell (Fairchild I ), 784 F.3d 702, 710 (10th Cir. 2015) (internal quotation marks omitted). Under § 2254(d)(1), a state-court decision is "contrary to" the Supreme Court's clearly established precedent if it "applies a rule that contradicts the governing law set forth in [Supreme Court] cases" or if it "confronts a set of facts that are materially indistinguishable from a decision of th[e] Court and nevertheless arrives at a result different from [that] precedent." Williams , 529 U.S. at 405-06, 120 S.Ct. 1495. A state court need not cite, or even be aware of, applicable Supreme Court decisions, "so long as neither the reasoning nor the result of the state-court decision contradicts them." Early v. Packer , 537 U.S. 3, 8, 123 S.Ct. 362, 154 L.Ed.2d 263 (2002) (per curiam). A state-court decision is an "unreasonable application" of Supreme Court law if the decision "correctly identifies the governing legal rule but applies it unreasonably to the facts of a particular prisoner's case." Williams , 529 U.S. at 407-08, 120 S.Ct. 1495. We undertake this "objective[ ] unreasonable[ness]" inquiry, id. at 409, 120 S.Ct. 1495, in view of the specificity of the governing rule: "The more general the rule, the more leeway courts have in reaching outcomes in case-by-case determinations," Yarborough v. Alvarado , 541 U.S. 652, 664, 124 S.Ct. 2140, 158 L.Ed.2d 938 (2004). Conversely, "[i]f a legal rule is specific, the range may be narrow" and "[a]pplications of the rule may be plainly correct or incorrect." Id. And "an unreasonable application of federal law is different from an incorrect application of federal law." Williams , 529 U.S. at 410, 120 S.Ct. 1495. As a result, "a federal habeas court may not issue the writ simply because that court concludes in its independent judgment that the relevant state-court decision applied clearly established federal law erroneously or incorrectly"; "that application must also be unreasonable." Id. at 411, 120 S.Ct. 1495. Claims not "adjudicated on the merits" in state court are entitled to no deference. Fairchild I , 784 F.3d at 711. But, "even in the setting where we lack a state court merits determination, '[a]ny state-court findings of fact that bear upon the claim are entitled to a presumption of correctness rebuttable only by "clear and convincing evidence." ' " Grant v. Royal , 886 F.3d 874, 889 (10th Cir. 2018) (quoting 28 U.S.C. § 2254(e)(1) ) (alteration in original), petition for cert. filed sub nom. Grant v. Carpenter , No. 18-6713 (Nov. 13, 2018); see also Hooks v. Ward (Hooks I ), 184 F.3d 1206, 1223 (10th Cir. 1999) (presuming correctness of state court findings on claim not adjudicated on the merits). Although the burdens on the petitioner under AEDPA are significant, we "undertake this review cognizant that our duty to search for constitutional error with painstaking care is never more exacting than it is in a capital case." Fairchild v. Workman (Fairchild II ), 579 F.3d 1134, 1140 (10th Cir. 2009) (internal quotation marks omitted). With these standards in mind, we turn to Mr. Simpson's claims. III. DISCUSSION As discussed, Mr. Simpson raises seven grounds for relief. We consider each of his arguments in turn. A. Right to Present a Complete Defense Mr. Simpson first asserts he is entitled to federal habeas relief with respect to his convictions because the trial court erroneously excluded expert testimony regarding his PTSD diagnosis and dissociative episodes from the guilt stage of trial. Mr. Simpson claims Dr. Massad's testimony was necessary to support the defense that his PTSD, standing alone or in conjunction with his intoxication defense, rendered him incapable of forming the specific intent to kill. According to Mr. Simpson, excluding this evidence violated his constitutional right to present a complete defense. We begin our review of this claim by providing additional factual and procedural background. We then address the State's arguments that the claim is unexhausted and unpreserved. Deciding that the PTSD portion of Mr. Simpson's claim is properly preserved and has been exhausted, we then examine the OCCA's merits decision. We conclude that decision is not unreasonable under § 2254(d)(1), and we therefore deny Mr. Simpson relief on this claim. 1. Additional Factual and Procedural Background In reviewing this claim, the OCCA examined the transcript of the trial court hearing on the exclusion of the evidence and Dr. Massad's testimony during the sentencing stage of Mr. Simpson's trial. The OCCA concluded the trial court did not abuse its discretion by excluding this testimony from the guilt stage of trial because Dr. Massad could not say how Mr. Simpson's PTSD affected his ability to form the intent to kill. Simpson I , 230 P.3d at 895. As a result, the OCCA held that Mr. Simpson's PTSD diagnosis was "neither relevant to the intent element of the crime charged nor was it relevant to his defense of voluntary intoxication." Id. On federal habeas review, Mr. Simpson challenges the OCCA's determination as both contrary to and an unreasonable application of clearly established federal law. The State counters that Mr. Simpson is barred from presenting this claim because he has failed to exhaust available state court remedies, he has forfeited the argument he makes on appeal by not presenting it to the district court, and, alternatively, because the OCCA's decision was neither contrary to federal law nor unreasonable. 2. Exhaustion and Preservation We begin our analysis with the state's argument that Mr. Simpson failed to exhaust his claim that the trial court violated his right to present a complete defense. See United States v. Miller , 868 F.3d 1182, 1185 (10th Cir. 2017). a. Legal standard AEDPA permits federal courts to entertain only those applications for a writ of habeas corpus alleging that a person is in state custody "in violation of the Constitution or laws or treaties of the United States." 28 U.S.C. § 2254(a). A federal court may not grant such an application unless, with certain exceptions not relevant here, the applicant has exhausted state remedies before filing his petition. Id. § 2254(b) - (c) ; see Pinholster , 563 U.S. at 181, 131 S.Ct. 1388. In general, to exhaust state remedies, a petitioner "must give the state courts an opportunity to act on his claims before he presents those claims to a federal court in a habeas petition." Thacker v. Workman , 678 F.3d 820, 839 (10th Cir. 2012) (quoting O'Sullivan v. Boerckel , 526 U.S. 838, 842, 119 S.Ct. 1728, 144 L.Ed.2d 1 (1999) ). This is accomplished by providing "the state courts one full opportunity to resolve any constitutional issues by invoking one complete round of the State's established appellate review process." Id. (quoting O'Sullivan , 526 U.S. at 845, 119 S.Ct. 1728 ). A claim is exhausted only after "it has been 'fairly presented' to the state court." Bland v. Sirmons , 459 F.3d 999, 1011 (10th Cir. 2006) (quoting Picard v. Connor, 404 U.S. 270, 275, 92 S.Ct. 509, 30 L.Ed.2d 438 (1971) ). "Fair presentation" requires that the substance of the federal claim was raised in state court. Id. "The petitioner need not cite 'book and verse on the federal constitution,' but the petitioner cannot assert entirely different arguments from those raised before the state court." Id. (quoting Picard , 404 U.S. at 278, 92 S.Ct. 509 ). Under this standard, Mr. Simpson's claim is unexhausted if the substance of the claim he is arguing here is different from the argument he made to the OCCA. Turning to preservation, "[a] federal appellate court will not consider an issue not passed upon below." F.D.I.C. v. Noel , 177 F.3d 911, 915 (10th Cir. 1999) (quoting Singleton v. Wulff , 428 U.S. 106, 120, 96 S.Ct. 2868, 49 L.Ed.2d 826 (1976) ). "Consequently, when a litigant fails to raise an issue below in a timely fashion and the court below does not address the merits of the issue, the litigant has not preserved the issue for appellate review." Id. To properly raise an argument below, a litigant must present the argument "with sufficient clarity and specificity." Folks v. State Farm Mut. Auto. Ins. Co. , 784 F.3d 730, 741 (10th Cir. 2015). To this point, "vague, arguable references to a point in the district court proceedings do not preserve the issue on appeal ... because such perfunctory presentation deprives the trial court of its opportunity to consider and rule on an issue in any detail." Id. (citation and internal quotation marks omitted). b. Analysis Before this court, Mr. Simpson contends he suffers from dissociative episodes, and that his PTSD was the result of being shot by his friend and a lifetime of trauma. The State asserts Mr. Simpson's claim is unexhausted and unpreserved because he is presenting an entirely different theory to this court than the theory he presented to the OCCA and the district court. The State further asserts Mr. Simpson has improperly supplemented his argument on appeal by relying on facts raised in conjunction with his ineffective assistance of counsel claim. Mr. Simpson disagrees, stating, "his argument throughout has been that his PTSD, not malice aforethought, is what caused him to react the way he did." Aplt. Reply Br. at 3-5. He further contends his claim is supportable even without the additional facts about his violent upbringing, and that the evidence of dissociative episodes is not new because the description of the phenomenon, if not the name itself, was presented to the OCCA. For purposes of discussion, we divide Mr. Simpson's argument into two categories: (1) PTSD evidence and (2) evidence of dissociative episodes. We conclude that Mr. Simpson properly preserved and exhausted his PTSD argument, but that he failed to properly preserve his argument concerning dissociative episodes. i. PTSD evidence On direct appeal, Mr. Simpson argued his PTSD was the result of a single event-his having previously been ambushed and shot by his friend. Mr. Simpson further claimed his PTSD was "relevant to the issue of whether he shot with malice aforethought, or did so out of a sense of exaggerated fear and terror caused by his PTSD," which was exacerbated by his consumption of drugs and alcohol on the night of the murders. Aplt. Br. at 22-23, Simpson I , 230 P.3d 888 (No. D-2007-1055). Thus, Mr. Simpson posited that evidence of his PTSD would have negated his ability to form the specific intent necessary to commit first-degree murder. Finally, Mr. Simpson argued his PTSD was relevant to support his voluntary intoxication defense. Although Mr. Simpson's position in this court is more refined than the argument he made to the OCCA, the core of his PTSD claim is the same. His assertion that the OCCA's decision was "unreasonable based on [the OCCA and trial court's] misunderstanding of PTSD" is not a new claim, but rather an attempt to bolster his consistently-advanced position that his PTSD diagnosis was relevant as a defense during the guilt stage of trial. Compare Aplee. Br. at 14-29, with Simpson I , 230 P.3d at 894-95. It is true that Mr. Simpson has presented this court with additional evidence to support a diagnosis of trauma-related PTSD, but he also correctly notes that Dr. Massad was aware of enough evidence before trial to diagnose Mr. Simpson with PTSD and in fact did so. Thus, Mr. Simpson's claim that the symptoms of his PTSD-specifically the tendency to overreact-prevented him from forming the requisite intent to kill has been exhausted. The State also asserts that Mr. Simpson has failed to preserve this claim on appeal by failing to raise it in the district court. The district court described Mr. Simpson's PTSD argument as follows: In Ground 2, [Mr. Simpson] asserts that he is entitled to habeas relief because the trial court prevented him from presenting evidence in the guilt stage that he suffered from Post Traumatic Stress Disorder (PTSD). [Mr. Simpson] argues that this evidence was relevant to the issue of intent and his voluntary intoxication defense, and that because he was unable to present this evidence, he was denied his constitutional right to present a complete defense. Simpson IV , 2016 WL 3029966, at *6. Thus, Mr. Simpson advanced his PTSD argument before the district court. Accordingly, we reject the State's failure-to-preserve argument and determine Mr. Simpson's PTSD argument is properly before us. ii. Dissociative episodes In this court, Mr. Simpson also attempts to introduce a new defense related to, but qualitatively different than, the PTSD defense he raised before the district court. In his argument to this court, Mr. Simpson contends he "was in the midst of a PTSD and/or dissociative episode during the crime[, which] reveals his brain was functioning such that either he had a reduced capacity to form the specific intent of first-degree malice aforethought murder, or he was unable to form the intent at all." Aplt. Br. at 24. To be sure, Mr. Simpson argued to the district court that his PTSD, combined with his drug and alcohol abuse, prevented him from forming the requisite mens rea. See Aplt. Br. at 14, Simpson IV , 2016 WL 3029966 (No. CIV-11-96-M) (arguing that PTSD can cause someone to "react out of an exaggerated sense of fear and terror uncontrolled by one's will" and "that the level of intoxication necessary to negate the specific intent of first-degree, malice aforethought murder is affected by PTSD"). But nowhere did he suggest, before his argument here, that he suffered from a dissociative episode at the time of the murders that rendered him "unable to form the intent at all." Accordingly, we agree with the State that Mr. Simpson failed to preserve any claim that he was in a dissociative state at the time of the murders. We therefore confine our analysis of this claim to Mr. Simpson's PTSD argument. 3. Merits We turn now to the merits of Mr. Simpson's assertion that the trial court violated his constitutional right to present a complete defense when it excluded evidence that his PTSD made him hypervigilant and, together with his substance abuse on the night of the murders, rendered him incapable of forming the requisite mens rea. See Crane v. Kentucky , 476 U.S. 683, 690, 106 S.Ct. 2142, 90 L.Ed.2d 636 (1986) ; Washington v. Texas , 388 U.S. 14, 18-19, 87 S.Ct. 1920, 18 L.Ed.2d 1019 (1967). Mr. Simpson raises two distinct claims of error in this regard. First, he contends the trial court erred by refusing to allow him to present a defense theory that PTSD negated his ability to form the specific intent required for first-degree murder. Second, he argues evidence establishing that he suffered from PTSD was required to assist the jury in understanding the voluntary intoxication instruction. a. OCCA decision The OCCA rejected both of these arguments on direct appeal, finding Dr. Massad's testimony irrelevant in both situations because he "could not testify as to how [Mr. Simpson's] PTSD could affect his intent at the time of the crime." Simpson I , 230 P.3d at 895. The OCCA decided this claim on the merits, thereby triggering AEDPA deference. According to Mr. Simpson, the OCCA's decision contradicted and unreasonably applied Supreme Court law. b. Reasonableness of the OCCA's legal determination The Supreme Court has recognized that although criminal defendants have the right to present a complete defense, they must still comply with a state's well-established rules of evidence. See Holmes v. South Carolina , 547 U.S. 319, 326, 126 S.Ct. 1727, 164 L.Ed.2d 503 (2006). Oklahoma law therefore informs our analysis. i. PTSD as a stand-alone defense As relevant to Mr. Simpson's first argument-that PTSD negated specific intent-the trial court correctly noted that Oklahoma permits diminished capacity evidence only in the case of an intoxication or insanity defense. Frederick v. State , 37 P.3d 908, 931 (Okla. Crim. App. 2001). Mr. Simpson claims Oklahoma's rule is contrary to clearly established federal law because a diagnosis of PTSD is relevant in assessing whether the individual formed the specific intent necessary for first-degree murder. But Mr. Simpson fails to identify a single federal case, let alone a Supreme Court case, supporting his position. Where there is no Supreme Court case on point, there is no clearly established federal law for the purposes of AEDPA. See Hooks v. Workman (Hooks II ), 689 F.3d 1148, 1176 (10th Cir. 2012). And when a defendant "is unable to find any 'clearly established' Supreme Court precedent in support of [his] claim[,] ... habeas relief is impossible to obtain." Miller-El v. Cockrell , 537 U.S. 322, 350, 123 S.Ct. 1029, 154 L.Ed.2d 931 (2003). As such, Mr. Simpson's claim "fails at the threshold for lack of clearly established federal law." Hooks II , 689 F.3d at 1176. ii. PTSD as support for the intoxication defense Alternatively, Mr. Simpson argues the trial court erred by excluding Dr. Massad's testimony because it was necessary to assist the jury in evaluating Mr. Simpson's intoxication defense. The OCCA held that, because Dr. Massad's testimony was irrelevant, the trial court did not abuse its discretion in excluding it. Simpson I , 230 P.3d at 895. This decision is reasonable under AEDPA unless no fairminded jurist could agree the evidence was irrelevant. See Harrington v. Richter , 562 U.S. 86, 102, 131 S.Ct. 770, 178 L.Ed.2d 624 (2011). Under Oklahoma law, evidence is relevant if it "ha[s] any tendency to make the existence of any fact that is of consequence to the determination of the action more or less probable than it would be without the evidence." Okla. Stat. tit. 12, § 2401. And, "expert opinion testimony should be admitted only if it will 'assist the trier of fact to understand the evidence or to determine a fact in issue.' " Hooks v. State (Hooks III ), 862 P.2d 1273, 1278 (Okla. Crim. App. 1993) (quoting Okla. Stat. tit.12, § 2702). "When a defendant raises the defense of voluntary intoxication, an expert may properly offer his or her opinion on whether the defendant's actions were intentional." Coddington v. State , 142 P.3d 437, 450 (Okla. Crim. App. 2006). Thus, under Coddington , Dr. Massad "could have properly testified that, in his opinion and based upon his specialized knowledge, he believed [Mr. Simpson] would have been unable to form the requisite deliberate intent of malice aforethought." See id. But, "[w]here the normal experiences and qualifications of laymen jurors permit them to draw proper conclusions from the facts and circumstances, expert conclusions or opinions are inadmissible." Hooks III , 862 P.2d at 1279 (quoting Gabus v. Harvey , 678 P.2d 253, 256 (Okla. 1984) ). The relevancy of Mr. Simpson's PTSD diagnosis, therefore, turns on whether Dr. Massad's testimony would have assisted the jury in determining whether Mr. Simpson's "intoxication affected his mental state and prevented him from forming malice aforethought." See White v. State , 973 P.2d 306, 311 (Okla. Crim. App. 1998). We have further explained that although, "psychological or psychiatric evidence that negates the essential element of specific intent can be admissible[,] [t]he admission of such evidence will depend upon whether [it] ... would negate intent rather than merely present a dangerously confusing theory of defense more akin to justification and excuse." United States v. Brown , 326 F.3d 1143, 1147 (10th Cir. 2003). A review of Dr. Massad's testimony fails to demonstrate any meaningful connection between PTSD and intent generally, or intoxication specifically. Even a generous reading of his testimony demonstrates only a bare assertion that Mr. Simpson had PTSD and that PTSD could cause one to be hypervigilant and to overreact to stimuli. Dr. Massad's testimony lacked any detail on the impact Mr. Simpson's PTSD had on his ability to form the intent to kill, and Dr. Massad's testimony on the interactive effects of PTSD and intoxicants is similarly lacking. Dr. Massad opined that PTSD could be affected by drugs and alcohol because they "could lower one's defenses and increase the likelihood that [the person] would react or overreact." Trial Tr. vol. 7 at 167. On cross-examination, however, Dr. Massad admitted he was "not sure about how the brain and alcohol interact" beyond generally lowering a person's inhibitions-which occurs regardless of "whether or not they have PTSD." Id. at 183. This is not the type of specialized knowledge beyond the "normal experiences and qualifications of laymen jurors." See Hooks III , 862 P.2d at 1279. And without more, this testimony falls within the "justification and excuse" evidence cautioned against in Brown , 326 F.3d at 1147. Because a fairminded jurist could agree that Dr. Massad's testimony was irrelevant, the OCCA's decision was reasonable. B. Brady Claim Mr. Simpson next alleges the prosecutors violated their constitutional responsibility under Brady v. Maryland to disclose all evidence favorable to the defense. Specifically, he contends the prosecution suppressed impeachment evidence against a State sentencing-stage witness, Roy Collins. In addressing this claim, we begin with a discussion of what Brady requires. We then provide additional background relevant to the OCCA's decision, concluding that the OCCA did not resolve this claim on the merits. Instead, the OCCA held that Mr. Simpson waived his Brady claim by not bringing it on direct appeal or in his first state post-conviction application. We next consider whether Mr. Simpson can overcome that state procedural bar and conclude he cannot. As a result, we affirm the district court's denial of relief on this claim. Finally, we consider Mr. Simpson's request for discovery and an evidentiary hearing before the district court and we deny relief on that request, as well. 1. Elements of a Brady Claim We have recognized three essential elements of a Brady claim: (1) the prosecutor suppressed the evidence; (2) the suppressed evidence was favorable to the accused, either because it is exculpatory or because it is impeaching; and (3) prejudice ensued because the suppressed evidence was material. See Scott v. Mullin , 303 F.3d 1222, 1230 (10th Cir. 2002) ; see also Banks v. Dretke , 540 U.S. 668, 691, 124 S.Ct. 1256, 157 L.Ed.2d 1166 (2004) (" Banks ( Dretke )") (quoting Strickler v. Greene , 527 U.S. 263, 281-82, 119 S.Ct. 1936, 144 L.Ed.2d 286 (1999) ). Evidence is suppressed for Brady purposes if the prosecution fails to disclose favorable exculpatory or impeachment evidence known either by it or the police, "irrespective of the good faith or bad faith of the prosecution." Wearry v. Cain , --- U.S. ----, 136 S.Ct. 1002, 1006-07 & 1007 n.8, 194 L.Ed.2d 78 (2016). "Favorable evidence 'is material if there is a reasonable probability that, had the evidence been disclosed to the defense, the result of the proceeding would have been different.' " Douglas v. Workman , 560 F.3d 1156, 1173 (10th Cir. 2009) (quoting Kyles v. Whitley , 514 U.S. 419, 433, 115 S.Ct. 1555, 131 L.Ed.2d 490 (1995) ). Here, Mr. Simpson claims the State suppressed three pieces of evidence (collectively, the "Collins Evidence"): (1) a video-taped interview with Roy Collins from January 5, 2006, which reveals Mr. Collins's Hoover Crips gang affiliation and calls into question the veracity of his testimony concerning Mr. Simpson's jailhouse statements by revealing that Mr. Collins made nearly identical jailhouse statements about Jason Whitecrow, a defendant in an unrelated criminal trial; (2) Mr. Collins's complete arrest, conviction, and incarceration records that reveal an additional four convictions to which Mr. Collins did not testify at trial; and (3) statements reflecting Mr. Collins's expectation of prosecutorial assistance in exchange for his testimony. According to Mr. Simpson, the Collins Evidence was materially favorable Brady evidence that could have cast doubt on the credibility of Mr. Collins's testimony, which, in turn, was critical to support the Continuing Threat Aggravator. See Giglio v. United States , 405 U.S. 150, 154, 92 S.Ct. 763, 31 L.Ed.2d 104 (1972) ; Douglas , 560 F.3d at 1172-73. If Mr. Simpson can make this showing, "the prosecution's failure to disclose [the Collins Evidence] was harmful as a matter of law [and] 'there is no need for further harmless-error review.' " See Banks v. Reynolds , 54 F.3d 1508, 1522 (10th Cir. 1995) (" Banks ( Reynolds )") (citation omitted) (quoting Kyles , 514 U.S. at 435, 115 S.Ct. 1555 ); see also Douglas , 560 F.3d at 1173. 2. OCCA Decision Mr. Simpson did not present his Brady claim to the OCCA until his second application for post-conviction relief. The OCCA held the claim was procedurally barred because the misconduct happened at trial, the legal basis for the claim was available on direct appeal and on the first post-conviction application, and "the factual basis for the claim[ ] was available and could have been ascertained through the exercise of reasonable diligence." Simpson III , slip op. at 4 (citing Okla. Stat. tit. 22, § 1089(D) ). Specifically, the OCCA ruled Mr. Simpson's Brady claim had been waived. Id. 3. Procedural Default a. Independent and adequate procedural bar Under the doctrine of procedural default, "[c]laims that are defaulted in state court on adequate and independent state procedural grounds will not be considered by a habeas court...." Fairchild II , 579 F.3d at 1141 (quotation marks omitted); see also Martinez v. Ryan , 566 U.S. 1, 9, 132 S.Ct. 1309, 182 L.Ed.2d 272 (2012) ("[A] federal court will not review the merits of claims, including constitutional claims, that a state court declined to hear because the prisoner failed to abide by a state procedural rule."). "To be adequate, the [state] procedural ground must be strictly or regularly followed and applied evenhandedly to all similar claims." Thacker, 678 F.3d at 835 (internal quotation marks omitted). We have previously determined that Oklahoma's procedural default rule in title 22, section 1089(D) of the Oklahoma Statutes meets this requirement. See, e.g., id. at 835-36. In turn, a state procedural rule is independent "if it relies on state law, rather than federal law, as the basis for decision." Banks v. Workman , 692 F.3d 1133, 1145 (10th Cir. 2012) (quotation marks omitted). Here, the OCCA relied only on its state procedural rule, § 1089(D), to conclude that Mr. Simpson's Brady claim was waived. Thus, "we must recognize the OCCA's waiver ruling and treat the claim as procedurally barred for purposes of federal habeas review." Thacker , 678 F.3d at 836. Consequently, Mr. Simpson's Brady claim is precluded from federal habeas review unless he can overcome the default. b. Legal background on cause and prejudice "A prisoner may obtain federal review of a defaulted claim by showing cause for the default and prejudice from a violation of federal law." Martinez , 566 U.S. at 10, 132 S.Ct. 1309 ; see also Fairchild II , 579 F.3d at 1141. To establish "cause," a petitioner must show that "some objective factor external to the defense impeded [his] efforts to comply with the State's procedural rule." Scott , 303 F.3d at 1228 (quoting Murray v. Carrier , 477 U.S. 478, 488, 106 S.Ct. 2639, 91 L.Ed.2d 397 (1986) ). Such objective factors include "a showing that the factual or legal basis for a claim was not reasonably available to counsel, or that some interference by officials made compliance impracticable." Id. (quoting Murray , 477 U.S. at 488, 106 S.Ct. 2639 ). A petitioner must also show " 'actual prejudice' resulting from the errors of which he complains." United States v. Frady , 456 U.S. 152, 168, 102 S.Ct. 1584, 71 L.Ed.2d 816 (1982) ; see also Thacker , 678 F.3d at 835. Because "cause and prejudice parallel two of the three components of the alleged Brady violation itself," Strickler , 527 U.S. at 282, 119 S.Ct. 1936, if Mr. Simpson can successfully demonstrate cause and prejudice, he will have also succeeded in establishing his Brady claim, see Banks (Dretke ), 540 U.S. at 691, 124 S.Ct. 1256 ; see also Scott , 303 F.3d at 1230 ("[W]e conclude that the ... statements constitute Brady evidence that the prosecution had a duty to disclose to [petitioner]. Therefore [petitioner] has also established prejudice to overcome his procedural default."). We therefore address the Brady and procedural bar factors together. Mr. Simpson must establish both cause and prejudice to overcome the state procedural bar, and we must reject his Brady claim if he fails to show either requirement. See McCleskey v. Zant, 499 U.S. 467, 502, 111 S.Ct. 1454, 113 L.Ed.2d 517 (1991) ("As [petitioner] lacks cause for failing to raise the Massiah claim in the first federal petition, we need not consider whether he would be prejudiced by his inability to raise the alleged Massiah violation at this late date." (citing Murray , 477 U.S. at 494, 106 S.Ct. 2639 ) ); see also Coleman v. Thompson , 501 U.S. 722, 757, 111 S.Ct. 2546, 115 L.Ed.2d 640 (1991) (holding petitioner's claim barred by state procedural default where petitioner could not establish cause, without considering prejudice); Romano v. Gibson , 239 F.3d 1156, 1171-72 (10th Cir. 2001) (assuming the State suppressed Brady evidence but denying relief because the evidence was not material). We exercise our discretion to proceed directly to the prejudice/materiality question. Ultimately, we deny Mr. Simpson relief on his Brady claim because, even assuming he could show cause/suppression, he cannot establish prejudice/materiality. c. Prejudice/Materiality merits analysis "[P]rejudice within the compass of the 'cause and prejudice' requirement exists when the suppressed evidence is 'material' for Brady purposes." Banks (Dretke ), 540 U.S. at 691, 124 S.Ct. 1256. Suppressed evidence "is material if there is a reasonable probability that, had the evidence been disclosed to the defense, the result of the proceeding would have been different." Id. (quoting Kyles , 514 U.S. at 433, 115 S.Ct. 1555 ). "A 'reasonable probability' is a 'probability sufficient to undermine confidence in the outcome.' " Scott , 303 F.3d at 1230 (quoting United States v. Bagley , 473 U.S. 667, 682, 105 S.Ct. 3375, 87 L.Ed.2d 481 (1985) ). "In evaluating the materiality of withheld evidence, we do not consider each piece of withheld evidence in isolation. Rather we review the cumulative impact of the withheld evidence, its utility to the defense as well as its potentially damaging impact on the prosecution's case." Banks (Reynolds ), 54 F.3d at 1518 ; see also Snow v. Sirmons , 474 F.3d 693, 711 (10th Cir. 2007). Put another way, "we evaluate the materiality of withheld evidence in light of the entire record in order to determine if 'the omitted evidence creates a reasonable doubt that did not otherwise exist.' " Banks (Reynolds ), 54 F.3d at 1518 (quoting United States v. Agurs , 427 U.S. 97, 112, 96 S.Ct. 2392, 49 L.Ed.2d 342 (1976) ). Here, even if all the evidence Mr. Simpson claims is material had been disclosed, there is no reasonable probability the jury would have decided on a sentence less than death. See Douglas , 560 F.3d at 1173. The suppressed evidence includes: Mr. Collins's prior gang affiliation with the Hoover Crips-the same gang the victims belonged to and the rival of Mr. Simpson's gang, the Bloods; Mr. Collins's additional criminal convictions; the similarities between the two jailhouse confession stories; and Mr. Collins's alleged expectation of prosecutorial assistance in exchange for his testimony. To be sure, this evidence could have been used to impeach Mr. Collins, who testified in support of the Continuing Threat Aggravator. In evaluating prejudice/materiality, however, the impact of the evidence must be viewed in light of the impeachment evidence introduced at trial and the strength of the State's aggravating evidence. See Banks (Reynolds ), 54 F.3d at 1518. The only wholly new information withheld was Mr. Collins's prior gang affiliation and the alleged similarities between Mr. Collins's story of his conversation with Mr. Simpson and his prior testimony in the Whitecrow trial. All of the other Collins Evidence related to topics on which evidence was introduced in some form at trial. For example, the State conceded at trial that Mr. Collins wanted to exchange his testimony for favorable treatment, but claimed it never agreed to such a deal. The State also admitted, and the jury was informed, that Mr. Collins was a liar, a drug dealer, and a criminal, even if the extent of those lies and crimes was not fully disclosed. In particular, the defense established during trial that Mr. Collins lied on the stand about playing football at the University of Oklahoma. It is true the prosecutor attempted to undermine the effectiveness of this impeachment evidence by suggesting that, in Mr. Collins's "drug-induced mind, he thinks he did [play football at the University of Oklahoma]." Trial Tr. vol. 8 at 19. Nonetheless, the defense efforts at trial made the jury aware that Mr. Collins's recollection of events was questionable at best. The introduction of evidence of additional criminal convictions, or of more factual inaccuracies therefore, would have had diminishing returns. That said, when considering the suppressed evidence in light of the impeachment evidence introduced at trial, we agree with Mr. Simpson that the suppressed evidence was not all cumulative. See Case v. Hatch , 731 F.3d 1015, 1042-43 (10th Cir. 2013). As indicated, Mr. Collins's gang affiliation and prior testimony about Mr. Whitecrow's alleged jailhouse admissions were not offered in any form at Mr. Simpson's trial. But that fact alone does not make the suppressed evidence material. To make that assessment, we must evaluate Mr. Collins's testimony in light of the State's case as a whole. See Banks (Reynolds ), 54 F.3d at 1518. As indicated, the State alleged four aggravating factors: 1) the Prior Violent Felony Aggravator, 2) the Risk of Multiple Deaths Aggravator, 3) the HAC Aggravator, and 4) the Continuing Threat Aggravator. Although defense counsel conceded the State had proven beyond a reasonable doubt the first two aggravating factors, counsel argued the State had failed to prove Mr. Palmer's death was especially heinous, atrocious, or cruel or that Mr. Simpson would continue to be a threat in jail. Trial Tr. vol. 8 at 46-47 ("[The prosecutor] told you that he has proven beyond a reasonable doubt all four of the aggravators. I will take issue with him on three and four.... [T]hey didn't prove three and four."). The State relied on Mr. Collins's testimony to prove Mr. Simpson would be a continuing threat. Id. at 15 ("Now, this is where Roy Collins come[s] in. A continuing threat."); id. at 22 ("[W]e offered Roy Collins for continuing threat."). And Mr. Collins's extensive and inflammatory testimony may have been a factor in the jury's verdict of death. But the question is not whether Mr. Collins was beneficial to the prosecution; the question is whether the prosecutor's case was strong enough that, had the evidence impeaching Mr. Collins been disclosed, there is no reasonable probability the jury would have decided on a sentence less than death. See Douglas , 560 F.3d at 1173. We believe it was. Mr. Simpson characterizes Mr. Collins as critical to the State's case in aggravation, claiming, "[Mr.] Collins's testimony that Mr. Simpson tried to hire him to kill [the surviving victim] and assault and threaten witnesses and was utterly remorseless, was the centerpiece of the prosecution's case for death." Aplt. Br. at 53, 77-78. He argues the prosecutor "directed [Mr.] Collins to his theme that [Mr.] Simpson, a high rolling outsider from New Orleans, was a remorseless gangster." Id. at 53. While Mr. Simpson acknowledges there was other evidence to support the Continuing Threat Aggravator, he argues Mr. Collins's testimony was so important that the jury might not have imposed the death penalty without it. To put this argument in context, we must consider the other evidence offered in support of a penalty of death. To begin, Mr. Simpson concedes there was sufficient evidence to support the jury's finding of the first two aggravators: (1) he was convicted previously of a felony involving the use or threat of violence and (2) he knowingly created a great risk of death to more than one person. There is also substantial evidence in the record that supported the Continuing Threat Aggravator, even without considering Mr. Collins's testimony. First, the facts of the crime itself support this aggravator. See Jones v. State , 128 P.3d 521, 549-50 (Okla. Crim. App. 2006) ("Evidence of the callous nature of the crime and the defendant's blatant disregard for the importance of human life supports" the Continuing Threat Aggravator). Mr. Simpson gunned down three men with an assault rifle because one of the victims had punched him nearly an hour earlier. He ordered one of his codefendants, Mr. Dalton, to follow the men for several miles and threatened Mr. Robinson, his other codefendant, when Mr. Robinson initially refused to retrieve the rifle from the trunk. The shooting took place in a residential area, yet Mr. Simpson indiscriminately shot fifteen to twenty rounds into the victims' moving car, forcing it to veer off the road and hit an electrical pole. And as he fled the scene, Mr. Simpson shouted, "I'm a monster. I'm a motherfucking monster. Bitches don't want to play with me." Trial Tr. vol. 4 at 44-46. The State also offered other evidence of Mr. Simpson's callous disregard for human life as support for finding the Continuing Threat Aggravator. For example, immediately following the murders, Mr. Simpson proceeded with his plan to visit some women he had met at Fritzi's. The jury could have reasonably inferred a lack of remorse from this conduct and weighed that attitude in favor of finding Mr. Simpson a continuing threat. Mr. Simpson's attempts to conceal evidence further support a finding that he would be a continuing threat. The record reflects that Mr. Simpson threatened Mr. Dalton's family in an attempt to keep Mr. Dalton from speaking to the police, and that Mr. Simpson's codefendants took his threats seriously. Mr. Simpson's past criminal convictions can also serve as evidence in support of the Continuing Threat Aggravator. See Lockett v. State , 53 P.3d 418, 428 (Okla. Crim. App. 2002). The State relied on Mr. Simpson's previous conviction for armed robbery and offered Mr. Pham's testimony about the facts underlying that offense. Mr. Pham related how Mr. Simpson forced his way into Mr. Pham's home, threatened him with a gun, beat him across the face and back, stole his wallet, forced him onto his knees, and then shot him in the head. Mr. Pham provided powerful evidence supporting a finding that Mr. Simpson would be a continuing threat. Weighing all of the aggravating evidence the State introduced against the previously discussed evidence Mr. Simpson presented in mitigation, we find no reasonable probability that the outcome of the sentencing proceeding would have been different had the Collins Evidence been produced. We do not discount the obvious significance of Mr. Collins's testimony or the State's reliance on it. But given the defense's successful, if admittedly limited, impeachment of Mr. Collins and the compelling nature of the State's other aggravating evidence, Mr. Simpson "has not convinced us that there is a reasonable probability that the jury would have returned a different verdict if [Mr. Collins's] testimony had been [further] impeached or excluded entirely." See Strickler , 527 U.S. at 296, 119 S.Ct. 1936. Therefore, the evidence was not material under Brady , and Mr. Simpson cannot demonstrate prejudice. In summary, because Mr. Simpson cannot establish prejudice, we need not consider whether he could show cause. See McCleskey , 499 U.S. at 502, 111 S.Ct. 1454. In the absence of a showing of both cause and prejudice, Mr. Simpson cannot overcome the state procedural bar and we cannot consider this claim on habeas review. Accordingly, we deny Mr. Simpson relief on his Brady claim. 4. Evidentiary Hearing and Discovery Motions In conjunction with his Brady claim, Mr. Simpson appeals the district court's denial of his motion for an evidentiary hearing and discovery seeking additional impeachment evidence as to Roy Collins. The district court denied the motion after determining that Mr. Simpson "would not be entitled to relief even if Mr. Collins'[s] testimony was completely discounted or excluded." Simpson IV , 2016 WL 3029966, at *41. We review a district court's denial of a motion for discovery or an evidentiary hearing for abuse of discretion. See Fairchild II , 579 F.3d at 1147 (evidentiary hearing standard); Wallace v. Ward , 191 F.3d 1235, 1245 (10th Cir. 1999) (motion for discovery standard). Generally speaking, f