Intellectual Disability and the Death Penalty

Introduction to Intellectual Disability (formerly Mental Retardation)

Atkins v. Virginia: Summary of Supreme Court decision exempting those with "mental retardation" from death penalty

Hall v. Florida: Summary of Supreme Court decision finding Florida's standards for intellectual disability too rigid

Moore v. Texas: Summary of Supreme Court decision finding Texas' use of non-scientific factors in determining intellectual disability inconsistent with Supreme Court precedent and the Eighth Amendment

The Case of Warren Hill (Georgia)

Executions of Defendants with Intellectual Disability Since 1976, but prior to Atkins

Definitions of "mental retardation" (intellectual disability) by state

State Statutes exempting those with mental retardation from the death penalty:

Model Legislation: "Mental Retardation and the Death Penalty: A Guide to State Legislative Issues" - for states to comply with the Atkins ruling, with commentary by Professor James Ellis, Univ. of New Mexico Law School.

Sentence Reversals in Intellectual Disability Cases since Atkins

Additional Resources

News and Developments - Current Year
News and Developments - Previous Years

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Intellectual Disability, formerly referred to as "mental retardation,"** is characterized by "significant limitations both in intellectual functioning and in adaptive behavior, which covers many everyday social and practical skills.  This disability originates before the age of 18." (Source: The American Association for Intellectual and Developmental Disabilities, 2010). The U.S. Supreme Court ruled in Atkins v. Virginia (2002) that the execution of those with mental retardation (intellectual disability) is unconstitutional. (See below). This condition is different from mental illness.  See DPIC's page on Mental Illness for more information.

**Note: "Intellectual Disability" is now the preferred term for describing significant limitations in both intellectual functioning and adaptive behavior. However, many court decisions, laws, and other official documents were written using the prior designation of “mental retardation.”  The shift to the new terminology was given impetus when the American Association on Mental Retardation (AAMR) changed its name to the American Association on Intellectual and Developmental Disabilities (AAIDD) in 2007. AAIDD has taken the position that the meanings of the two terms are identical, “Mental retardation and intellectual disability are two names for the same thing. But intellectual disability is gaining currency as the preferred term.” DPIC will endeavor to use the term "intellectual disability," while recognizing the use of "mental retardation” in court decisions and other quoted materials.

Atkins v. Virginia

Atkins v. Virginia: The U.S. Supreme Court Declares the Execution of Persons with "Mental Retardation" Unconstitutional

On June 20, 2002, the Supreme Court issued a landmark ruling ending the execution of those with intellectual disability. In Atkins v. Virginia, the Court held that it is a violation of the Eighth Amendment ban on cruel unusual punishment to execute death row inmates with "mental retardation". The decision reflects the national consensus which has formed on this issue. (Associated Press, June 20, 2002). Read the opinion. See also, DPIC's Press Release.

In 1989, the U.S. Supreme Court had upheld (5-4) the constitutionality of executing those with intellectual disability in Penry v. Lynaugh (492 U.S. 302).  The Court said "mental retardation" should be a mitigating factor to be considered by the jury during sentencing. Writing for the majority, Justice Sandra Day O'Connor said that a "national consensus" had not developed against executing those with "mental retardation."

At the time, only two states, Maryland and Georgia, prohibited such executions. Between the Penry and Atkins decisions, 16 additional states enacted laws prohibiting the execution of the "mentally retarded." The federal death penalty statute also forbids such executions. Prior to Atkins v. Virginia, eighteen states plus the federal government did not allow the execution of those with "mental retardation": AZ, AR, CO, CT, FL, GA, IN, KS, KY, MD, MO, NE, NM, NY*, NC, SD, TN, WA, and U.S. (*except for murder by a prisoner) Read summaries of the states' criteria for establishing and defining "mental retardation".]

See also, Professor James Ellis's model legislation and explanation for states to comply with the Atkins ruling: "Mental Retardation and the Death Penalty: A Guide to State Legislative Issues." Mental health experts have pointed out that those with intellectual disability are characterized by suggestibility and their willingness to please can lead them to confess - sometimes falsely - to capital crimes. In 1989, the American Bar Association established a policy opposing the execution of those with "mental retardation." The ABA held that execution of such individuals is unacceptable in a civilized society, irrespective of their guilt or innocence. In 1997, the continued imposition of the death penalty on those with intellectual disability and on juveniles contributed to the ABA's call for a nationwide moratorium on the death penalty.

Hall v. Florida

On May 27, 2014, the U.S. Supreme Court held in Hall v. Florida that Florida's strict IQ cutoff for determining intellectual disability in capital cases is unconstitutional. The Court concluded, "Florida’s law contravenes our Nation’s commitment to dignity and its duty to teach human decency as the mark of a civilized world." In 2002, the Court banned the execution of people with "mental retardation," but allowed states leeway in selecting a process for determining who would qualify for that exemption. According to Florida's Supreme Court, defendants with an IQ even one point above 70 cannot be considered intellectually disabled, even though most states allow for a margin of error in such tests. The Supreme Court's ruling stated that Florida's strict rule "disregards established medical practice" and noted that the "vast majority of states" rejected such a narrow interpretation of IQ scores. The Court held that, "When a defendant's IQ test score falls within the test's acknowledged and inherent margin of error, the defendant must be able to present additional evidence of intellectual disability, including testimony regarding adaptive deficits." Hall will receive a new hearing on his intellectual disability claim.

Read the full ruling here.

See also, Professor James Ellis's research paper, "Hall v. Florida: The Supreme Court's Guidance in Implementing Atkins" (James W. Ellis, William & Mary Bill of Rights Journal, 2014)

Moore v. Texas

On March 28, 2017, the Supreme Court struck down Texas' standard for evaluating intellectual disability in death penalty cases, calling the state's approach to reviewing an individual's deficits in adaptive functioning an "outlier" that, "[b]y design and in operation, ... create[s] an unacceptable risk that persons with intellectual disability will be executed." The Court granted relief to Petitioner Bobby James Moore, holding that Texas' use of non-scientific factors to determine whether a person is ineligible for the death penalty because of intellectual disability is "irreconcilable" with the Court's precedent and with the Eighth Amendment. The Court said that although states have discretion in how they enforce the constitutional prohibition against applying the death penalty to persons who are intellectually disabled, that discretion is not “unfettered.” When determining whether someone is intellectually disabled, the Court rejected Texas' approach because it is not “informed by the medical community’s diagnostic framework.” Texas adopted criteria for determining intellectual disability that critics and mental health advocates say would merely perpetuate stereotypes and that had no basis in medical literature. For example, the fact-finder must consider whether people who knew the person during childhood, such as family, friends, teachers, employers, authorities, “th[ought] he was mentally retarded.” Other questions also included whether he formulated plans, whether his conduct responsive to external stimuli is rational and appropriate, whether he responds coherently and rationally in response to questions, and whether he could lie in his own or others’ interests. Some of the factors are based upon the characteristics of the fictional character Lennie Smalls from John Steinbeck’s novel, Of Mice and Men. The Supreme Court found that this was an unscientific "invention" of the Texas court that was "untied to any acknowledged source" and that it lacked support from "any authority, medical or judicial." 

Read the majority and dissenting opinions here.  

Additional Resources

Disparities in Determinations of Intellectual Disability

A recent law review article reported wide variations among states in exempting defendants with intellectual disability from the death penalty. Professor John Blume (l.) of Cornell Law School, along with three co-authors, analyzed claims filed under the Supreme Court's decision in Atkins v. Virginia (2002) against executing defendants with intellectual disability (formerly, "mental retardation"). Overall, from 2002 through 2013, only about 7.7% (371) of death row inmates or capital defendants have raised claims of intellectual disability. The total "success" rate for such claims was 55%. In North Carolina, the success rate was 82%, and in Mississippi 57%. However, in Georgia (where Warren Hill was recently executed), the success rate for those claiming this disability was only 11%, and in Florida, the success rate was zero. The authors found that states that significantly deviated from accepted clinical methods for determining intellectual disability, such as Florida, Alabama, Georgia, and Texas, had the lowest success rates. To preserve equal protection under the law, the authors recommended the Supreme Court strike down aberrant practices in isolated states, just as it struck down Florida's strict IQ cutoff.


The group of AAIDD experts responsible for defining the condition of intellectual disability to the world now explains the move away from the term “mental retardation” to the term intellectual disability in an article published in the April issue of the journal, Intellectual and Developmental Disabilities. “At the heart of this shift is the understanding that this term covers the same population of individuals who were diagnosed previously with mental retardation in number, kind, level, type, and duration of the disability and the need of people with this disability for individualized services and supports,” explain Robert Schalock et al. in “The Renaming of Mental Retardation: Understanding the Change to the Term Intellectual Disability.” The article cites the new definition for intellectual disability and the assumptions on which it is based, although the official 11th edition of the AAIDD definition Manual is expected to be published in the year 2009. (Posted April 11, 2007).

"Timing Of IQ Test Can Be A Life Or Death Matter." Science Daily Magazine, October 6, 2003 - Full text of a news release from Science Daily Magazine about the implications on death row inmates who are given IQ tests in years in which alterations to results are made to re-establish the mean score at 100.

"An Empirical Look at Atkins v. Virginia and Its Application in Capital Cases John H. Blume, Sheri Lynn Johnson and Christopher Seeds; Tennessee Law Review, Vol. 76:625; Spring 2009 - States: "We found 234 cases adjudicating the substance of Atkins claims, which implies that about seven percent of all death row inmates have filed Atkins claims. . . .Nearly forty percent of all defendants who allege mental retardation have, in fact, proved it." 

The report, Beyond Reason: The Death Penalty and Offenders with Mental Retardation, provides numerous examples of persons who have been sentenced to death despite their profound intellectual limitations. 

"The Penry Penalty: Capital Punishment and Offenders with Mental Retardation" by Emily Fabrycki Reed; Lanham: University Press of America (1993).

"The Criminal Justice System and Mental Retardation: Defendants and Victims" by Ronald W. Conley, Ruth Luckasson, and George N. Bouthilet; Baltimore:Paul H. Brookes Publishing Co. (1992).

Intellectual Competence & the Death Penalty (Blog)

See also Mental Illness.

 Last Updated May 23, 2017