Full opinion text
MARCUS, Circuit Judge: In this capital case, the Commissioner of the Alabama Department of Corrections, Richard F. Allen, appeals from the district court’s order granting in part William Glenn Boyd’s petition for a writ of habeas corpus, filed pursuant to 28 U.S.C. § 2254. The district court granted relief on Boyd’s claim that his trial counsel were constitutionally ineffective during the penalty phase of the trial, holding that trial counsel performed deficiently when they failed to conduct a reasonable investigation of mitigating evidence, particularly concerning his childhood, and, thereafter, failed to present this evidence to the jury and the sentencing judge. Boyd, in turn, cross-appeals from the district court’s rejection of three additional claims: first, that some of the jurors impermissibly considered extra-judicial evidence during their deliberations; second, that the State knew its key witness had perjured himself; and, finally, that his trial counsel rendered ineffective assistance by failing to adequately challenge the testimony offered by a co-conspirator, and failed to seek expert assistance. After thorough review, we affirm in part and reverse in part. Applying the law to the record before us, we conclude that there is no reasonable probability the performance of Boyd’s counsel, even if deficient, prejudiced the outcome of the penalty phase of his trial. Moreover, we can discern no merit in Boyd’s cross-appeal. Accordingly, we reverse the district court’s order granting habeas relief, and remand with instructions to reinstate Boyd’s original sentence. I. Facts and Procedural History A. The Guilt Phase of the Trial The brutal facts surrounding the kidnaping, robbery, and murder of Fred and Evelyn Blackmon are these. The Blackmons disappeared from their home in Anniston, Alabama, on March 26, 1986. Between 9:30 and 10:00 a.m. that morning, Mr. Blackmon, accompanied by a slender white male with long dark hair, cashed a $5,000 check at the drive-in window of an Anniston branch of the First Alabama Bank, where Mr. Blackmon maintained an account. At around 9:00 p.m. that night, Julie Greenwood, petitioner Boyd’s ex-girlfriend and Evelyn Blackmon’s twenty-year-old daughter, returned to the Blackmons’ house, where she lived, only to discover that Fred and Evelyn Blackmon were missing, along with their black Cadillac Eldorado. Two days later, Julie and her father, Wayne Greenwood, filed a missing person’s report with the Anniston Police Department. The Blackmons were never seen alive again. At about 8:40 a.m. on March 26, 1986, the day the Blackmons disappeared, Anniston Police Officer Ken Murphy was on routine patrol in the Blackmons’ neighborhood. He noticed a 1976 white, two-door Chevrolet Camaro illegally parked near the intersection of Sunset and Fairway Drives, a quarter of a mile from the Blackmons’ home. The license plate number on the illegally parked vehicle had been issued to William Glenn Boyd. Soon thereafter, Boyd was arrested on the charge of first degree kidnaping on April 3, 1986. After being advised of his Miranda rights, Boyd signed a waiver-of-rights form and gave a statement to the police concerning the Blackmons’ disappearance. In addition, Anniston Police Officers Robertson and Hall impounded Boyd’s automobile. The same day, the police arrested Robert Milstead, who also gave a statement to the police about the Blackmons. In the afternoon of April 3, 1986, the police- — accompanied by Milstead — went to the locations where each of the Blackmons had been separately killed. At the scene of Mrs. Blackmon’s murder, police found a trail through the woods. Officer Watson discovered bleached hair entwined with white fiber. Watson collected soil and debris samples which contained blood-stained leaves and soil. A .25 caliber shell casing was found close to the blood stain. The hair found near the blood stain later was microscopically compared to a hair sample taken from Mrs. Blackmon’s body and determined to be the same. Mr. Blackmon’s 1985 Cadillac Eldorado was recovered from the Coosa River on April 4, 1986. Fred Blackmon was found dead, stuffed into the trunk of the car. The windows were down, the doors were unlocked, the ignition key was in the on position, and the ear was in first gear. Upon discovering that the car’s tail light was broken, the officers went to the area in Calhoun County where Milstead said Mr. Blackmon had been murdered. At that location, in the middle of a dirt road, the officers found broken pieces of a red plastic tail light lens, a silver plastic Cadillac emblem, two spent .25 caliber shell casings, and a long white fiber. On the same day the Blackmons’ car was recovered, Officer Townsley went to Milstead’s house, where he discovered an ax and several blue metal drums. The state medical examiner, who performed an autopsy on Mr. Blackmon, found a torn strip of white cloth tied around his mouth as a gag. Mr. Blackmon had been shot twice. One of the gunshots penetrated his neck and the other passed through the heart. Both bullets were recovered. Mr. Blackmon also had suffered a minor blunt force injury to the back of his head. The gun shot wounds were determined to be the cause of his death. Officers Watson and Bradley inventoried the contents of Boyd’s Chevrolet Camaro on April 7, 1986. They found a piece of white and yellow entwined cloth, knotted on one end, with hair entwined in the knot, as well as a black mesh shirt, a pair of blue underwear, a black jacket, and another piece of cloth on the right front floorboard. They also discovered a roll of gauze in the console of the car along with a yellow-gold necklace inside an envelope. The necklace later was identified as belonging to Mrs. Blackmon. Two spent .22 caliber shell casings were found on the dashboard. On April 9, 1986, a metal drum containing Evelyn Blackmon’s body was recovered from the Coosa River too. Mrs. Blackmon’s mouth had been gagged and a piece of cloth had been tied around her ankles. She had sustained three gunshot wounds: a superficial wound to her head; a wound to the right side of her neck; and a wound to her back. Mrs. Blackmon also had sustained a laceration to her right forehead, numerous fractures to her nose and face, and an ax wound to her lower back that broke her backbone. The gunshot wounds were determined to be the cause of her death. At trial, there was conflicting testimony regarding whether Boyd had murdered Fred Blackmon, Evelyn Blackmon, or both victims. Anniston Police investigator Gary Carroll testified that Boyd insisted in his first statement to the police that his accomplice, Milstead, had killed both victims. Specifically, Boyd told the police that on the morning of March 26, 1986, he and Milstead, both armed, gained entry into the Blackmons’ home. Boyd and Milstead had previously discussed robbing the Blackmons. Boyd admitted that he accompanied Mr. Blackmon to the bank, where Mr. Blackmon withdrew $5,000 and turned it over to Boyd, and returned to the Blackmons’ house. Boyd and Milstead then forced the Blackmons into Mr. Blackmon’s Cadillac Eldorado and drove to an area in Ohatchee, Alabama, near the river. After the car was parked, Milstead, according to Boyd, physically assaulted Mrs. Blackmon, and then shot her. Mr. Blackmon tried to barter for his life, but Boyd hit him on the back of the head, and then Milstead shot him too. Boyd and Milstead left the crime scene in the Cadillac Eldorado, only to return later that night. They stuffed Mr. Blackmon’s body in the trunk of the Cadillac Eldorado and rolled the car down a boat ramp into the river. They left and returned to the crime scene still again the next morning, stuffed Mrs. Blackmon’s body into a 55-gallon barrel and rolled the barrel into the river. They later disposed of the two guns used during the crime by throwing them into a creek. On April 4, 1986, Boyd gave a second statement to the police that provided a detailed description of how to find the locations of the crime scenes. Boyd provided a third statement on April 6, 1986, claiming that he had remained in the car with Mr. Blackmon while Milstead took Mrs. Blackmon into the woods. Boyd said that Milstead was just supposed to leave her there, but decided to kill her instead. Boyd accompanied police to a creek on April 11, 1986, to show them where the guns had been discarded after the murders. A nickel-plated Raven Arms Company .25 caliber automatic pistol and a black .22 caliber pistol were recovered. There was one unfired round in the .25 caliber pistol, and five rounds still in the .22 pistol. Milstead’s statements and testimony, on the other hand, said that Boyd had killed both victims. Milstead pleaded guilty to capital murder and testified for the State against Boyd, in exchange for a sentence of life without parole. Prior to testifying, he had given five statements to the police, which varied in certain respects, but four of them consistently accused Boyd of shooting both victims as well as assaulting them. Milstead testified that on the morning of the crime, Milstead, who did not know the Blackmons, gained entry into the Blackmons’ house along with Boyd; they were both armed with loaded pistols. Boyd then gagged and blindfolded Mrs. Blackmon, and threatened the Blackmons that Mrs. Blackmon’s daughter, Julie, had been taken hostage and would be killed if the Blackmons did not pay a ransom. Boyd forced Fred Blackmon to go to the bank to withdraw money, leaving Mrs. Blackmon alone at the house with Milstead. After Mr. Blackmon withdrew $5,000 and gave the money to Boyd, they returned to the home. Boyd and Milstead then forced Fred and Evelyn Blackmon at gunpoint into Mr. Blackmon’s Cadillac Eldorado, and drove them to a secluded area by the river. At that point, they separated the Blackmons, first forcing Mrs. Blackmon to walk away from the car to a clearing behind a brush pile. Boyd then re-gagged and blindfolded Mrs. Blackmon, and, after talking to her, struck Evelyn Blackmon across her forehead and nose with a stick. Mrs. Blackmon screamed, whereupon Boyd tried to strangle her with a cloth. Boyd then shot Mrs. Blackmon with a .22 caliber pistol, which he had muffled with the cloth. After she continued to fight for her life, Boyd took the .25 caliber gun from Mil-stead, who was standing with them, and shot her still again in the back and in the head. Boyd and Milstead returned to the car and drove Mr. Blackmon to another location. After exiting the car, Boyd hit Mr. Blackmon’s head with a stick. This blow also broke the taillight on Mr. Blackmon’s Cadillac. Boyd then took a piece of cloth and started choking Mr. Blackmon with it. When Fred Blackmon struggled for his life and stabbed Boyd with a stick, Boyd took out the .25 caliber pistol and put it to Mr. Blackmon’s throat. Mr. Blackmon begged Boyd not to shoot him, offering to give him $50,000. Boyd told Fred Blackmon that it was too late, and shot him in the chest and neck with the .25 caliber pistol. Boyd and Milstead left the scene in Mr. Blackmon’s car. They returned later that night to the location of Fred Blackmon’s murder, stuffed his body into the trunk of his car, and rolled it into the Coosa River. After a few minutes, the car sank. They threw the two pistols into a creek that night. The next morning, Boyd and Milstead returned to the crime scene, finding Mrs. Blackmon’s body. By Milstead’s account, Boyd said the body was too stiff, so he took Milstead’s ax and tried to cut Mrs. Blackmon’s body in half. Boyd then took the body and broke Evelyn Blackmon’s back, and along with Milstead threw her body into a metal barrel along with some cement blocks and rocks. Boyd cut some holes in the barrel with the ax. He and Milstead rolled the barrel into the river. The barrel sank in the water. Kenny Surrett, who had grown up with Boyd, also testified for the State, providing another conflicting account indicating that Boyd had confided that he had shot Fred Blackmon, but not Mrs. Blackmon. Surrett said that on the night of March 25, 1986, the evening before the Blackmons were kidnaped and murdered, he was with both Boyd and Milstead. Surrett saw, among other things, a chrome or silver .25 caliber automatic pistol in Boyd’s possession. On the night of March 27, 1986, the day after the Blackmons disappeared, Surrett drove to Boyd’s house to collect on a bad check Boyd had given him. Soon after Surrett arrived, Boyd said, “Kenny, I didn’t realize how coldblooded I was.” R739. Boyd then said he had something to tell Surrett. Boyd admitted that he and Milstead had gone to the Blackmons’ house to rob them, and Boyd had taken Mr. Blackmon to the bank where Mr. Blackmon withdrew some money. Mil-stead and Boyd then took the Blackmons to the river. Boyd said he hit Fred Blackmon on the back of his head with a stick and then shot him. Boyd also told Surrett that Milstead hit Mrs. Blackmon in the nose and shot her a couple of times. Boyd confessed that he chopped Mrs. Blackmon’s back with an ax in order to be able to dispose of her body in a barrel. Boyd paid Surrett with money that, Boyd said, he had obtained from Fred Blackmon. A week later, Boyd joked with Surrett about the Blackmons being “at the bottom of the river.” R745. Sharon Johnson, who was dating Boyd at the time of the crime, gave an account of events roughly consistent with Surrett’s. She testified that Milstead told her that he shot Mrs. Blackmon, and Boyd shot Mr. Blackmon. Johnson further said that she saw Boyd with approximately $3,000. The Calhoun County Grand Jury indicted Boyd on eight counts of capital murder on April 25, 1986. The first four counts charged him with murder dux-ing the course of a kidnaping, in violation of Ala. Code § 13A — 5—40(a)(1), and the remaining four counts charged him with murder during the course of a robbery, in violation of § 13A-5-40(a)(2). On March 16, 1987, Boyd’s capital murder trial began. The jury returned verdicts on March 20, 1987, finding Boyd guilty on all eight counts. B. The Sentencing Hearing Before the Jury The penalty phase of the trial begaxx the same day that Boyd was convicted. Although his lawyers had asked for the evening to prepare, the court gave them only “a few minutes.” R966. The prosecutor did not px-esent any evidence at the sentencing heax-ing before the jury, and instead relied on evidence presented at the guilt phase to argue in support of finding two statutory aggravating circumstances: (1) the capital offense had been committed dux-ing a robbery and kidnaping, see Ala.Code § 13A-5-49(4); and (2) the capital offense was especially heinous, atrocious, or cruel when compared to other capital offenses, see id. § 13A-5-49(8). In response, defense counsel presented four witnesses: Cindy Pierce, Boyd’s sister; Geraldine Oliver, Boyd’s mother; Herbert Hicks, a pastor; and Boyd himself. At counsel’s dix-ection, Cindy Pierce had prepared a “life history” of Boyd that she read to the jury. Cindy’s testimony emphasized the following themes: 1. Boyd’s parents divorced when Boyd was two; Boyd’s father went to prison, and attempted to escape from jail, leaving bad publicity and scars for the family; Boyd did not have much contact with his father, and as a result was adversely affected; 2. Boyd’s younger sister was physically and mentally challenged; as she became older, the family, including Boyd, had to put her in physical restraints when she became violent; 3. Boyd grew up in an impoverished setting; at one point, Boyd and a friend burned down the family’s trailer; Boyd was embarrassed by his family’s financial difficulties; 4. Boyd had difficulties in school, ultimately dropping out at sixteen; 5. Boyd’s mother remarried when Boyd was seven; this was difficult because Boyd was close to his mother and did not want to share her with anyone else; Boyd developed “serious problems” with his stepfather, who was “very strict and demanding”; 6. Boyd’s grandfather died when Boyd was fourteen; this was difficult for Boyd as his grandfather essentially served as Boyd’s father; 7. Boyd’s stepfather’s son was a bad influence on Boyd; when they got in trouble, Boyd’s stepfather took his son’s side; 8. At sixteen, Boyd moved to New Mexico to live and work with his great uncle; this was a “great opportunity” but Boyd became mired in debt and was “too immature to take advantage” of the opportunity; Boyd’s grandmother paid off his debt and Boyd returned to Alabama; 9. Boyd had a romantic relationship with Julie Greenwood but Julie’s mother, Evelyn Blackmon, forbade her daughter to date Boyd; 10. Boyd’s sister, Cindy, married when Boyd was nine; Boyd grew very close to Cindy’s husband who became a “brother figure”; 11. Boyd was a loving and caring uncle to Cindy’s two children; 12. Boyd lived with Cindy and her husband after moving out of his mother’s home when he was fourteen but eventually left Cindy’s home because he resented her discipline; 13. Boyd’s grandparents, to whom Boyd was close, were alcoholics; 14. Boyd served six months in jail for burglary when he was eighteen; 15. Boyd attended church as a youth and it was important to him. See R974-91. Cindy also testified that Boyd expressed remorse for the crime and explained that “it was never meant to happen.” R989. Boyd also testified at the sentencing phase, apologizing for “what happened,” and offering that he wished he could undo his actions. R991-92. Boyd’s mother testified that Boyd was “sorry for all the hurt and pain that” he had caused. R993, 998. She described Boyd as a loving and caring person who was always very helpful. She said that she loved her son and tried to “bring him up in the right way.” R997-98. Finally, Pastor Herbert Hicks testified, after visiting Boyd in jail at the request of Boyd’s mother. Pastor Hicks said that Boyd was sorry for his involvement in the crime even though he was “not guilty.” R999-1000. In addition, Boyd “had turned his face to the Lord and ... had made things right with Him.” R1000. Following this testimony, defense counsel said to the jury: “You have heard it all. There’s not much I can add. The decision is yours.” R1002. The jury recommended, by a vote of seven to five, that Boyd be punished by life imprisonment without the possibility of parole. Thereafter, a date for the sentencing hearing before the trial judge was set. C. The Sentencing Hearing Before The Trial Judge The same judge who had presided over Boyd’s trial commenced a sentencing hearing on April 9, 1987, nineteen days after the sentencing hearing before the jury. Alabama employs a trifurcated proceeding for the trial and sentencing of persons charged with capital offenses: (1) the guilt-innocence phase; (2) the penalty phase, during which the jury issues an advisory sentencing verdict based on its evaluation of aggravating and mitigating circumstances, see Ala.Code § 13A-5-46; and, finally, (3) a phase, after the jury has rendered its advisory verdict at the penalty phase, at which time the trial judge orders and receives a presentence investigation report, takes further argument, and may receive additional evidence concerning the aggravating and mitigating factors. Thereafter, the trial judge is obliged to enter written findings as to these factors and impose sentence. See id. § 13A-5-47; Brownlee v. Haley, 306 F.3d 1043, 1050 (11th Cir.2002). At the sentencing hearing before the trial judge, neither Boyd nor the State offered any additional evidence, although both presented arguments in support of their positions. The trial judge then sentenced Boyd to death, and said that a written order would be filed later. In the sentencing order, the trial judge found the existence of two statutory aggravating circumstances: (1) the capital offense was committed while the defendant had been engaged in the commission of robbery and kidnaping, see Ala.Code § 13A-5-49(4); and (2) the capital offense was especially heinous, atrocious, or cruel when compared to other capital offenses, see id. § 13A-5-49(8). The trial judge amplified the second aggravating circumstance with these written findings of fact: (a) Th[e] Defendant invaded the privacy of the victims, threatened to kill their daughter (and step-daughter), robbed them, kidnaped them at gun point from their home, bound and gagged them, took them to a remote area and abused both of them while they were fighting and begging for their lives. (b) The Defendant inflicted severe pain and suffering upon both victims by hitting them on the head and in the face with a large limb while they were tied up and blindfolded. (c) The Defendant shot each victim two or three times after physically abusing them. (d) The Defendant used an ax to cut Evelyn Blackmon so that her body would go into a 55 gallon drum. (e) The Defendant bragged about the killings and about how cold blooded he was. CR201. The trial judge also found one statutory mitigating circumstance: Boyd was twenty years of age on the date of the offense. In addition, the trial judge took into account a non-statutory mitigating circumstance: the fact that Boyd, to some degree, had assisted police in locating the bodies of the victims and the weapons used in the murders. The trial judge also expressly took into account all of the evidence presented concerning Boyd’s “background and character as the same pertains to the mitigating circumstances that should be properly considered by the Court.” CR202. The trial judge explained that the jury’s penalty phase verdict possibly had been influenced by the very emotional testimony offered by Boyd’s sister and mother. Finally, the trial judge concluded that “[wjhile the mitigating circumstances and the jury’s recommendation of life without parole have weighed heavy in the Court’s consideration, this Court does now find, and is convinced beyond a reasonable doubt and to a moral certainty that the aggravating circumstances of this horrible, cold blooded crime as shown and brought before the Court far outweigh the mitigating circumstances shown to the Court.” CR203. D. Background Regarding the Performance of Boyd’s Counsel Boyd was represented at trial by Stephen Levinson and Grant Paris; Mannon Bankston, Jr. assisted. Only Levinson testified as a witness at Boyd’s state habeas court evidentiary hearing (“the Rule 32 hearing”). According to Levinson, none of Boyd’s lawyers had previously handled a capital case. Levinson had practiced for eight years before he represented Boyd, and had handled about six felony jury trials. Levinson felt that he had the primary responsibility for pretrial preparation, although added that he would not be surprised if Grant Paris “felt that it evolved to him.” Vol. 16 at 109. Boyd would not initially speak with Levinson, but they eventually communicated some fifteen to twenty times before trial. As for witnesses, Boyd’s counsel spoke with Boyd’s mother, his sister, his brother, his brother-in-law, and his stepfather. Counsel learned that Boyd’s father left the home when Boyd was about two years old. However, counsel did not talk to any family members about the possibility of neglect or deprivation, and did not obtain any official records about Boyd or his family. Levinson also “possibly” contacted Sharon Johnson, and unsuccessfully tried to contact Kenny Surrett, who feared he would be charged as an accessory if he did not testify against Boyd, since he had taken money from Boyd after the murders. Id. at 110, 118. Co-counsel Paris contacted the pastor. Counsel also hired an “independent” psychologist, Dr. Alan Krichev, to evaluate Boyd, because they did not want Boyd sent to Taylor Harden Secure Medical Facility, a state-run mental health hospital. Dr. Krichev prepared a report concluding that Boyd had not suffered from any mental illness and was competent. The report further opined that “[tjhere were no indications of major psychopathy,” and that Boyd showed a “lack of emotional content but otherwise w[as] not pathological in nature.” Vol. 16 at 157-58. Levinson decided that he would not call Dr. Krichev as a witness, since he “didn’t know how [the report] would help Glenn.” Id. at 116. Levinson admitted that he lacked an understanding of the tests Dr. Krichev performed, which was probably “due to my inability to either understand or ask.” Id. at 156. Levinson suggested that there was “some dissension between the attorneys” about “how we should handle the case, who should do what, and what essentially our strategy or theory of defense was.” Id. at 105. “We didn’t really have a defense strategy other than ... to dispute what Robert Milstead was saying as best we could with what we had.” Id. at 126. Although Levinson thought it important to impeach Milstead, Milstead’s attorney would not let Boyd’s counsel speak with him before trial, and Levinson did not talk to any of Milstead’s family or neighbors. Nor did Levinson consult with an independent pathologist or with the State’s pathologist in preparation for trial. Levinson offered that he was “possibly” in charge of the penalty hearing before the jury, and “guess[ed]” he did the preparation for it. Id. at 129. Levinson did not expect to have to start the penalty phase right after the guilt phase, but rather hoped to get an overnight continuance. In approaching the penalty phase, “there was an assumption that if there was a conviction, we would try to mitigate the effect of the conviction through a family member’s testimony; humanize the defendant, so to speak.” Id. at 132. Accordingly, Levinson asked Boyd’s sister Cindy to write a story about her brother, “essentially ask[ing] her to tell me some positive things about Glenn’s life as she grew up with him and as she knew him: to humanize him.” Id. at 131-32, 153-54. Levinson “[e]ssentially asked” Boyd’s mother “to do the same thing, give us something to let the jurors see what type of person Glenn is in terms of his positive aspects, his good side, his bright side.” Id. at 153-54. Levinson said that he met with Cindy and Boyd’s mother more than five times. He conceded that he would have welcomed evidence that Boyd grew up in a violent, abusive, or alcoholic home for a mitigation case, but that he did not investigate any of these possibilities. He also admitted that a penalty phase investigation might have been helpful. Cindy, Boyd’s sister, testified at the Rule 32 hearing that she met with Levinson about five times. Levinson asked Cindy about three months before trial to write a story about Boyd’s life, but she did not really know the purpose of writing the story. In a meeting some two days before trial, Levinson told Cindy that she would be called as a witness. Cindy said that Levinson met with her mother only on that one occasion. Cindy did not know what she would be testifying to until the day she testified, when Levinson called her into the hall and told her to read to the jury the account she had written. Cindy offered that the lawyers had not asked her about the violence, neglect, abuse, or alcoholism in their home, but that she would have been willing to testify about these issues. Levinson added that no one was in charge of the sentencing hearing before the judge that followed the jury’s verdict, and that they did not present additional evidence at that time because “[w]e stupidly thought that the judge would accept the jury’s recommendation.” Id. at 129-30, 145. Levinson also represented Boyd on appeal. He considered raising on appeal whether the State had presented false or misleading testimony through Milstead, but said that while he thought Milstead was a liar, he did not think the State “had anything to do with that,” since he did not “think the state would have knowingly put on perjured testimony.” Id. at 137. E. Potential Mitigating Evidence Boyd presented several witnesses at the state habeas hearing to testify about further mitigating evidence that could have been introduced at his original trial. Jan Vogelsang, a clinical social worker with some fifteen years of expertise in victimization and child trauma, testified about the “psychosocial assessment” she performed on Boyd. Vol. 17 at 171. Her summary of the various risk factors apparent in Boyd’s life included the following. First, Boyd’s father, Butch, was an alcoholic who was in and out of jail throughout Boyd’s childhood, humiliated his children and failed to support them, attacked his aging parents, and when he would return to the house unannounced and raging, he would destroy its contents. Second, Boyd’s stepfather, Don Oliver, who married Boyd’s mother when Boyd was eight, was a brutal man who beat the children. He regularly assaulted Boyd’s mentally disabled sister, Susie, and would lock her in her room for days and weeks. Oliver’s beatings of Boyd’s sister Cindy ultimately led social services to remove her from the home. On one occasion Oliver struck Boyd with his fists when Boyd sought to intervene in defense of his sister Susie, beat him another time when Boyd tried to protect his mother, and frequently hit Boyd on the head with a rifle butt when they went hunting. However, Oliver’s violence toward Boyd was not documented in any social service agency records. In addition, Dr. Karl Kirkland, the psychologist testifying on behalf of the State, said that Boyd had told him that Oliver hit him on the head with a rifle butt on one occasion. Third, Boyd’s mother loved her children but was unable either to provide for or to protect them, and attempted suicide when Boyd was eleven. Rats and snakes crawled in and out of the children’s belongings; when there was insufficient food, Boyd and his siblings sought nutrients from dirt, and also received food from their grandparents. Several of the social service records did say, however, that the children appeared to be well cared for and supervised, but these records also indicated that the Boyds frequently received governmental assistance. Fourth, Boyd’s alcoholic grandparents, at whose house Boyd spent significant amounts of time, beat each other in front of the children, who were “used to seeing them crawl in the house drunk on their knees.” Id. at 194, 196. Their drunkenness led them to jeopardize the children’s safety, as when they forced then-twelve-year-old Cindy to drive the family home from Florida to Alabama with six-year-old Boyd beside her. Finally, Boyd’s sister Cindy, who attempted to parent him, was only a child herself, and at some point, tried to kill herself. Cindy left when Boyd was nine years old and Oliver cut off her contact with Boyd, who was “basically left to more or less figure out life for himself.” Id. at 182, 212-13. Based on these circumstances, Vogelsang claimed that Boyd’s upbringing represented one of the worst family situations she had seen in terms of violence, neglect, and alcoholism. Vogelsang concluded that Boyd presented a high risk of being impulsive, had become emotionally constricted, and could not make sound decisions based on what he knew. On cross-examination, Vogelsang admitted that she had not considered the following positive factors, which were also present in Boyd’s life: (1) Boyd had very close relationships with his mother, his paternal grandparents, his sister, and his sister’s husband; (2) Boyd and Julie Greenwood had a romantic relationship in which they discussed marriage; and (3) Boyd’s great uncle, when Boyd was fifteen or sixteen years old, allowed Boyd to come live with him in New Mexico in order to teach Boyd how to become a mechanic. Cindy Pierce, Boyd’s sister, also testified at the Rule 32 hearing about Boyd’s deprived family background, conveying both more and in greater detail than she did at trial about the abuse and neglect the children had endured. Cindy confirmed that: (1) their grandparents were alcoholics who “fought” with each other, Vol. 17 at 11-14; (2) their father was rarely around, but when he was, he was “crazy,” would come in and destroy the furniture, would knock or slap down their mother, and occasionally beat his parents, id. at 23-26, 28; and (3) their stepfather was very cruel, treated their mother like a slave, beat her severely twice, beat sister Susie at least three times a week, and while he “wasn’t as quick and easy to beat [Boyd] as he was myself and [Susie],” probably beat Boyd about once a week. Id. at 29-33. Despite growing up in the same household as Boyd, Cindy did not commit any crimes, and at the time she testified, worked as a training supervisor at a manufacturing company. She explained that Boyd moved in with her at some point when he was approximately fourteen years old but that her efforts to discipline him were not well received. She also said that Boyd did not take advantage of the opportunity offered by their great uncle. At the Rule 32 hearing, Calhoun County Sheriff Roy Snead singled out Boyd’s father as suffering from serious alcoholism; he added that the father had been arrested twenty-six times. Retired Anniston police officer Bill Whatley also offered an episode of Oliver’s domestic abuse. Childhood neighbor Kathy Gurley, familiar with the stepfather’s physical and verbal assaults on Boyd and the mother’s helplessness, testified that violence was endemic throughout Boyd’s neighborhood. Gurley opined that Boyd was among the kindest of the youngsters she knew and believed his involvement in these offenses was wholly out of character. Boyd also relied upon the testimony of Dr. Louis Tetlow, a clinical psychologist for the Louisiana Department of Corrections. Dr. Tetlow performed a number of tests on Boyd and concluded that Boyd, among other things, had trouble planning ahead, was short-sighted and impulsive, unable to evaluate possible consequences or trust others, expressed emotional constriction, indicating an inability to be empathetic, had an abiding problem with authority, and evinced anger and rage. Dr. Tetlow further opined that Boyd had been adversely affected by his father’s absence, and by the beatings he sustained at his stepfather’s hand while his mother sat by passively. Dr. Tetlow concluded, however, that Boyd had above-average intelligence, no delusional beliefs, no signs of organic brain damage, and no history of alcohol or drug abuse. Dr. Tetlow agreed with Dr. Krichev’s pre-trial evaluation that Boyd did not meet the criteria for a psychological diagnosis and “really d[id] not have a major mental disorder.” Vol. 19 at 446. Dr. Karl Kirkland, a licensed psychologist certified by the State as a forensic examiner, testified on behalf of the State at the Rule 32 hearing. Dr. Kirkland described what he had heard during Boyd’s post-conviction hearing as “a pervasive history of emotional and physical abuse that has been very well documented.” Vol. 20 at 500-01. But, Dr. Kirkland opined, while Boyd had difficulty in expressing emotions, he was capable of recognizing-many emotions and expressing many of those feelings. Dr. Kirkland said that Boyd could easily form emotional attachments; he described the close relationships Boyd had with his sister Cindy, with his mother and grandparents, and with Cindy’s husband, and his fairly typical adolescent romantic relationship with Julie Greenwood. Dr. Kirkland agreed with the conclusions of Drs. Krichev and Tetlow that Boyd did not meet the criteria for any psychological diagnosis, and presented no mental health history, and no drug or alcohol history. Dr. Kirkland further observed that Boyd was of average intelligence, scoring high in comprehension and low in math, and that possible learning difficulties in math might have explained why he left school early. Dr. Kirkland also noted Boyd’s positive work history— including work in a fast-food restaurant as a dishwasher for a year, for a railroad company for a year, as an auto mechanic for three years, and as a television satellite technician for three to four months, rising to the level of a crew chief. Dr. Kirkland concluded that the abuse Boyd suffered in his childhood did not cause Boyd to commit murder. Regarding Boyd’s mental state at the time of the offense, Dr. Kirkland said that he could not find any evidence to suggest that Boyd was suffering from a mental illness at the time he committed the offenses or anything else that would reduce his criminal responsibility. Dr. Kirkland added that Boyd recognized the criminality of his conduct and was in complete control of his behavior at the time of the crime. F. Postr-Trial Procedural History 1. Boyd’s Direct Appeal Boyd appealed his conviction and sentence to the Alabama Court of Criminal Appeals. He was represented again by one of his trial lawyers, Levinson, and Michael Allsup, a lawyer appointed by the court for purposes of appeal. Three claims were made on direct appeal: (1) the warrantless search of Boyd’s impounded vehicle was unreasonable, and the evidence seized as a result of that search should have been deemed inadmissible; (2) the trial judge erred by refusing to answer the jury’s request that he define the distinction between “Murder and Capital Murder”; and (3) the Circuit Court lacked jurisdiction to try Boyd for Evelyn Blackmon’s murder. The Alabama Court of Criminal Appeals rejected each of Boyd’s claims, and affirmed Boyd’s conviction and death sentence. Boyd v. State, 542 So.2d 1247 (Ala. Cr.App.1988). Among other things, the court affirmed the trial judge’s decision to sentence Boyd to death, concluding that it had “found no evidence in th[e] record that the sentence was imposed under the influence of passion, prejudice, or any other arbitrary factor.” Id. at 1260. The appellate court independently re-weighed the aggravating and mitigating factors considered by the trial judge, a process which the court said “convinces us that death was the proper sentence to be imposed in this ease.” Id. The Alabama Court of Criminal Appeals added that Boyd’s sentence was not disproportionate to the penalties that had been imposed “in similar eases,” and that “[we] carefully searched this record for plain error and [we] have found none.” Id. Boyd petitioned the Supreme Court of Alabama for certiorari review; that court affirmed the decision of the Court of Criminal Appeals. Ex parte Boyd, 542 So.2d 1276 (Ala.1989). The United States Supreme Court denied certiorari. Boyd v. Alabama, 493 U.S. 883, 110 S.Ct. 219, 107 L.Ed.2d 172 (1989). 2. State Habeas Proceedings In July 1990, Boyd, represented by new counsel, filed a petition for post-conviction relief pursuant to Rule 20 of the Alabama Temporary Rules of Criminal Procedure, since renumbered as Rule 32. Boyd raised thirty-two claims in his Rule 32 petition, many with numerous sub-claims, including the suggestion that Boyd had received ineffective assistance of counsel both at trial and on direct appeal. The State responded, arguing that all of the claims, except those alleging ineffective assistance of counsel, were proeedurally barred. After the state habeas court summarily dismissed Boyd’s petition, Boyd moved for reconsideration of the dismissal of the petition, and on October 16, 1990, the trial court reinstated the petition. Boyd then filed an amended Rule 32 petition on July 8, 1994, raising thirty-seven claims, including thirty-one sub-claims involving ineffective assistance of counsel. On September 7, 1994, the Rule 32 trial judge entered an order of partial dismissal, dismissing all of Boyd’s claims except for those raising ineffective assistance of counsel, finding that the dismissed claims were foreclosed by Rule 32.2(a) and subject to summary dismissal pursuant to Ala. R.Crim. P. 32.7(b). Boyd’s Rule 32 petition primarily contended that his trial counsel had failed to investigate his background, or to conduct in-depth interviews with family members, or finally, to otherwise develop mitigating evidence for the sentencing phase. Beginning on September 8, 1994, and continuing on October 6, 1994, October 7, 1994, and October 12,1994, the state habeas court conducted an evidentiary hearing at which the parties submitted oral testimony, exhibits, and depositions. After receiving post-hearing briefs, the trial judge denied Boyd’s Rule 32 petition on July 25, 1997. The trial court explained its ruling this way: The Petitioner raises thirty (30) separate claims of ineffective assistance of counsel, both at the trial level and appellate level. Upon consideration of all of the above as it concerns and applies to each separate claim, this Court finds that the Petitioner has failed to show that his counsel’s representation, both at the trial level and appellate level, fell below the objective standard of reasonableness or that there was a reasonable probability that but for counsel’s unprofessional errors, if any, the outcome of his case would have been different, as required by Strickland v. Washington, 466 U.S. 668, 104 S.Ct. 2052, 80 L.Ed.2d 674 (1984). Vol. 5 at 944-45. Boyd appealed on September 4, 1997, raising numerous issues, including substantive claims alleging errors at trial and claims that his trial counsel and appellate counsel were ineffective. He also contended that the trial court erred in summarily dismissing claims that were properly presented in his Rule 32 petition. On December 18, 1998, the Alabama Court of Criminal Appeals affirmed the denial of relief. Boyd v. State, 744 So.2d 954 (Ala.Crim.App.1998) (Table). Following Boyd’s application for rehearing, the court withdrew the memorandum opinion and issued a published opinion on March 26, 1999, again affirming the denial of Boyd’s Rule 32 petition. Boyd v. State, 746 So.2d 364 (Ala.Crim.App.1999). The Alabama Court of Criminal Appeals described the evidence in support of Boyd’s penalty phase ineffectiveness claim: At the Rule 32 hearing, Boyd presented a wealth of testimony characterizing his childhood as consisting of continual gross poverty; gross physical and emotional abuse; gross neglect; and various humiliations. These indignities were bestowed at the hands of a cruel and alcoholic father and stepfather; a mentally disturbed mother; and loving but severely alcoholic grandparents. Id. at 377; see also id. at 377 n. 5 (noting the witnesses who testified regarding the ineffectiveness claim, among others). After recounting the testimony of the Rule 32 experts (Vogelsang and Dr. Tetlow for Boyd, and Dr. Kirkland for the State), the court concluded that each found that Boyd had made a “choice” to participate in the offense and that his horrific upbringing did not “cause” him to commit murder. Id. at mi. As for counsel’s performance at the penalty phase, the trial court characterized Levinson’s “assumption” that upon conviction counsel would “try to ... humanize the defendant, so to speak,” as a “tactical choice” that could not be second-guessed. Id. at 379. The court reiterated this conclusion when addressing counsel’s subsequent performance before the sentencing court. Additionally, it held that the Alabama statute “does not provide for the presentation of additional mitigation evidence at sentencing by the trial court,” and that trial counsel therefore did not err in failing to present any. Id. at 398. The Alabama Court of Criminal Appeals also noted that “Levinson’s penalty phase strategy was successful; the jury recommended, by a vote of 7-5, that Boyd be sentenced to life imprisonment without parole.” Id. at 379. The court further concluded that Boyd had failed to show that the lack of psychological evidence or any other evidence at the sentencing phase prejudiced him. It observed that “[i]n overruling the jury’s recommendation and sentencing Boyd to death, the trial court found that these crimes were ‘extremely wicked and shockingly evil[,’ and that] all Capital offenses are heinous atrocious and cruel to some extent, but the degree of heinousness and cruelty in these offenses far exceeds that which is common to all Capital offenses.” Id. (citing Boyd, 542 So.2d at 1268). The court determined that Boyd’s background was not a “factor” in the murders and that Boyd knew right from wrong, and thus concluded that the trial court would not have been persuaded to follow the jury’s recommendation even had this evidence been presented. Id. at 379. It said: We do not believe that this additional evidence would have shifted the balance between the aggravating circumstances and the mitigating circumstances and changed the outcome of the trial.... Had the testimony presented at the Rule 32 hearing regarding Boyd’s childhood been presented at the sentencing hearing it is highly unlikely that the trial court would have been persuaded to sentence Boyd differently. Id. The Alabama Court of Criminal Appeals also considered the merits of Boyd’s claim that counsel failed to effectively impeach Milstead. It held that expert assistance to challenge Milstead’s assertions “would [not] have changed the outcome of the trial.” Id. at 385-86. As for the sentencing impact of Milstead’s testimony, the court pointed to other evidence supporting the heinous, atrocious or cruel aggravating factor. Id. at 387. The court also determined that both the juror misconduct and the knowing-use-of-false-testimony claims had been defaulted. As for the former, it held that the trial court had “properly denied” the claim because it had not been pled pursuant to Ala. R.Crim. P. 32.1(e), which requires both proof of innocence and proof that the new facts would lead to a different result. Boyd, 746 So.2d at 405-07. It also ruled that the claim that the prosecution knew or should have known that it was introducing false testimony was presented differently in the trial court than on appeal. Id. at 409. The court also denied this claim on the ground that it too should have been pled pursuant to Rule 32.1(e). Id. Boyd sought certiorari review on all of his claims, but the Alabama Supreme Court denied certiorari without opinion. Ex parte Boyd, No. 1981080 (Ala. Oct. 22, 1999). 3. Federal Habeas Proceedings On October 16, 2000, Boyd commenced this federal petition for a writ of habeas corpus pursuant to 28 U.S.C. § 2254, in the United States District Court for the Northern District of Alabama, raising thirty-four claims. After receiving extensive briefing from both sides, the district court filed a 192-page memorandum opinion denying Boyd’s habeas petition in all respects. See D. Ct. Docket Entry (“Doc.”) 40 (filed Dec. 7, 2004). Notably, the district court denied Boyd’s claim of ineffective assistance of counsel during the penalty phase, on the ground that it “agree[d] with the conclusion of the Alabama Court of Criminal Appeals, that Boyd cannot satisfy the [Strickland ] ... prejudice prong, which focuses on whether the sentencer would have concluded that the balance of aggravating and mitigating circumstances did not warrant death.” Doc. 40 at 69 (quotation, punctuation, and citations omitted). The court reached this conclusion based on its assessment that Boyd’s argument as to prejudice rested on “a speculative foray into conceivable, but imponderable, outcomes.” Id. On December 22, 2004, Boyd moved the district court to alter or amend the judgment, pursuant to Fed.R.Civ.P. 59(e). Almost three years later, the district court granted in part and denied in part Boyd’s Rule 59(e) motion. Doc. 48. Specifically, based on “additional attention” to United States Supreme Court precedent, including the intervening decision of Rompilla v. Beard, 545 U.S. 374, 125 S.Ct. 2456, 162 L.Ed.2d 360 (2005), as well as “[cjareful consideration” of the arguments contained in Boyd’s Rule 59(e) motion, the district court granted Boyd relief on his claim that trial counsel was ineffective at the penalty phase, and ordered a remand “to the state trial court with instructions to assess the mitigating evidence that Boyd’s attorneys attempted to present at the Rule 32 hearing, and thereafter to conduct a proper, constitutional, evaluation of all mitigating factors adduced at trial and at the Rule 32 hearing, in their entirety, before re-weighing all of such evidence against the aggravating factors found in Boyd’s case.” Doc. 48 at 59 (emphasis omitted). The State filed a timely appeal concerning that portion of the district court’s order granting relief on the penalty phase ineffectiveness claim. On June 16, 2009, after the district court denied the State’s motion to stay the judgment pending the State’s appeal, this Court entered a stay. Order, Boyd v. Allen, No. 07-14908 (11th Cir. June 16, 2009). Boyd also filed a notice of appeal to this Court on a number of the issues rejected by the district court. Boyd moved for a certificate of appealability, which the district court granted concerning the following issues: I. Whether the extraneous evidence uttered in the jury room by alternate juror Edward Williams entitled Boyd to a full hearing and habeas relief; II. Whether Boyd was denied effective assistance of counsel during the guilt phase of trial, and; III. Whether the state courts’ disposition of Boyd’s claim that his co-defendant presented false testimony on the ground of a procedural default was an “adequate” basis upon which to preclude federal review of the claim. Doc. 55 at 4 (footnotes omitted). II. Standard of Review Because Boyd filed his federal habeas petition after April 24, 1996, Section 2254(d) governs this proceeding. Wilcox v. Florida Dep’t of Corr., 158 F.3d 1209, 1210 (11th Cir.1998). Accordingly, a federal court may grant habeas relief only where the state court decision was (1) “contrary to, or involved an unreasonable application of, clearly established Federal law, as determined by the Supreme Court of the United States”; or (2) “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). A state court’s factual findings are presumed correct unless rebutted by the petitioner with clear and convincing evidence. 28 U.S.C. § 2254(e)(1). A state court decision is “contrary to” clearly established law if the court arrived at a conclusion opposite to one reached by the Supreme Court on a question of law, or if the state court confronted facts that are “materially indistinguishable” from relevant Supreme Court precedent but arrived at a different result. Williams v. Taylor, 529 U.S. 362, 405, 120 S.Ct. 1495, 146 L.Ed.2d 389 (2000). A state court decision is an “unreasonable application” of clearly established law if the state court unreasonably extends or fails to extend a clearly established legal principle to a new context. Id. at 407, 120 S.Ct. 1495. An application of federal law cannot be considered unreasonable merely because it is incorrect or erroneous; rather, a state court decision also must be unreasonable. Id. at 410-11, 120 S.Ct. 1495. The district court’s resolution of questions of law and mixed questions of law and fact is reviewed de novo, as is the district court’s conclusion concerning the reasonableness of the state court’s application of federal law. LeCroy v. Sec’y, Fla. Dep’t of Corr., 421 F.3d 1237, 1259 (11th Cir.2005). III. Ineffective Assistance of Counsel During the Penalty Phase Boyd’s central claim is that he received ineffective assistance of counsel during the penalty phase of his trial because his counsel failed to adequately investigate and present mitigating evidence to the sentencing jury and the trial judge. To succeed on an ineffective-assistance-of-counsel claim, Boyd must show that: (1) “counsel’s representation fell below an objective standard of reasonableness,” and (2) “there is a reasonable probability that, but for counsel’s unprofessional errors, the result of the proceeding would have been different.” Strickland, 466 U.S. at 688, 694, 104 S.Ct. 2052; accord Knowles v. Mirzayance, — U.S.-, 129 S.Ct. 1411, 1420, 1422, 173 L.Ed.2d 251 (2009); Wiggins v. Smith, 539 U.S. 510, 521-22, 123 S.Ct. 2527, 156 L.Ed.2d 471 (2003); Williams v. Taylor, 529 U.S. 362, 390, 120 S.Ct. 1495, 146 L.Ed.2d 389 (2000); Darden v. Wainwright, 477 U.S. 168, 184, 106 S.Ct. 2464, 91 L.Ed.2d 144 (1986). Notably, a court “may decline to reach the performance prong of the ineffective assistance test if convinced that the prejudice prong cannot be satisfied.” Waters v. Thomas, 46 F.3d 1506, 1510 (11th Cir.1995) (citing Strickland, 466 U.S. at 697, 104 S.Ct. 2052). 1. Strickland Performance As an initial matter, we will assume, for purposes of this appeal, that the state habeas court unreasonably applied Strickland by finding that Boyd’s counsel performed adequately in preparing for and presenting mitigating evidence at the penalty phase of trial. We ground this assumption on the fact that counsel hinged their preparation mainly on the undirected essay of one family member, without following up on or seeking any of the many available public records about Boyd and his family, which would have materially furthered Boyd’s approach at sentencing. As the record shows, before the penalty phase, Boyd’s sister Cindy prepared, at counsel’s request, a summary of Boyd’s life that indicated a variety of childhood challenges — including an absentee father, a disabled sister, an impoverished upbringing, school problems, difficulties with his mother’s remarriage, a close grandfather’s death, and alcoholic grandparents. However, counsel never dug deeper into any of these issues. Had counsel done so, either by asking family members or looking into social service records, relevant mitigating evidence — about the Boyd children’s destructive father, their violent stepfather, their ineffective mother, and the dangers their alcoholic grandparents exposed them to — would have come to light. Yet for no apparent reason, counsel simply failed to investigate. See Wiggins, 539 U.S. at 525, 123 S.Ct. 2527 (finding counsel’s failure to investigate mitigating evidence deficient where “counsel uncovered no evidence in them investigation to suggest that a mitigation case, in its own right, would have been counterproductive, or that further investigation would have been fruitless”). Evidence of abuse and other background details about Boyd would have supported the approach counsel took at sentencing— both to “humanize” Boyd, and to demonstrate that Boyd felt “remorse.” See id. at 526, 123. S.Ct. 2527 (criticizing counsel for them failure to introduce details of Wiggins’ history, when “counsel put on a halfhearted mitigation case”). Indeed, defense counsel Levinson expressly testified that he would have welcomed evidence for a mitigation case that Boyd grew up in a violent, abusive, or alcoholic home, but he did not investigate any of these issues. Also consonant with this lack of investigative follow-through, Boyd’s counsel failed to prepare for or present any evidence at the sentencing hearing before the trial judge that followed the jury’s verdict. According to Levinson, no one was in charge of this hearing: “[W]e didn’t put any evidence on at the sentencing hearing, if I remember correctly. The jury had recommended life without [parole].... I think we felt that the job was essentially done.” Vol. 16 at 129-30. Levinson said that counsel did not present additional evidence because “[w]e stupidly thought that the judge would accept the jury’s recommendation.” Id. at 145. On this record and under our case law, the performance of Boyd’s counsel likely was deficient. We need not, however, conclusively resolve this question, because as we determine below, Boyd has failed to satisfy Strickland’s, prejudice prong. See Windom v. Sec’y, Dep’t of Corr., 578 F.3d 1227, 1248 (11th Cir.2009) (“We need not determine whether counsel’s limited investigation into Windom’s background and mental health constituted deficient performance under the first prong of Strickland because we conclude that, even assuming counsel performed deficiently, Windom was not prejudiced thereby.”); Hall v. Head, 310 F.3d 683, 699 (11th Cir.2002) (“[Although there is evidence in the record to support the district court’s finding of deficient performance, we need not and do not ‘reach the performance prong of the ineffective assistance test [because we are] convinced that the prejudice prong cannot be satisfied.’ Indeed, in order for Hall to obtain habeas relief under Strickland, he must establish not only that counsel’s performance was deficient, but also that counsel’s errors ‘actually had an adverse effect on the defense.’ ” (quoting Strickland, 466 U.S. at 693, 104 S.Ct. 2052)). 2. Strickland Prejudice To show prejudice, it must be established that, but for counsel’s unprofessional performance, there is a reasonable probability the result of the proceeding would have been different. See Strickland, 466 U.S. at 694, 104 S.Ct. 2052.... “It is not enough for the [petitioner] to show the errors had some conceivable effect on the outcome of the proceeding ...,” because “[v]irtually every act or omission of counsel would meet that test.” Id. at 693 [104 S.Ct. 2052],... Nevertheless, a petitioner “need not show that counsel’s deficient conduct more likely than not altered the outcome in the case.” Id. at 693 [104 S.Ct. 2052],... Rather, where, as here, a petitioner challenges a death sentence, “the question is whether there is a reasonable probability that, absent the errors, the sentencer ... would have concluded that the balance of aggravating and mitigating circumstances did not warrant death.” Id. at 695 [104 S.Ct. 2052].... Putman v. Head, 268 F.3d 1223, 1248 (11th Cir.2001); see also Ferguson v. Sec’y for Dep't of Corr., 580 F.3d 1183, 1198-99 (11th Cir.2009) (noting that Strickland asks if a different result is “reasonably probable,” not if it is “possible”). Thus, “[i]n assessing prejudice, we reweigh the evidence in aggravation against the totality of available mitigating evidence.” Wiggins, 539 U.S. at 534, 123 S.Ct. 2527 (emphasis added). In so doing, we presume a reasonable sentencer. See Williams v. Allen, 542 F.3d 1326, 1342 (11th Cir.2008) (citing Strickland, 466 U.S. at 695, 104 S.Ct. 2052 (“[T]he idiosyncracies of the particular decisionmaker, such as unusual propensities toward harshness or leniency!,] ... are irrelevant to the prejudice inquiry.”)). We begin our analysis accepting Boyd’s claim — and the State’s concession — that the state habeas courts unreasonably applied Strickland by resting their conclusions on the purported absence of a “causal relationship” between Boyd’s mitigating evidence and the aggravating evidence in assessing prejudice. See Williams, 542 F.3d at 1343-44 (concluding that, based on the state habeas court’s statement that “[t]he evidence regarding Williams’ background was never found to have a causal relationship with Williams committing capital murder,” the court unreasonably applied Strickland by emphasizing “the absence of a ‘causal relationship’ between Williams’ mitigating evidence and the statutory aggravator”). As a result, in our analysis, we are obliged to weigh de novo the aggravating circumstances against the totality of mitigating evidence that Boyd introduced at his original sentencing hearing and in his post-conviction proceedings. See Panetti v. Quarterman, 551 U.S. 930, 953, 127 S.Ct. 2842, 168 L.Ed.2d 662 (2007) (“When a state court’s adjudication of a claim is dependent on an antecedent unreasonable application of federal law, the requirement set forth in § 2254(d)(1) is satisfied. A federal court must then resolve the claim without the deference AEDPA otherwise requires.”). After conducting this de novo review, however, we are constrained to conclude, as the Supreme Court did in Strickland, that “[g]iven the overwhelming aggravating factors, there is no reasonable probability that the omitted evidence would have changed the conclusion that the aggravating circumstances outweighed the mitigating circumstances and, hence, the sentence imposed.” 466 U.S. at 700, 104 S.Ct. 2052. Indeed, the aggravating circumstances in this case are especially powerful. After hearing the testimony surrounding this p