Atkins v. Virginia

536 U.S. 304, 122 S. Ct. 2242, 153 L. Ed. 2d 335, 2002 U.S. LEXIS 4648

Opinions

Justice Stevens

delivered the opinion of the Court.

Those mentally retarded persons who meet the law’s requirements for criminal responsibility should be tried and punished when they commit crimes. Because of their disabilities in areas of reasoning, judgment, and control of their impulses, however, they do not act with the level of moral culpability that characterizes the most serious adult criminal conduct. Moreover, their impairments can jeopardize the reliability and fairness of capital proceedings against mentally retarded defendants. Presumably for these reasons, in the 13 years since we decided Penry v. Lynaugh, 492 U. S. 302 (1989), the American public, legislators, scholars, and judges have deliberated over the question whether the death penalty should ever be imposed on a mentally retarded criminal. The consensus reflected in those deliberations informs our answer to the question presented by this case: whether such executions are “cruel and unusual punishments” prohibited by the Eighth Amendment to the Federal Constitution.

I

Petitioner, Daryl Renard Atkins, was convicted of abduction, armed robbery, and capital murder, and sentenced to death. At approximately midnight on August 16, 1996, Atkins and William Jones, armed with a semiautomatic handgun, abducted Eric Nesbitt, robbed him of the money on his person, drove him to an automated teller machine in his pickup truck where cameras recorded their withdrawal of additional cash, then took him to an isolated location where he was shot eight times and killed.

Jones and Atkins both testified in the guilt phase of Atkins’ trial.¹ Each confirmed most of the details in the other’s account of the incident, with the important exception that each stated that the other had actually shot and killed Nesbitt. Jones’ testimony, which was both more coherent and credible than Atkins’, was obviously credited by the jury and was sufficient to establish Atkins’ guilt.² At the penalty phase of the trial, the State introduced victim impact evidence and proved two aggravating circumstances: future dangerousness and “vileness of the offense.” To prove future dangerousness, the State relied on Atkins’ prior felony convictions as well as the testimony of four victims of earlier robberies and assaults. To prove the second aggravator, the prosecution relied upon the trial record, including pictures of the deceased’s body and the autopsy report.

In the penalty phase, the defense relied on one witness, Dr. Evan Nelson, a forensic psychologist who had evaluated Atkins before trial and concluded that he was “mildly mentally retarded.”³ His conclusion was based on interviews with people who knew Atkins,⁴ a review of school and court records, and the administration of a standard intelligence test which indicated that Atkins had a full scale IQ of 59.⁵

The jury sentenced Atkins to death, but the Virginia Supreme Court ordered a second sentencing hearing because the trial court had used a misleading verdict form. 257 Va. 160, 510 S. E. 2d 445 (1999). At the resentencing, Dr. Nelson again testified. The State presented an expert rebuttal witness, Dr. Stanton Samenow, who expressed the opinion that Atkins was not mentally retarded, but rather was of “average intelligence, at least,” and diagnosable as having antisocial personality disorder.⁶ App. 476. The jury again sentenced Atkins to death.

The Supreme Court of Virginia affirmed the imposition of the death penalty. 260 Va. 375, 385, 534 S. E. 2d 312, 318 (2000). Atkins did not argue before the Virginia Supreme Court that his sentence was disproportionate to penalties imposed for similar crimes in Virginia, but he did contend “that he is mentally retarded and thus cannot be sentenced to death.” Id., at 386, 534 S. E. 2d, at 318. The majority of the state court rejected this contention, relying on our holding in Penry. 260 Va., at 387, 534 S. E. 2d, at 319. The court was “not willing to commute Atkins’ sentence of death to life imprisonment merely because of his IQ score.” Id., at 390, 534 S. E. 2d, at 321.

Justice Hassell and Justice Koontz dissented. They rejected Dr. Samenow’s opinion that Atkins possesses average intelligence as “incredulous as a matter of law,” and concluded that “the imposition of the sentence of death upon a criminal defendant who has the mental age of a child between the ages of 9 and 12 is excessive.” Id., at 394, 395-396, 534 S. E. 2d, at 323-324. In their opinion, “it is indefensible to conclude that individuals who are mentally retarded are not to some degree less culpable for their criminal acts. By definition, such individuals have substantial limitations not shared by the general population. A moral and civilized society diminishes itself if its system of justice does not afford recognition and consideration of those limitations in a meaningful way.” Id., at 397, 534 S. E. 2d, at 325.

Because of the gravity of the concerns expressed by the dissenters, and in light of the dramatic shift in the state legislative landscape that has occurred in the past 13 years, we granted certiorari to revisit the issue that we first addressed in the Penry case. 533 U. S. 976 (2001).

II

The Eighth Amendment succinctly prohibits “[e]xcessive” sanctions. It provides: “Excessive bail shall not be required, nor excessive fines imposed, nor cruel and unusual punishments inflicted.” In Weems v. United States, 217 U. S. 349 (1910), we held that a punishment of 12 years jailed in irons at hard and painful labor for the crime of falsifying records was excessive. We explained “that it is a precept of justice that punishment for crime should be graduated and proportioned to [the] offense.” Id., at 367. We have repeatedly applied this proportionality precept in later cases interpreting the Eighth Amendment. See Harmelin v. Michigan, 501 U. S. 957, 997-998 (1991) (Kennedy, J., concurring in part and concurring in judgment); see also id., at 1009-1011 (White, J., dissenting).⁷ Thus, even though “imprisonment for ninety days is not, in the abstract, a punishment which is either cruel or unusual,” it may not be imposed as a penalty for “the ‘status’ of narcotic addiction,” Robinson v. California, 370 U. S. 660, 666-667 (1962), because such a sanction would be excessive. As Justice Stewart explained in Robinson: “Even one day in prison would be a cruel and unusual punishment for the ‘crime’ of having a common cold.” Id., at 667.

A claim that punishment is excessive is judged not by the standards that prevailed in 1685 when Lord Jeffreys presided over the “Bloody Assizes” or when the Bill of Rights was adopted, but rather by those that currently prevail. As Chief Justice Warren explained in his opinion in Trop v. Dulles, 356 U. S. 86 (1958): “The basic concept underlying the Eighth Amendment is nothing less than the dignity of man. . . . The Amendment must draw its meaning from the evolving standards of decency that mark the progress of a maturing society.” Id., at 100-101.

Proportionality review under those evolving standards should be informed by “ ‘objective factors to the maximum possible extent,’ ” see Harmelin, 501 U. S., at 1000 (quoting Rummel v. Estelle, 445 U. S. 263, 274-275 (1980)). We have pinpointed that the “clearest and most reliable objective evidence of contemporary values is the legislation enacted by the country’s legislatures.” Penry, 492 U. S., at 331. Relying in part on such legislative evidence, we have held that death is an impermissibly excessive punishment for the rape of an adult woman, Coker v. Georgia, 433 U. S. 584, 593-596 (1977), or for a defendant who neither took life, attempted to take life, nor intended to take life, Enmund v. Florida, 458 U. S. 782, 789-793 (1982). In Coker, we focused primarily on the then-recent legislation that had been enacted in response to our decision 10 years earlier in Furman v. Georgia, 408 U. S. 238 (1972) (per curiam), to support the conclusion that the “current judgment,” though “not wholly unanimous,” weighed very heavily on the side of rejecting capital punishment as a “suitable penalty for raping an adult woman.” Coker, 433 U. S., at 596. The “current legislative judgment” relevant to our decision in Enmund was less clear than in Coker but “nevertheless weigh[ed] on the side of rejecting capital punishment for the crime at issue.” Enmund, 458 U. S., at 793.

We also acknowledged in Coker that the objective evidence, though of great importance, did not “wholly determine” the controversy, “for the Constitution contemplates that in the end our own judgment will be brought to bear on the question of the acceptability of the death penalty under the Eighth Amendment.” 433 U. S., at 597. For example, in Enmund, we concluded by expressing our own judgment about the issue:

“For purposes of imposing the death penalty, Enmund’s criminal culpability must be limited to his participation in the robbery, and his punishment must be tailored to his personal responsibility and moral guilt. Putting Enmund to death to avenge two killings that he did not commit and had no intention of committing or causing does not measurably contribute to the retributive end of ensuring that the criminal gets his just deserts. This is the judgment of most of the legislatures that have recently addressed the matter, and we have no reason to disagree with that judgment for purposes of construing and applying the Eighth Amendment.” 458 U. S., at 801 (emphasis added).

Thus, in cases involving a consensus, our own judgment is “brought to bear,” Coker, 438 U. S., at 597, by asking whether there is reason to disagree with the judgment reached by the citizenry and its legislators.

Guided by our approach in these cases, we shall first review the judgment of legislatures that have addressed the suitability of imposing the death penalty on the mentally retarded and then consider reasons for agreeing or disagreeing with their judgment.

III

The parties have not called our attention to any state legislative consideration of the suitability of imposing the death penalty on mentally retarded offenders prior to. 1986. In that year, the public reaction to the execution of a mentally retarded murderer in Georgia⁸ apparently led to the enactment of the first state statute prohibiting such executions.⁹ In 1988, when Congress enacted legislation reinstating the federal death penalty, it expressly provided that a “sentence of death shall not be carried out upon a person who is mentally retarded.”¹⁰ In 1989, Maryland enacted a similar prohibition.¹¹ It was in that year that we decided Penry, and concluded that those two state enactments, “even when added to the 14 States that have rejected capital punishment completely, do not provide sufficient evidence at present of a national consensus.” 492 U. S., at 334.

Much has changed since then. Responding to the national attention received by the Bowden execution and our decision in Penry, state legislatures across the country began to address the issue. In 1990, Kentucky and Tennessee enacted statutes similar to those in Georgia and Maryland, as did New Mexico in 1991, and Arkansas, Colorado, Washington, Indiana, and Kansas in 1993 and 1994.¹² In 1995, when New York reinstated its death penalty, it emulated the Federal Government by expressly exempting the mentally retarded.¹³ Nebraska followed suit in 1998.¹⁴ There appear to have been no similar enactments during the next two years, but in 2000 and 2001 six more States — South Dakota, Arizona, Connecticut, Florida, Missouri, and North Carolina-joined the procession.¹⁵ The Texas Legislature unanimously adopted a similar bill,¹⁶ and bills have passed at least one house in other States, including Virginia and Nevada.¹⁷

It is not so much the number of these States that is significant, but the consistency of the direction of change.¹⁸ Given the well-known fact that anticrime legislation is far more popular than legislation providing protections for persons guilty of violent crime, the large number of States prohibiting the execution of mentally retarded persons (and the complete absence of States passing legislation reinstating the power to conduct such executions) provides powerful evidence that today our society views mentally retarded offenders as categorically less culpable than the average criminal. The evidence carries even greater force when it is noted that the legislatures that have addressed the issue have voted overwhelmingly in favor of the prohibition.¹⁹ Moreover, even in those States that allow the execution of mentally retarded offenders, the practice is uncommon. Some States, for example New Hampshire and New Jersey, continue to authorize executions, but none have been carried out in decades. Thus there is little need to pursue legislation barring the execution of the mentally retarded in those States. And it appears that even among those States that regularly execute offenders and that have no prohibition with regard to the mentally retarded, only five have executed offenders possessing a known IQ less than 70 since we decided Penry.²⁰ The practice, therefore, has become truly unusual, and it is fair to say that a national consensus has developed against it.²¹

To the extent there is serious disagreement about the execution of mentally retarded offenders, it is in determining which offenders are in fact retarded. In this case, for instance, the Commonwealth of Virginia disputes that Atkins suffers from mental retardation. Not all people who claim to be mentally retarded will be so impaired as to fall within the range of mentally retarded offenders about whom there is a national consensus. As was our approach in Ford v. Wainwright, 477 U. S. 899 (1986), with regard to insanity, “we leave to the State[s] the task of developing appropriate ways to enforce the constitutional restriction upon [their] execution of sentences.” Id., at 405, 416-417.²²

IV

This consensus unquestionably reflects widespread judgment about the relative culpability of mentally retarded offenders, and the relationship between mental retardation and the penological purposes served by the death penalty. Additionally, it suggests that some characteristics of mental retardation undermine the strength of the procedural protections that our capital jurisprudence steadfastly guards.

As discussed above, clinical definitions of mental retardation require not only subaverage intellectual functioning, but also significant limitations in adaptive skills such as communication, self-care, and self-direction that became manifest before age 18. Mentally retarded persons frequently know the difference between right and wrong and are competent to stand trial. Because of their impairments, however, by definition they have diminished capacities to understand and process information, to communicate, to abstract from mistakes and learn from experience, to engage in logical reasoning, to control impulses, and to understand the reactions of others.²³ There is no evidence that they are more likely to engage in criminal conduct than others, but there is abundant evidence that they often act on impulse rather than pursuant to a premeditated plan, and that in group settings they are followers rather than leaders.²⁴ Their deficiencies do not warrant an exemption from criminal sanctions, but they do diminish their personal culpability.

In light of these deficiencies, our death penalty jurisprudence provides two reasons consistent with the legislative consensus that the mentally retarded should be categorically excluded from execution. First, there is a serious question as to whether either justification that we have recognized as a basis for the death penalty applies to mentally retarded offenders. Gregg v. Georgia, 428 U. S. 153, 183 (1976) (joint opinion of Stewart, Powell, and Stevens, JJ.), identified “retribution and deterrence of capital crimes by prospective offenders” as the social purposes served by the death penalty. Unless the imposition of the death penalty on a mentally retarded person “measurably contributes to one or both of these goals, it ‘is nothing more than the purposeless and needless imposition of pain and suffering,’ and hence an unconstitutional punishment.” Enmund, 458 U. S., at 798.

With respect to retribution — the interest in seeing that the offender gets his “just deserts” — the severity of the appropriate punishment necessarily depends on the culpability of the offender. Since Gregg, our jurisprudence has consistently confined the imposition of the death penalty to a narrow category of the most serious crimes. For example, in Godfrey v. Georgia, 446 U. S. 420 (1980), we set aside a death sentence because the petitioner’s crimes did not reflect “a consciousness materially more ‘depraved’ than that of any person guilty of murder.” Id., at 433. If the culpability of the average murderer is insufficient to justify the most extreme sanction available to the State, the lesser culpability of the mentally retarded offender surely does not merit that form of retribution. Thus, pursuant to our narrowing jurisprudence, which seeks to ensure that only the most deserving of execution are put to death, an exclusion for the mentally retarded is appropriate.

With respect to deterrence — the interest in preventing capital crimes by prospective offenders — “it seems likely that ‘capital punishment can serve as a deterrent only when murder is the result of premeditation and deliberation,’ ” Enmund, 458 U. S., at 799. Exempting the mentally retarded from that punishment will not affect the “cold calculus that precedes the decision” of other potential murderers. Gregg, 428 U. S., at 186, Indeed, that sort of calculus is at the opposite end of the spectrum from behavior of mentally retarded offenders. The theory of deterrence in capital sentencing is predicated upon the notion that the increased severity of the punishment will inhibit criminal actors from carrying out murderous conduct. Yet it is the same cognitive and behavioral impairments that make these defendants less morally culpable — for example, the diminished ability to understand and process information, to learn from experience, to engage in logical reasoning, or to control impulses — that also make it less likely that they can process the information of the possibility of execution as a penalty and, as a result, control their conduct based upon that information. Nor will exempting the mentally retarded from execution lessen the deterrent effect of the death penalty with respect to offenders who are not mentally retarded. Such individuals are unprotected by the exemption and will continue to face the threat of execution. Thus, executing the mentally retarded will not measurably further the goal of deterrence.

The reduced capacity of mentally retarded offenders provides a second justification for a categorical rule making such offenders ineligible for the death penalty. The risk “that the death penalty will be imposed in spite of factors which may call for a less severe penalty,” Lockett v. Ohio, 438 U. S. 586, 605 (1978), is enhanced, not only by the possibility of false confessions,²⁵ but also by the lesser ability of mentally retarded defendants to make a persuasive showing of mitigation in the face of prosecutorial evidence of one or more aggravating factors. Mentally retarded defendants may be less able to give meaningful assistance to their counsel and are typically poor witnesses, and their demeanor may create an unwarranted impression of lack of remorse for their crimes. As Penry demonstrated, moreover, reliance on mental retardation as a mitigating factor can be a two-edged sword that may enhance the likelihood that the aggravating factor of future dangerousness will be found by the jury. 492 U. S., at 323-325. Mentally retarded defendants in the aggregate face a special risk of wrongful execution.

Our independent evaluation of the issue reveals no reason to disagree with the judgment of “the legislatures that have recently addressed the matter” and concluded that death is not a suitable punishment for a mentally retarded criminal. We are not persuaded that the execution of mentally retarded criminals will measurably advance the deterrent or the retributive purpose of the death penalty. Construing and applying the Eighth Amendment in the light of our “evolving standards of decency,” we therefore conclude that such punishment is excessive and that the Constitution “places a substantive restriction on the State’s power to take the life” of a mentally retarded offender. Ford, 477 U. S., at 405.

The judgment of the Virginia Supreme Court is reversed, and the case is remanded for further proceedings not inconsistent with this opinion.

It is so ordered.

1 Initially, both Jones and Atkins were indicted for capital murder. The prosecution ultimately permitted Jones to plead guilty to first-degree murder in exchange for his testimony against Atkins. As a result of the plea, Jones became ineligible to receive the death penalty.

2 Highly damaging to the credibility of Atkins’ testimony was its substantial inconsistency with the statement he gave to the police upon his arrest. Jones, in contrast, had declined to make an initial statement to the authorities.

3 The American Association on Mental Retardation (AAMR) defines mental retardation as follows: “Mental retardation refers to substantial limitations in present functioning. It is characterized by significantly subaverage intellectual functioning, existing concurrently with related limitations in two or more of the following applicable adaptive skill areas: communication, self-care, home living, social skills, community use, self-direction, health and safety, functional academics, leisure, and work. Mental retardation manifests before age 18.” Mental Retardation: Definition, Classification, and Systems of Supports 5 (9th ed. 1992).

The American Psychiatric Association’s definition is similar: “The essential feature of Mental Retardation is significantly subaverage general intellectual functioning (Criterion A) that is accompanied by significant limitations in adaptive functioning in at least two of the following skill areas: communication, self-care, home living, social/interpersonal skills, use of community resources, self-direction, functional academic skills, work, leisure, health, and safety (Criterion B). The onset must occur before age 18 years (Criterion C). Mental Retardation has many different etiologies and may be seen as a final common pathway of various pathological processes that affect the functioning of the central nervous system.” Diagnostic and Statistical Manual of Mental Disorders 41 (4th ed. 2000). “Mild” mental retardation is typically used to describe people with an IQ level of 50-55 to approximately 70. Id., at 42-43.

4 The doctor interviewed Atkins, members of his family, and deputies at the jail where he had been incarcerated for the preceding 18 months. Dr. Nelson also reviewed the statements that Atkins had given to the police and the investigative reports concerning this case.

5 Dr. Nelson administered the Weehsler Adult Intelligence Scales test (WAIS-III), the standard instrument in the United States for assessing intellectual functioning. AAMR, Mental Retardation, supra. The WAIS-III is scored by adding together the number of points earned on different subtests, and using a mathematical formula to convert this raw score into a scaled score. The test measures an intelligence range from 45 to 155. The mean score of the test is 100, which means that a person receiving a score of 100 is considered to have an average level of cognitive functioning. A. Kaufman & E. Liehtenberger, Essentials of WAIS-III Assessment 60 (1999). It is estimated that between 1 and 3 percent of the population has an IQ between 70 and 75 or lower, which is typically considered the cutoff IQ score for the intellectual function prong of the mental retardation definition. 2 Kaplan & Sadock’s Comprehensive Textbook of Psychiatry 2952 (B. Sadock & V. Sadock eds. 7th ed. 2000).

At the sentencing phase, Dr. Nelson testified: “[Atkins’] full scale IQ is 59. Compared to the population at large, that means less than one percentile. . . . Mental retardation is a relatively rare thing. It’s about one percent of the population.” App. 274. According to Dr. Nelson, Atkins’ IQ score “would automatically qualify for Social Security disability income.” Id., at 280. Dr. Nelson also indicated that of the over 40 capital defendants that he had evaluated, Atkins was only the second individual who met the criteria for mental retardation. Id., at 310. He testified that, in his opinion, Atkins’ limited intellect had been a consistent feature throughout his life, and that his IQ score of 59 is not an “aberration, malingered result, or invalid test score.” Id., at 308.

6 Dr. Samenow’s testimony was based upon two interviews with Atkins, a review of his school records, and interviews with correctional staff. He did not administer an intelligence test, but did ask Atkins questions taken from the 1972 version of the Weehsler Memory Scale. Id:, at 524-525, 529. Dr. Samenow attributed Atkins’ “academic performance [that was] by and large terrible” to the fact that he “is a person who chose to pay attention sometimes, not to pay attention others, and did poorly because he did not want to do what he was required to do.” Id., at 480-481.

7 Thus, we have read the text of the Amendment to prohibit ail excessive punishments, as well as cruel and unusual punishments that may or may not be excessive.

8 Jerome Bowden, who was identified as having mental retardation when he was 14 years old, was scheduled for imminent execution in Georgia in June 1986. The Georgia Board of Pardons and Paroles granted a stay following public protests over his execution. A psychologist selected by the State evaluated Bowden and determined that he had an IQ of 65, which is consistent with mental retardation. Nevertheless, the board lifted the stay and Bowden was executed the following day. The board concluded that Bowden understood the nature of his crime and his punishment and therefore that execution, despite his mental deficiencies, was permissible. See Montgomery, Bowden’s Execution Stirs Protest, Atlanta Journal, Oct. 13,1986, p. Al.

9 Ga. Code Ann. §17-7-131(j) (Supp. 1988).

10 The Anti-Drug Abuse Act of 1988, Pub. L. 100-690, §7001(0, 102 Stat. 4390, 21 U. S. C. § 848(0. Congress expanded the federal death penalty law in 1994. It again included a provision that prohibited any individual with mental retardation from being sentenced to death or executed. Federal Death Penalty Act of 1994,18 U. S. C. § 3596(c).

11 Md. Ann. Code, Art. 27, § 412(f)(1) (1989).

12 Ky. Rev. Stat. Ann. §§532.130, 532.135, 532.140; Term. Code Ann. §39-13-203; N. M. Stat. Ann. § 31-20A-2.1; Ark. Code Ann. §5-4-618; Colo. Rev. Stat. § 16-9-401; Wash. Rev. Code § 10.95.030; Ind. Code §§35-36-9-2 through 35-36-9-6; Kan. Stat. Ann. §21-4623.

13 N. Y. Crim. Proc. Law § 400.27. However, New York law provides that a sentence of death “may not be set aside . . . upon the ground that the defendant is mentally retarded” if “the killing occurred while the defendant was confined or under custody in a state correctional facility or local correctional institution.” N. Y. Crim. Proc. Law §400.27.12(d) (McKinney 2001-2002 Interim Pocket Part).

14 Neb. Rev. Stat. §28-105.01.

15 S. D. Codified Laws § 23A-27A-26.1; Ariz. Rev. Stat. Ann. § 13-703.02; Conn. Gen. Stat. §53a-46a; Fla. Stat. §921.137; Mo. Rev. Stat. §565.030; 2001-346 N. C. Sess. Laws p. 45.

16 House Bill No. 236 passed the Texas House on April 24, 2001, and the Senate version, S. 686, passed the Texas Senate on May 16, 2001. Governor Perry vetoed the legislation on June 17, 2001. In his veto statement, the Texas Governor did not express dissatisfaction with the principle of categorically excluding the mentally retarded from the death penalty. In fact, he stated: “We do not execute mentally retarded murderers today.” See Veto Proclamation for H. B. No. 236. Instead, his motivation to veto the bill was based upon what he perceived as a procedural flaw: “My opposition to this legislation focuses on a serious legal flaw in the bill. House Bill No. 236 would create a system whereby the jury and judge are asked to make the same determination based on two different sets of facts. ... Also of grave concern is the fact that the provision that sets up this legally flawed process never received a public hearing during the legislative process.” Ibid.

17 Virginia Senate Bill No. 497 (2002); House Bill No. 957 (2002); see also Nevada Assembly Bill 353 (2001). Furthermore, a commission on capital punishment in Illinois has recently recommended that Illinois adopt a statute prohibiting the execution of mentally retarded offenders. Report of the Governor’s Commission on Capital Punishment 156 (Apr. 2002).

18 A comparison to Stanford v. Kentucky, 492 U. S. 361 (1989), in which we held that there was no national consensus prohibiting the execution of juvenile offenders over age 15, is telling. Although we decided Stanford on the same day as Penry, apparently only two state legislatures have raised the threshold age for imposition of the death penalty. Mont. Code Ann. §45-5-102 (1999); Ind. Code §35-50-2-3 (1998).

19 App. D to Brief for AAMR et al. as Amici Curiae.

20 Those States are Alabama, Texas, Louisiana, South Carolina, and Virginia. D. Keyes, W. Edwards, & R. Perske, People with Mental Retardation are Dying Legally, 35 Mental Retardation (Feb. 1997) (updated by Death Penalty Information Center, available at http://www.advocacyone.org/deathpenalty.html (as visited June 18, 2002)).

21 Additional evidence makes it clear that this legislative judgment reflects a much broader social and professional consensus. For example, several organizations with germane expertise have adopted official positions opposing the imposition of the death penalty upon a mentally retarded offender. See Brief for American Psychological Association et al. as Amici Curiae; Brief for AAMR et al. as Amici Curiae. In addition, representatives of widely diverse religious communities in the United States, reflecting Christian, Jewish, Muslim, and Buddhist traditions, have filed an amicus curiae brief explaining that even though their views about the death penalty differ, they all “share a conviction that the execution of persons with mental retardation cannot be morally justified.” Brief for United States Catholic Conference et al. as Amici Curiae 2. Moreover, within the world community, the imposition of the death penalty for crimes committed by mentally retarded offenders is overwhelmingly disapproved. Brief for European Union as Amicus Curiae 4. Finally, polling data shows a widespread consensus among Americans, even those who support the death penalty, that executing the mentally retarded is wrong. Bonner & Rimer, Executing the Mentally Retarded Even as Laws Begin to Shift, N. Y. Times, Aug. 7, 2000, p. Al; App. B to Brief for AAMR et al. as Amici Curiae (appending approximately 20 state and national polls on the issue). Although these factors are by no means dis-positive, their consistency with the legislative evidence lends further support to our conclusion that there is a consensus among those who have addressed the issue. See Thompson v. Oklahoma, 487 U. S. 815, 830, 831, n. 31 (1988) (considering the views of “respected professional organizations, by other nations that share our Anglo-American heritage, and by the leading members of the Western European community”).

22 The statutory definitions of mental retardation are not identical, but generally conform to the clinical definitions set forth in n. 3, supra.

23 J. McGee & F. Menolascino, The Evaluation of Defendants with Mental Retardation in the Criminal Justice System, in The Criminal Justice System and Mental Retardation 55, 58-60 (R. Conley, R. Luckasson, & G. Bouthilet eds. 1992); Appelbaum & Appelbaum, Criminal-Justice Related Competencies in Defendants with Mental Retardation, 14 J. of Psychiatry & L. 483, 487-489 (Winter 1994).

24 See, e. g., Ellis & Luckasson, Mentally Retarded Criminal Defendants, 53 Geo. Wash. L. Rev. 414, 429 (1985); Levy-Shiff, Kedem, & Sevillia, Ego Identity in Mentally Retarded Adolescents, 94 Am. J. Mental Retardation 541, 547 (1990); Whitman, Self Regulation and Mental Retardation, 94 Am. J. Mental Retardation 347, 360 (1990); Everington & Fulero, Competence to Confess: Measuring Understanding and Suggestibility of Defendants with Mental Retardation, 37 Mental Retardation 212, 212-213, 535 (1999) (hereinafter Everington & Fulero).

25 See Everington & Fulero 212-213. Despite the heavy burden that the prosecution must shoulder in capital cases, we cannot ignore the fact that in recent years a disturbing number of inmates on death row have been exonerated. These exonerations have included at least one mentally retarded person who unwittingly confessed to a crime that he did not commit. See Baker, Death-Row Inmate Gets Clemency; Agreement Ends Day of Suspense, Washington Post, Jan. 15,1994, p. Al.