Full opinion text
B.D. PARKER, JR., Circuit Judge: Donald Fell was convicted of murdering Teresca King in the course of a carjacking and kidnapping. Following a hearing on possible penalties and a verdict rendered by the jury, he was sentenced to death by the United States District Court for the District of Vermont (Sessions, /.). In this appeal, Fell challenges his sentence on a number of grounds falling roughly into four categories: errors in jury selection, errors in the admission of certain evidence, prejudicial comments by the prosecutors, and the violation of certain provisions of the Federal Death Penalty Act (FDPA), 18 U.S.C. § 3591 et seq. We affirm. BACKGROUND This case stems from the brutal murders by Fell and his accomplice Robert Lee in November 2000 of Fell’s mother Debra, her companion Charles Conway, and King. The facts are largely undisputed. Fell, who was 20 years old at the time of the murders, does not contest his guilt and the government does not contest much of the evidence of the troubled childhood and adolescence that Fell adduced in an effort to avoid the death penalty. Fell spent his early years in Pennsylvania with parents who were chronic alcoholics. Both Fell and his sister were raped by babysitters when they were young children, abandoned by their parents, and raised by relatives. Fell had frequent brushes with the law of increasing seriousness and, for a period of time, was committed to a home for delinquent youth. After his release, his involvement with the law continued to escalate and was punctuated by serious drug and alcohol abuse. Fell’s mother moved to Rutland, Vermont in the fall of 1996 and Fell joined her in 2000. Their stormy relationship continued. Fell and his mother (and their friends) drank heavily, argued frequently, and abused drugs. For example, in November 2000, in an incident that was the subject of disputed trial testimony, Fell assaulted his mother in a bar. After taking his mother’s drink and attempting to rob her, Fell punched her in the head, knocked her to the ground and was arrested. On the evening of November 26, 2002, Fell, Lee, Debra Fell, and Charles Conway were playing cards at her residence. All were drinking heavily and some were using drugs. For reasons not reflected in the record, a violent altercation ensued. Fell produced a kitchen knife and stabbed Conway approximately 50 times causing his death. Lee began stabbing Debra Fell and killed her with multiple wounds to the head and neck. Fell and Lee then showered, took a shotgun that Fell had brought from Pennsylvania, and left on foot at approximately 3:30 am for a local mall in search of shells for the gun. Fell and Lee first went to Wal-Mart, but were turned away by a cleaning crew that informed them that the store was closed. Fell and Lee then approached a Price Chopper convenience store, where they found King, a 53 year old grandmother, just arriving for work in her car. Fell and Lee stole her car and forced her into the backseat at gunpoint. King attempted to escape while on the highway but Fell restrained her. After driving for several hours and entering New York state, Fell told King that she would be released. As they stopped the car to do so, Lee apparently had second thoughts and convinced Fell that they should kill her to prevent her from identifying them. The two forced King out of her car into the adjoining woods where they repeatedly kicked her and Lee struck her around the head and face with a rock. After killing her, Fell wiped his boots on her clothing. The two proceeded to Pennsylvania where they stole license plates, placed them on King’s car, and drove to Arkansas where they were arrested on November 30th. Following questioning by the Arkansas police and the FBI, Fell, verbally and in a written statement, confessed to the murder of Conway, described Debra Fell’s murder, and confessed to the murder of King. On December 2, he made a tape-recorded confession for Vermont police, who had flown to Arkansas. Subsequently, Fell and Lee were indicted. The four counts of the indictment charged them with (1) carjacking Teresca King with death resulting; (2) kidnapping and transporting Teresca King in interstate commerce with death resulting; (3) possession of a firearm in furtherance of a crime of violence; and (4) transporting a firearm in interstate commerce by fugitives. See 18 U.S.C. §§ 2119(2) & (3); 1201(a)(1) & (2); 924(c)(l)(A)(ii) & (2); 922(g)(2). Counts 1 and 2 were capital offenses. Before he could be tried, Lee died in prison in the fall of 2001 by his own hand in an accidental hanging. In October 2001, after extensive negotiations with the United States Attorney’s Office of Vermont, Fell signed a draft plea agreement that would have resolved the capital charges with a sentence of life without parole. The draft agreement stated that the government agreed to forego the capital charges “due to substantial mitigating evidence that has been uncovered related to the defendant’s mental health and impaired capacity at the time of the events; his mental health history and background; his assistance to authorities in locating Teresca King’s body; the fact that he was 20 years old when he murdered Teresca King and the fact that he does not have a substantial prior criminal history.” The draft agreement also provided that “this agreement will not become effective until approved by the Attorney General of the United States or his delegate, and until thereafter signed by the United States Attorney for the District of Vermont.” The draft was signed by Fell and his counsel, but was rejected by the Attorney General upon the advice of the standing committee of the Department of Justice that reviews death-eligible prosecutions. Cf. United States v. Sampson, 486 F.3d 13, 24 & n. 3 (1st Cir.2007) (describing these procedures); United States v. Wilk, 452 F.3d 1208, 1211 n. 2 (11th Cir.2006). The United States Attorney then agreed that, with the consent of the District Court, Fell would plead guilty in exchange for a bench trial on sentencing. The Attorney General rejected this agreement as well. In January 2002, the government filed a Notice of Intent to Seek the Death Penalty. See 18 U.S.C. § 3593(a). The notice stated that the government intended to prove four threshold culpability factors, id. § 3591(a), three statutory aggravating factors, id. § 3592(c), and four non-statutory aggravating factors, id. § 3593(a). After the Supreme Court’s decision in Ring v. Arizona, 536 U.S. 584, 122 S.Ct. 2428, 153 L.Ed.2d 556 (2002), called into question the validity of indictments in which the government did not charge statutory aggravating factors, the government obtained a superseding indictment which included the threshold culpability factors and the statutory aggravating factors. Fell, represented by the Federal Public Defender for the Northern District of New York, moved to dismiss the indictment on a number of grounds. He contended that the FDPA was unconstitutional because it permitted imposition of the death penalty on the basis of evidence that had not been tested according to the Sixth Amendment’s guarantee of confrontation or the Fifth Amendment’s guarantee of due process, or that would have been deemed inadmissible under the Federal Rules of Evidence. Id. at 489. The district court granted the motion. See United States v. Fell, 217 F.Supp.2d 469, 491 (D.Vt.2002). The government appealed and we reversed. See United States v. Fell, 360 F.3d 135 (2d Cir.2004) (“Fell I”), cert. denied, 543 U.S. 946, 125 S.Ct. 369, 160 L.Ed.2d 259 (2004). We held that the Constitution did not require adherence to the Federal Rules of Evidence. We also found the FDPA’s evidentiary provisions constitutional because they were consistent with the heightened reliability standards required in capital trials. Fell, 360 F.3d at 143-44. On remand, the district court rejected Fell’s remaining constitutional challenges. See Fell, 372 F.Supp.2d at 755 (D.Vt.2005). Jury selection began on May 4, 2005 and was completed on June 6. The guilt phase began on June 20 and ended on June 24. The government presented eighteen witnesses; the defense presented no evidence. The jury was charged on June 24 and, later that day, found Fell guilty on all counts. The penalty phase commenced on June 28. The government offered evidence from seven witnesses, including five victim impact witnesses, who attested to the devastating effects of King’s murder on her family and friends. The defense introduced testimony from fourteen witnesses, including Fell’s family members, teachers, social service providers, and correctional institution officials. These witnesses testified regarding Fell’s troubled childhood, his personal characteristics, the familial violence he witnessed and experienced, his early drug and alcohol abuse, and his adaptation to prison. The government then presented five rebuttal witnesses—three prison officials, one of Fell’s former teachers, and a former friend—to dispute this picture. The jury was charged on July 13. It was instructed to consider whether the prosecution had met its burden of proof as to each of the capital counts and whether Fell had established his mitigating factors by a preponderance of the evidence. To impose the death penalty, the jury was required to find one or more of the threshold eligibility factors, at least one of the statutory aggravating factors, and the existence of any non-statutory aggravating factors. In weighing the relevant aggravating and mitigating factors to determine the appropriate punishment, the jury was instructed to assess both the direct and the circumstantial evidence presented at the guilt and sentencing phases of the trial. The next day, the jury unanimously found the existence of each of the four threshold factors, the three statutory aggravating factors, and the five non-statutory aggravating factors. The verdict form indicated that seventeen mitigating factors had been found by at least one juror, of which eight were found unanimously. Ten jurors added to the verdict form a mitigating factor that had not been presented to them: “[tjotal life experience, failure of the state of Pennsylvania social and mental health services to effectively intervene in [Fell’s] childhood abuse and to treat or address his early antisocial behavior.” After considering the court’s instructions to weigh the aggravating and mitigating factors, the jury decided unanimously that a death sentence should be imposed. Fell filed a motion for a judgment of acquittal and a new trial, contending that prosecutorial misconduct at the penalty phase required that his death sentence be changed to one of life imprisonment, or alternatively that he be afforded a new penalty trial. The district court denied these motions on April 24, 2006. United States v. Fell, 2006 U.S. Dist. LEXIS 24707 (D.Vt. Apr. 24, 2006). Following a sentencing hearing in which the district court heard statements from the victim and from Fell, it imposed the death penalty consistent with the jury’s recommendation. See 18 U.S.C. §§ 3593(e)-3594. This appeal followed. DISCUSSION Fell raises a number of issues each of which we must consider separately. 18 U.S.C. § 3595. Most of our discussion considers the district court’s exclusion of three jurors, its exclusion of the draft plea agreement, the admission of evidence of a religious nature, the government’s compliance with the court’s instruction regarding mental health experts, and several allegedly improper arguments made by the prosecution, as well as Fell’s challenges to the superseding indictment. Different standards of review apply to these issues. We review challenges to a juror’s excusal for abuse of discretion, inquiring whether the trial court’s findings are “fairly supported by the record.” Wainwright v. Witt, 469 U.S. 412, 434, 105 S.Ct. 844, 83 L.Ed.2d 841 (1985); see also United States v. Stewart, 433 F.3d 273, 304 (2d Cir.2006). We review a district court’s evidentiary rulings for abuse of discretion. United States v. Yousef, 327 F.3d 56, 156 (2d Cir.2003). Conclusions of law, including those involving constitutional questions, are reviewed de novo. Ramos v. Town of Vernon, 353 F.3d 171, 174 (2d Cir.2003). A defendant’s conviction may be vacated if prosecutorial misconduct caused substantial prejudice implicating the right to due process. United States v. Elias, 285 F.3d 183, 190-92 (2d Cir.2002). However, “remarks of the prosecutor in summation do not amount to a denial of due process unless they constitute egregious misconduct.” Id. at 190 (internal citations omitted). Nearly all the evidentiary issues Fell raises were not preserved at trial and were presented for the first time either in his motion for a new trial or on appeal. These issues are generally subject to plain error review. Relief is unavailable unless (1) there was error; (2) it was plain; and (3) it prejudicially affected substantial rights. See Jones v. United States, 527 U.S. 373, 389-90, 119 S.Ct. 2090, 144 L.Ed.2d 370 (1999). “Upon concluding that an error occurred which is plain and affects substantial rights ... an appellate court [must] exercise its discretion to correct such error only ‘if the error seriously affects the fairness, integrity, or public reputation of judicial proceedings.’ ” United States v. Gonzalez, 110 F.3d 936, 945—46 (2d Cir.1997) (quoting United States v. Olano, 507 U.S. 725, 732-34, 113 S.Ct. 1770, 123 L.Ed.2d 508 (1993)). I. Jury Selection The district court conducted a two-part voir dire of potential jurors. Each potential juror was initially required to complete an extensive questionnaire, which included questions about personal history, knowledge of the case, and opinions regarding the death penalty. The veniremen were also asked to locate their opinion on the death penalty on a scale of one to ten, with one being strongly opposed to, and ten being strongly in favor of, the death penalty. At the start of the voir dire, the court announced that it would permit counsel to ask prospective jurors questions about their ability to impose the death penalty as suggested by the facts of the ease, as long as the primary purpose of the questions was to ensure impartiality. The court prohibited counsel from posing “stake-out” questions that might require a juror to speculate or precommit as to how, given certain facts, that juror would react. See Fell, 372 F.Supp.2d at 770. Each potential juror was then questioned individually, rather than in an array, first by the court, which generally inquired into exposure to pre-trial publicity and views on the death penalty, and then by the parties. Fell contends that the district court improperly excused three qualified prospective jurors, numbers 64, 141 and 195, in violation of Witherspoon v. Illinois, 391 U.S. 510, 519, 88 S.Ct. 1770, 20 L..Ed.2d 776 (1968) and Wainwright v. Witt, 469 U.S. 412, 420-21, 105 S.Ct. 844, 83 L.Ed.2d 841 (1985). Prospective Juror 64, Fell argues, was excused based on her general disfavor of capital punishment. Prospective Jurors 141 and 195 were, Fell contends, excused for expressing reservations about applying the death penalty under specific factual circumstances not presented by this case, even though they affirmed that they could consider and impose a death sentence if warranted by the evidence. Under Witherspoon and its progeny, “not all [prospective jurors] who oppose the death penalty are subject to removal for cause in capital cases.” Lockhart v. McCree, 476 U.S. 162, 176, 106 S.Ct. 1758, 90 L.Ed.2d 137 (1986). Instead, “those who firmly believe that the death penalty is unjust may nevertheless serve as jurors in capital cases so long as they state clearly that they are willing to temporarily set aside their own beliefs in deference to the rule of law.” Id. In Witt, the Supreme Court explained that “the proper standard for determining when a prospective juror may be excluded for cause because of his or her views on capital punishment ... is whether the juror’s views would prevent or substantially impair the performance of his duties as a juror in accordance with his instructions and his oath.” 469 U.S. at 424, 105 S.Ct. 844 (internal quotation marks omitted); see also Uttecht v. Brown, — U.S. —, 127 S.Ct. 2218, 2224, 167 L.Ed.2d 1014 (2007). That impairment occurs when those views “create an obstacle” to a prospective juror’s impartial consideration of the law and the facts. Witt, 469 U.S. at 434, 105 S.Ct. 844. Erroneously excluding a prospective juror based on her view on the death penalty is reversible error, see Gray v. Mississippi, 481 U.S. 648, 668, 107 S.Ct. 2045, 95 L.Ed.2d 622 (1987), and we review challenges to a district court’s exclusion of a juror on that basis for abuse of discretion. United States v. Quinones, 511 F.3d 289, 304 (2d Cir.2007). To survive our review, “voir dire need not establish juror partiality with ‘unmistakable clarity.’ Rather, it must be sufficient to permit a trial judge to form ‘a definite impression that a prospective juror would be unable to faithfully and impartially apply the law.’ ” Quinones, 511 F.3d at 301 (quoting Witt, 469 U.S. at 424, 426, 105 S.Ct. 844). As the Supreme Court explained in Witt: Many veniremen simply cannot be asked enough questions to reach the point where their bias has been made “unmistakably clear”; these veniremen may not know how they will react when faced with imposing the death sentence, or may be unable to articulate, or may wish to hide their true feelings. Despite this lack of clarity in the printed record, however, there will be situations where the trial judge is left with the definite impression that a prospective juror would be unable to faithfully and impartially apply the law.... [TJhis is why deference must be paid to the trial judge who sees and hears the juror. 469 U.S. at 424-26, 105 S.Ct. 844 (footnote omitted). Accordingly, our review affords substantial deference to the judgment of the district court, as “the question [before us] is not whether a reviewing court might disagree with the trial court’s findings, but whether those findings are fairly supported by the record.” Id. at 434, 105 S.Ct. 844. This deference is particularly warranted in light of a district court’s dependence on its direct observations of demeanor and subjective assessments of credibility when conducting jury selection. Demeanor and credibility assessments are “peculiarly within a trial judge’s province” and are therefore “entitled to deference ... on direct review.” Id. at 428, 105 S.Ct. 844. As the Supreme Court has explained, “[d]eference to the trial court is appropriate because it is in a position to assess the demeanor of the venire, and of the individuals who compose it, a factor of critical importance in assessing the attitude and qualifications of potential jurors.” Uttecht, 127 S.Ct. at 2224; see also Qui-nones, 511 F.3d at 303. Such deference is due here where the district court noted that it “looked past prospective jurors’ literal answers and ... based rulings on the demeanor of the jurors.” Fell, 372 F.Supp.2d at 767. 1. Prospective Juror 64 Fell contends that Prospective Juror 64—who expressed strong opposition to the death penalty, and indicated that she would have difficulty voting for it regardless of the law—was improperly excused because she also stated that she could follow the court’s instructions and apply the law despite her strong reservations. While the exclusion of this prospective juror presents a closer call than that of the other contested prospective jurors, we conclude that the trial court did not abuse its discretion in excusing her. On her juror questionnaire, Juror 64 indicated that on a scale of one to ten, with one being strongly opposed to the death penalty and ten being strongly in favor, she was a one. She noted that she was “strongly opposed to the death penalty” and would “lean more generally to having someone be sentenced to life imprisonment without parole than to be sentenced to death.” She stated that she would not “say that someone deserved death just because it was premeditated,” but could consider a death sentence to be appropriate for individuals who commit “unforgivable type[s] of war crimes” like genocide or mass murder. During voir dire, Juror 64 affirmed that while it would be “difficult” for her to vote for a death sentence, she could consider and apply the death penalty “as part of [her] job of being on the jury” if the circumstances warranted. She elaborated: Well, I feel like, you know, the courts at this time ... or at least the way that the law is written, that it does allow for one of the outcomes to be a death sentence. And I guess as part of the process of that being allowed, that I could ... I could follow that process. The court then probed into Juror 64’s reservations about imposing the death penalty asking whether, despite those views, she could “be fair to the government as well as the defendant ... [and] impartially consider both options, [the] death penalty and life imprisonment.” Juror 64 responded in the affirmative, but qualified her response, somewhat ambiguously, by stating that “[she] never considered being in a position of making that kind of decision” and that she could not “say to [the court] that [she] absolutely and unequivocally do[es] not believe in the death sentence.” When pressed further by the court on whether she could impose the death penalty under circumstances where that penalty would be appropriate under the law, she responded equivocally that she “probably could, yes.” The government then asked a series of questions, culminating in whether Juror 64 could impose a death sentence if the government carried its burden. She responded: “In theory, I’m very opposed to the death penalty, but it’s part of the process of this government, and so I guess if I was sitting as a juror, that—and that was part of the process, and I had made that decision to do that, then, yes, I could make that decision” but then further explained: Well, I am just playing the question over that you asked me in terms of if I could do that, and, you know, again, I would much more lean towards someone being [sentenced to] life without parole, but I think that if ... I had to make that decision, that I could be able to make that decision, yes. Defense counsel asked Juror 64 whether she could honestly consider imposing the death penalty, and she responded, “Yes.” Before excusing Juror 64 from the courtroom, the court made a final inquiry: “[D]o you think that, based on your views, you might lean unfairly ... toward one side or the other? Or do you feel that you could put aside any views ... [and] be very impartial in your decision about whether the death penalty is appropriate or whether life imprisonment is appropriate?” In response, she stated, “I guess I would have to say that I would definitely lean more towards life imprisonment than I would towards the death sentence, yes.” After counsel for both sides declined the court’s invitation to ask follow-up questions, Juror 64 was excused from the courtroom, and the government then moved to exclude her for cause. The court granted the government’s motion, explaining that it could not rely on Juror 64’s pledge to follow the court’s instructions: 99 percent of the juror[s] would say that they can follow [the instructions of the court]. The question is whether somebody, in light of their own particular views, can be impartial and fair. And, I really wanted an honest response and I think I got an honest response at the very end.... I asked whether she could be fair, and her response was, “I would lean toward life imprisonment.” ... I appreciate that she said she could follow instructions but ... I think my responsibility ... is to make an analysis of whether somebody really could be fair and impartial— I think that in context, she could not be fair and impartial, and so that’s the Court’s ruling, and she is excused. Defense counsel objected to the exclusion. A prospective juror is not required to affirm that she would favor, or lean toward, the death penalty under any particular circumstances in order to serve. Even “those who firmly believe that the death penalty is unjust may nevertheless serve as jurors in capital cases,” as long as they are able to subjugate their own beliefs to the need to follow the court’s instructions. Lockhart v. McCree, 476 U.S. 162, 176, 106 S.Ct. 1758, 90 L.Ed.2d 137 (1986). Juror 64 averred that she could do just that. Her acknowledgment that imposing a sentence of death would be difficult “did not demonstrate that [she was] unwilling or unable to follow the law or obey [her] oaths,” but rather that she may be “more emotionally involved or view [her] task with greater seriousness and gravity.” Adams v. Texas, 448 U.S. 38, 49, 100 S.Ct. 2521, 65 L.Ed.2d 581 (1980); see also Witt, 469 U.S. at 420, 105 S.Ct. 844. However, the district court’s concern that, despite Juror 64’s averments to the contrary, she could not be fair and impartial in considering the death penalty is well-grounded in the record. As previously noted, on her questionnaire, she indicated the strongest available opposition to the death penalty. Throughout the district court’s painstaking and thoughtful voir dire, Juror 64 walked a fine line between her opposition to the death penalty and her willingness to follow the district court’s instructions. The record clearly demonstrates that the court endeavored mightily to explore Juror 64’s ability to impartially apply the law and afforded both parties ample opportunity to assist in this effort. Nevertheless, at the conclusion of voir dire, the court, having the benefit of personally questioning and observing Juror 64, was left to ponder her suitability. While Juror 64 strongly opposed the death penalty and was unprepared to conclude that a defendant deserved death simply because a murder was premeditated, she simultaneously claimed that she could impose the death penalty as part of her responsibilities as a juror in spite of her expressed reluctance to do so. Under these circumstances, the district court concluded that Juror 64’s views might substantially impair her duties as a juror and excused her. This conclusion fell well within the court’s broad discretion. Uttecht, 127 S.Ct. at 2230; Witt, 469 U.S. at 434, 105 S.Ct. 844; see also Sampson, 486 F.3d at 41 (A trial court’s decision to excuse a prospective juror for cause may be upheld even when the juror “indicated some degree of willingness to put aside personal biases”). As we have recently observed, a “blunt acknowledgment of bias may support removal without further inquiry, [but] the more ambiguous a prospective juror’s responses, the more useful demeanor, and thus oral inquiry, become in allowing a trial judge to identify partiality warranting removal for cause.” Quinones, 511 F.3d at 301-02. Here Juror 64 made no “blunt acknowledgment” of bias but, instead, repeatedly responded to the district court’s questioning with ambiguous and qualified answers, thus making her demeanor and oral responses central to the court’s qualification inquiry. Based on our review of the voir dire transcript, we, like the district court, are left with the “ ‘definite impression’ ” that Juror 64 “ ‘would be unable to faithfully and impartially apply the law.’ ” Id. at 301 (quoting Witt, 469 U.S. at 424, 426, 105 S.Ct. 844). 2. Prospective Juror 141 Fell argues that Prospective Juror 141 was improperly excused “because the trial court applied too technical a view of case-specific voir dire, ultimately disregarding how Juror 141’s views on the death penalty would apply to this case.” In his questionnaire, Juror 141 described himself as a four out of ten—ie., not strongly opposed or in favor of capital punishment. He indicated that a defendant’s state of mind was important in his determination as to whether he would consider the death penalty. In conformity with the court’s prior ruling on case-specific questioning, see Fell, 372 F.Supp.2d at 770, the government asked Juror 141 whether he could consider the death penalty in a case that “didn’t involve murder, but simply involved someone engaging in violence, knowing that the act created a grave risk of death—not premeditated murder.” Juror 141 responded “no” without qualification or elaboration. The government then asked whether he would consider the death penalty in a case where the defendant committed an act that “constituted a reckless disregard for human life [but] not first degree or premeditated murder.” Juror 141 again replied, unequivocally, “No.” Defense counsel objected to the government’s line of questioning. In response, the government argued that because reckless disregard for human life under 18 U.S.C. § 3591(a)(2)(D) was alleged in the indictment as a gatekeeping factor, the government had the right to pursue questions related to whether the juror could impose the death penalty absent evidence of intent. Defense counsel then complained that this approach constituted a “stake-out” to determine whether Juror 141 would impose the death penalty if Fell were found guilty of reckless disregard for human life rather than whether he could impose death in that situation. The district court disagreed, stating that, in conformity with its prior ruling on case-specific questioning, see Fell, 372 F.Supp.2d at 770, the government could ask questions relating to its theory that Fell could be sentenced to the death penalty for conduct demonstrating recklessness. The court noted that defense counsel would have the opportunity to rehabilitate the juror and allowed the government to proceed. In the course of the government’s continued questioning, Juror conreiterated that “I just ... I really feel that the person, in order to be convicted of a death penalty, needs to have known what they were doing, to realize the consequences of what they were doing.” Defense counsel then inquired into whether Juror 141 could infer intent from a description of the violence inflicted and vioresulting damage or injury.” Juror 141 indicted that he could. Juror 141 also expressed a willingness to weigh willingand mitigating factors, pursuant to the instructions of the court, when considering whether death should be imposed. After this exchange, the district court returned to the issue of whether Juror 141 would consider imposing the death imposfor a killing that was reckless but not intentional, describing the reckless acts as “kicking or stomping.” Juror 141 reversed course and claimed that he could consider imposing the death penalty on the basis of such violence, acknowledging that he ac“somewhat contradicting [himself].” Following a bench conference, the court found, over Fell’s objection, that the question of Juror 141’s qualification was “so close” that it would not be “fair to proceed with him” and excluded him for cause. The court provided no further reasoning and was not required to do so in light of its discretion in such matters. See United States v. Mitchell, 502 F.3d 931, 956 (9th Cir.2007); Sampson, 486 F.3d at 41. We see no error in the district court’s decision to exclude this prospective juror. Juror 141’s responses were not consistent or clear on whether he understood that the death penalty could be imposed for murder resulting from reckless disregard for human life and whether he would be able to apply it under such circumstances. A juror’s voir dire responses that are ambiguous or reveal considerable confusion may demonstrate substantial impairment. Uttecht, 127 S.Ct. at 2229 (“[A juror’s] assurances that he would consider imposing the death penalty and would follow the law do not overcome the reasonable inference from his other statements that in fact he would be substantially impaired in this case....”). The district court properly considered all of Juror 141’s responses in the context in which they were given and did not err in concluding that his views would significantly interfere with his duties as juror. See Witt, 469 U.S. at 434, 105 S.Ct. 844; Darden, 477 U.S. at 178, 106 S.Ct. 2464. We find no abuse of discretion. 3. Prospective Juror 195 Prospective Juror 195 rated herself as an eight on the ten-point scale of support for the death penalty contained in the juror questionnaire. Despite her support for the death penalty “[a]t a philosophical level,” she noted that she was unsure whether she “could vote in favor of it when the decision is in [her] hands.” In response to the court’s questions about whether she could impose the death penalty if the circumstances warranted, she repeatedly answered “I don’t know” or “more yes than no” and gauged her ability to do so as “60/40.” The district court’s decision to excuse Juror 195 turned on her inconsistent and generally negative responses when asked whether she would consider imposing the death penalty for a single murder. Juror 195 felt that the death penalty was “not appropriate for every murder” but would be justified “if it was a serial killer or mass murder, say on a mass shooting spree.” She also stated that she did not think she would vote in favor of the death penalty “for one killing.” The government moved to exclude her for cause following this exchange: The CouRt: The question is whether you could follow the instruction and consider the possible death penalty for one ... if there’s only one death. JuROR 195: Probably not. I would probably not be in favor of the death penalty in that scenario. Under the FDPA, a defendant is eligible for the death penalty if the jury finds the charged homicide, a statutory intent element or threshold mental culpability factor under § 3591(a)(2), and at least one of the statutory aggravating factors in § 3592(c). Although Fell was charged with three statutory aggravating factors—including committing multiple killings in a single criminal episode under § 3592(c)—two of the factors related to the death of King. In the event that the jury found that the killings were not part of a single criminal episode, Fell would still be eligible for the death penalty if the jury found at least one of the threshold mental culpability factors and that he had caused King’s death during the commission of a kidnapping or that he had committed the offense in an especially cruel or depraved manner. Therefore, the government argued that if Juror 195 could not consider imposing the death penalty without finding that Fell engaged in multiple killings, she would be substantially impaired in her ability to follow the law. Before ruling, the district court gave defense counsel the opportunity to question Juror 195. In response to defense questioning, she stated that she could consider the death penalty in “any case” and would listen to the facts presented to make that determination. Moments later, when questioned again by the government, Juror 195 retreated to her earlier position that, for the murder “of a single person, [she] would probably say no, I would not be able to choose the death penalty.” The court excused Juror 195 based on its assessment that “she would have difficulty following the instructions with regard to the single killing,” that she was ambiguous as to whether she could actually vote for the death penalty, and because the court “[could not] feel assured that she would be fair to the government’s side.” Despite numerous attempts by the court and government to point out that her position disqualified her from jury service, Juror 195 maintained that she would not consider the death penalty for a single killing while still claiming that she could fulfill her duties as a juror and follow the court’s instructions. Given Juror 195’s inconsistent positions, it is unlikely that she would have followed the court’s instructions if empaneled in this case. Accordingly, we conclude that the district court’s decision to excuse Juror 195 was proper. II. EXCLUSION OP THE DRAET Plea Agreement Fell assails the district court’s exclusion of a draft plea agreement on the ground that it was mitigation evidence that rebutted the government’s position that Fell had not accepted responsibility. See Green v. Georgia, 442 U.S. 95, 97, 99 S.Ct. 2150, 60 L.Ed.2d 738 (1979). Fell’s argument is driven by two contentions. First, he argues that the trial court misapplied the FDPA’s evidentiary standards governing the admission of evidence. Second, he claims that the exclusion of the agreement denied him an opportunity to rebut the government’s misrepresentations about his willingness to plead guilty and accept responsibility. We disagree. In 2001, the parties considered a plea agreement under which Fell would plead guilty to Count 2 of the original Indictment—kidnapping Teresca King with death resulting—in exchange for a sentence of life imprisonment. The proposed plea agreement detailed “substantial mitigating evidence” related to Fell’s “mental health and impaired capacity at the time of the events[;] ... his mental health history; his youth; his remorse; his assistance to authorities; and his lack of any substantial prior criminal history.” Id. at 782. Fell and his attorneys signed the agreement, but the prosecutors did not. Under Department of Justice guidelines, the proposed agreement was expressly conditioned on approval by the Attorney General, after which the U.S. Attorney for the District of Vermont could sign the agreement. The Attorney General rejected Fell’s agreement and the government filed notice that it would seek the death penalty. In a pre-trial submission, the government moved to bar admission of the draft agreement as well as information surrounding plea negotiations at the guilt and penalty phases of the trial. Fell, 372 F.Supp.2d at 781. The government characterized the plea agreement, a conditional offer that was subject to acceptance by the Attorney General, as containing the unen-dorsed opinion of the prosecution and embodying inchoate compromise negotiations barred by Federal Rules of Evidence 408 and 410. Fell agreed that the evidence was irrelevant at the guilt phase, but opposed the motion, claiming that the proposed agreement contained binding judicial admissions that substantial mitigating factors existed. He also contended that the Fifth and Eighth Amendments as well as § 3593(c) of the FDPA compelled admission of the draft. On May 26, 2005, the district court excluded the draft plea agreement—and statements made during plea negotiations—as irrelevant because “a prosecutor’s statements of personal belief regarding [aggravating and mitigation] factors should have no bearing on the jury’s independent evaluation of the evidence.” United States v. Fell, 372 F.Supp.2d 773, 783 (D.Vt.2005). The court also emphasized that the statements in the proposed plea agreement were never adopted by the government. See id. It concluded that while the draft’s probative value was negligible because “the opinions of the prosecutors [did not] make the existence or nonexistence of any mitigating factor more probable or less probable,” id., it could prejudicially distract the jury from making its own independent evaluation of the mitigating and aggravating factors. Finally, the court determined that public policy disfavored evidence that would deter plea bargaining. However, the district court permitted Fell to introduce during the penalty phase a stipulation that he had offered to plead guilty to Count 2 in exchange for a sentence of life imprisonment without parole. In the court’s view, Fell’s “offer [was] relevant to the mitigating factor of acceptance of responsibility.” Id. The stipulation informed the jury that “on May 18th, 2001, Donald Fell, through his attorneys and in writing, offered to plead guilty to Count II of the indictment, kidnapping, death resulting, in exchange for a life sentence without the possibility of release. The government refused that offer.” In summation, defense counsel contended that Fell’s attempt to plead guilty demonstrated that he had accepted responsibility, assisted law enforcement, and felt remorse. In response, the government argued in closing: Ladies and gentlemen, the judge instructed you. You know the law. Life imprisonment without the possibility of release is the minimum sentence that Donald Fell faces for kidnapping with death resulting. It’s the minimum sentence. When he offered to make that plea, he knew the evidence against him was overwhelming. He knew there was no doubt he was going to be convicted, so he asked for the minimum sentence. We rejected that, ladies and gentlemen. We wanted a jury to decide the appropriate sentence in this case. And, ladies and gentlemen, let’s take a look at the last part of this: He’s maintained that offer to this day. Ladies and gentlemen, we had to try and convict him. If he wanted to plead guilty, he could have pled guilty. We had a guilt phase in this case, ladies and gentlemen. We put on our case. We met our burden. We proved it. And now we are here to decide what is the just sentence. The minimum sentence? Or death sentence. Fell did not object or request a curative measure at the time. When he moved for a new trial, he argued that the government committed misconduct by taking inconsistent positions with respect to the facts underlying the stipulation. By minimizing Fell’s cooperation and acceptance of responsibility, he contended, the government took a position inconsistent with that which it had set forth in the draft plea agreement. This alleged misconduct, Fell urged, entitled him to be re-sentenced to life imprisonment or to receive a new sentencing hearing. The district court denied the motion. On appeal, Fell renews his objection to the court’s exclusion of the draft agreement and mounts an expanded challenge to the government’s allegedly improper rebuttal comments. As to the agreement, he argues that the court violated the FDPA because the draft agreement was relevant to the mitigation factors. He also makes a two-fold claim regarding the government’s misconduct. First, Fell believes that once the prosecution commented in its closing argument on his refusal to plead guilty, he should have been permitted to introduce the draft agreement as rebuttal evidence. Second, he avers that the government’s intimations about his refusal to plead guilty impermissibly burdened his right to plead not guilty. Since Fell failed to object to the prosecution’s comments, we review for plain error. While we see none with respect to the court’s exclusion of the draft agreement, the prosecutor’s remarks present a more complicated question. In cases governed by the FDPA, the Federal Rules of Evidence do not apply at the penalty phase. See 18 U.S.C. § 3593(c); Fell I, 360 F.3d at 143. The FDPA provides that information relevant to the sentence, including any mitigating or aggravating factor: is admissible regardless of its admissibility under the rules governing admission of evidence at criminal trials except that information may be excluded if its probative value is outweighed by the danger of creating unfair prejudice, confusing the issues, or misleading the jury.... The government and the defendant shall be permitted to rebut any information received at the hearing, and shall be given fair opportunity to present argument as to the adequacy of the information to establish the existence of any aggravating or mitigating factor, and as to the appropriateness in the case of imposing a sentence of death. 18 U.S.C. § 3593(c). See Fell I, 360 F.3d at 146 (upholding the constitutionality of this provision of FDPA and collecting cases so holding). Accordingly, a capital defendant has a right to introduce “as a mitigating factor, any aspect of a defendant’s character or record and any of the circumstances of the offense that the defendant proffers as a basis for a sentence less than death.” Lockett v. Ohio, 438 U.S. 586, 604, 98 S.Ct. 2954, 57 L.Ed.2d 973 (1978) (emphasis in original). The Supreme Court recognized, however, that its holding did not “limit[ ] the traditional authority of a court to exclude, as irrelevant, evidence not bearing on the defendant’s character, prior record, or the circumstances of his offense.” Id. at 604 n. 12, 98 S.Ct. 2954. Likewise, the FDPA’s evidentiary standards do “not mean that the defense has carte blanche to introduce any and all evidence that it wishes.” United States v. Purkey, 428 F.3d 738, 756 (8th Cir.2005). Nor does the FDPA “eliminate th[e] function of the judge as gatekeeper of constitutionally permissible evidence.” Fell I, 360 F.3d at 145. The court’s exclusion of the draft agreement was within its “traditional authority” to exclude evidence of questionable relevance. The district court appropriately concluded that, pursuant to 18 U.S.C. § 3593(c), the draft agreement’s inclusion of the unadopted statements of the prosecutors lacked evidentiary value and that it would distract the jury from an independent assessment of the mitigating factors. In addition, admission of the draft would authorize a confusing and unproductive inquiry into incomplete plea negotiations. See Berger v. United States, 295 U.S. at 88, 55 S.Ct. 629 (stating that the opinions of prosecutors should properly carry no weight with the jury); accord United States v. Melendez, 57 F.3d 238, 240-41 (2d Cir.1995). For these reasons, we see no error—much less abuse of discretion— in the district court’s decision to exclude the opinions of the prosecutors set forth in the draft plea agreement. Fell next argues that the prosecutor misrepresented his willingness to plead guilty by stating, in closing argument, that “if [Fell] wanted to plead guilty he could have.” Fell contends that, in order to correct this purported misrepresentation, he should have been allowed to introduce the draft agreement in rebuttal. Further, Fell maintains that the prosecution’s remark implicated his right to plead not guilty and avail himself of a jury trial. Because Fell did not preserve his challenge at trial, we review for plain error and conclude that the prosecution’s statement falls well short of meeting this test. First, the draft agreement did not need to be admitted in rebuttal to the prosecution’s statements. To the extent Fell sought to introduce the draft agreement to bolster his mitigation defense that he accepted responsibility and to counter the prosecution’s comments that he did not, the agreement was cumulative of the stipulation informing the jury that the government refused his offer to plead guilty. In any event, the record is virtually conclusive that the jury was clearly aware of Fell’s willingness to plead guilty. On the verdict form, all twelve jurors found that “Donald Fell offered to plead guilty to kidnapping and murdering Teresca King, knowing that the law requires a sentence of life in prison without the possibility of release, and he has maintained that offer to this day.” In addition, six jurors found the mitigating factors addressed in the agreement—concluding that Fell had “admitted responsibility for the death of Teresca King” and had “assisted law enforcement.” Regardless, all twelve jurors unanimously found that the government had established each of the alleged aggravating factors. In view of the jurors’ responses, even if the agreement had been admitted and an additional six jurors had found that Fell had admitted responsibility, the result of the penalty phase would not have been different. Fell’s constitutional objection to the government’s comments that as a consequence of his plea of not guilty, the government “had to try to convict him” and “if [Fell] wanted to plead guilty, he could have pled guilty” requires a different analysis. Fell contends that this argument constituted an improper attempt, in violation of the Fifth and Sixth Amendments, to defeat a mitigating factor and impermissibly penalize him for pleading not guilty. Fell first challenged these comments in his motion for a new trial only on the due process ground of the inconsistency between the prosecution’s original view that the existence of mitigating evidence warranted plea negotiations and its position during the penalty phase that any mitigating factors were far outweighed by the aggravating circumstances of the ease. Fell, 2006 U.S. Dist. LEXIS 24707, at *33. Since no mention was made of the Sixth Amendment below, we review his claim for plain error. We have held that, when addressing the jury, a prosecutor “must avoid commenting in a way that trenches on the defendant’s constitutional rights and privileges. For example, []he may not permissibly comment on the failure of the defendant to testify, or invite the jury to ‘presume’ in the absence of countervailing evidence that the government’s view of the case is correct, or suggest that the defendant has any burden of proof or any obligation to adduce any evidence whatever.” United States v. Parker, 903 F.2d 91, 98 (2d Cir.1990). In order to prevail on a claim of prosecutorial misconduct, a defendant must demonstrate “that the prosecutor’s remarks were improper and ... that the remarks, taken in the context of the entire trial resulted in substantial prejudice.” United States v. Bautista, 23 F.3d 726, 732 (2d Cir.1994). The challenged comments occurred in response to Fell’s endeavor to use the stipulation of his offer to plead guilty to prove acceptance of responsibility as a mitigating factor. In summation, the prosecution sought to place the stipulation in context by noting that, when faced with overwhelming evidence of his guilt, Fell offered to plead guilty in exchange for the minimum penalty authorized for his conduct. When this offer was not accepted, the government proceeded to a trial that Fell could have avoided by pleading unconditionally. At that trial, the government was put to a burden which it met. We believe these arguments—which the jury was repeatedly told were not evidence— were reasonable responses to Fell’s use of the stipulation. No error occurred. See Darden, 477 U.S. at 183, 106 S.Ct. 2464. III. PROseoutoR’s Statements Regarding Consideration of Mitigating Factors Fell next contends that he was denied a fair sentencing hearing because the prosecutor erroneously argued that the jury could not consider mitigating evidence that was unrelated to the crimes for which he had been found guilty. During summation, the prosecutor made the following arguments: [Y]ou should consider, one, [w]hat do these factors have to do with the crimes in this case? And do these factors actually lessen the defendant’s responsibility and culpability for these crimes? ... [E]ven if you find evidence of some of those mitigating factors, we submit to you that the weight of these factors is not that heavy, and you need not give them much, if any, weight based upon those two questions ... ... you have heard so much about the defendant’s childhood, so much about his background, and again, let me just remind you, the question is, we submit to you, what’s the connection between his background and childhood and these crimes? What about his background and childhood makes him less responsible, less culpable? What about them means that he should receive a less—a lesser sentence? The question is, what does that sexual assault when he was four or five have to do with the crimes in this case? Sixteen years later, there’s nothing sexual about these crimes. There’s nothing about that background and that history that shows you that he is less responsible for the decisions that he made, decisions like killing a witness. How does that have to do with what happened to him, which was terrible? What’s the evidence of the mitigating factors? To the extent you find some, there are not that many, respectfully, and they really don’t relate to the crimes. Fell maintains that these closing comments, by suggesting that the relevance of his mitigating evidence depended on its connection with his crimes of conviction, violated the constitutional and statutory rule that before imposing the death penalty, a jury must “be able to consider and give effect to a defendant’s mitigating evidence.... ” Penry v. Johnson, 532 U.S. 782, 797, 121 S.Ct. 1910, 150 L.Ed.2d 9 (2001) (requiring that a jury “be able to consider and give effect to a defendant’s mitigating evidence in imposing [its] sentence .... ”); accord Lockett, 438 U.S. at 604, 98 S.Ct. 2954. A capital defendant’s mitigating evidence need not have a nexus to the murder for which he has been convicted, but need only allow “the sentencer to reasonably find that it warrants a sentence less than death.” Tennard v. Dret-ke, 542 U.S. 274, 285, 124 S.Ct. 2562, 159 L.Ed.2d 384 (2004); FDPA § 3592(a)(8) (defining mitigating evidence as “factors in the defendant’s background, record, or character or any other circumstance of the offense that mitigate against imposition of the death sentence”); FDPA § 3593(c) (providing that “[a]t the sentencing hearing, information may be presented as to any matter relevant to the sentence, including any mitigating or aggravating factor permitted or required to be considered under section 3592”). Following the jury’s recommendation of a death sentence, Fell moved for a new trial based on his claim of improper statements by the government. The district court denied the motion, holding that—in the context of the entire proceeding and specifically, in light of its instructions to the jury—Fell had not been denied due process. Reviewing for plain error, we agree that there was no reasonable likelihood that the jurors believed themselves to be precluded from considering Fell’s mitigating evidence unless it related to his charged crimes. See Ayers v. Belmontes, 549 U.S. 7, 127 S.Ct. 469, 480, 166 L.Ed.2d 334 (2006); McKoy v. North Carolina, 494 U.S. 433, 442, 110 S.Ct. 1227, 108 L.Ed.2d 369 (1990). In its charge to the jury, the district court defined mitigating factors as those relating to Fell’s childhood and background and instructed the jury to consider all aggravating and mitigating factors in rendering its decision. Specifically, the court instructed that: [a] mitigating factor is not offered to justify or excuse a defendant’s conduct. A mitigating factor is simply an extenuating fact about a defendant’s life or character, or about the circumstances surrounding the murder, or anything else relevant that would suggest that a sentence of life in prison without the possibility of release is more appropriate punishment than a sentence of death. The court listed the mitigating factors that Fell had presented and told the jury that they could consider any additional mitigating factors that had not been specifically raised by Fell’s counsel. The court also instructed the jurors that the arguments of counsel were not evidence and that if any conflicted with the court’s instructions, the latter controlled. Specifically, the jurors were told that mitigating and aggravating factors “have to do with the circumstances of the crime, or the personal traits, character, or background of the defendant, or anything else relevant to the sentencing decision.” Moreover, the court’s instructions, as a whole, “made it clear that the jury was to take a broad view of mitigating evidence.” Ayers, 127 S.Ct. at 478. In light of these thorough instructions, as well as the amount of time and attention devoted to Fell’s early life experiences by both parties and the fact that the prosecutor’s comments formed a very brief part of his summation and were not repeated during his rebuttal, it is extremely unlikely that the jury felt constrained in its consideration of Fell’s mitigating evidence. See Boyde v. California, 494 U.S. 370, 384, 110 S.Ct. 1190, 108 L.Ed.2d 316 (1990) (“[A]r-guments of counsel generally carry less weight with a jury than do instructions from the court. The former are usually billed in advance to the jury as matters of argument, not evidence, and are likely viewed as the statements of advocates; the latter, we have often recognized, are viewed as definitive and binding statements of the law.” (internal citation omitted)); cf. Brown v. Payton, 544 U.S. 133, 146, 125 S.Ct. 1432, 161 L.Ed.2d 334 (2005) (“The judge is, after all, the one responsible for instructing the jury on the law, a responsibility that may not be abdicated to counsel.”). Indeed, the verdict form bears out this conclusion. The jury unanimously found eight background mitigating factors, including that Fell was sexually and physically abused as a child, that he was treated and institutionalized on several occasions due to mental health problems and that his parents were violent alcoholics who abandoned him. Significantly, ten individual jurors found additional mitigating factors not expressly provided by the defense: “total life experience, failure of the state[’s] ... social and mental health services to effectively intervene in his childhood abuse and to treat or address his early antisocial behavior.” No juror could have reached such conclusions while believing that to qualify as a mitigating factor, that factor need have a nexus to the crime. TV. Mental Health Evidenoe Fell next argues that the government committed misconduct by violating a district court order concerning mental health evaluations. During the course of plea negotiations in 2001, the defense provided a variety of mitigation information to the government, including the disclosure that it had hired experts to conduct mental health evaluations of Fell. After rejecting the proposed plea agreement and filing its notice of intent to seek the death penalty, the government moved for discovery of all mental health evidence and for Fell to submit to an examination by a government expert. Although the court never ruled on this motion, the defense voluntarily produced the reports and agreed to limited evaluations by two government experts, doctors Richard Wetzel and John Rabun. Fell, 372 F.Supp.2d at 758. The district court later observed that the limitations were appropriate because “in absence of Fed.R.Crim.P. 12.2(c), Fell’s statements could be used as evidence against him at trial.” Fell, 372 F.Supp.2d at 758. Drs. Wetzel and Rabun both produced reports based on their examinations of Fell. After we decided Fell I, in December 2004, the defense gave formal notice that it planned to introduce expert evidence on Fell’s mental condition. See Fed.R.CRIm.P. 12.2(b). Subsequent to that announcement, the government moved for a court-ordered examination of Fell’s mental health pursuant to Federal Rule of Criminal Procedure 12.2(c)(1)(B). The government then requested an unrestricted examination of Fell by a third expert, Dr. Michael Weiner, it had retained in early 2004. Specifically, the government sought to have Weiner question Fell regarding his state of mind at the time of the murders. Fell, 372 F.Supp.2d at 759. The series of events that followed is somewhat complicated. The defense objected to the need for a new examination and to the government’s use of a third expert for this purpose. On April 7, 2005, the district court ruled that the government should be allowed a further examination to assess Fell’s mental condition at the time of the offense. Id. at 779. However, because Rabun and Wetzel had already conducted extensive interviews exploring both mitigating and aggravating circumstances “at a time closer to the relevant events,” id. at 761, the court ruled that their opinions would satisfy Rule 12.2 “while at the same time not subjecting Fell to an extensive forensic interview by a new expert at this late stage in the proceeding,” id. at 762. The order accompanying the district court’s opinion provided that the examination “may be conducted by Dr. Rabun or Dr. Wetzel, or both,” and that the examiner would be permitted to conduct a complete psychiatric examination. The same order required that prior to any examination by an expert for the government, the government