News

What to Know: Intellectual Disability & the Death Penalty

By Hannah Weinstein

Posted on Apr 21, 2026 | Updated on Apr 21, 2026

DPI’s ​“What to Know” series exam­ines cap­i­tal pun­ish­ment from mul­ti­ple angles, one top­ic at a time. Each install­ment pro­vides essen­tial facts and data on spe­cif­ic aspects of the death penalty. 

Why it Matters: In 2002, the United States Supreme Court held that exe­cut­ing indi­vid­u­als with intel­lec­tu­al dis­abil­i­ty is uncon­sti­tu­tion­al. (Atkins v. Virgina). Before that deci­sion, dozens of peo­ple with intel­lec­tu­al dis­abil­i­ties were legal­ly exe­cut­ed. In Atkins, the Supreme Court explained that peo­ple with intel­lec­tu­al dis­abil­i­ty have dimin­ished per­son­al cul­pa­bil­i­ty due to their impair­ment and there­fore, impos­ing the most severe pun­ish­ment on them is dis­pro­por­tion­ate. Further, the Court high­light­ed that peo­ple with intel­lec­tu­al dis­abil­i­ty are at a high­er risk of wrong­ful exe­cu­tion: they are more like­ly to give false con­fes­sions; are less able to assist coun­sel; and have more dif­fi­cul­ty tes­ti­fy­ing on their own behalf, among oth­er rea­sons.1

  • Intellectual dis­abil­i­ty affects about 1% of the population. 
  • From 2002 to 2013, 7.7% of death row pris­on­ers or cap­i­tal defen­dants raised claims of intellectual disability. 

Key Facts: 

  • There are wide vari­a­tions among states in apply­ing Atkins and exempt­ing defen­dants with intel­lec­tu­al dis­abil­i­ty from the death penalty. 
  • Intellectual dis­abil­i­ty claims are fre­quent­ly denied on pro­ce­dur­al grounds rather than on the mer­its.2
  • International human rights law treats the exe­cu­tion of indi­vid­u­als with intel­lec­tu­al dis­abil­i­ty as a vio­la­tion of fundamental protections. 

Key Cases: 

Atkins set out three cri­te­ria for deter­min­ing intel­lec­tu­al dis­abil­i­ty: (1) sub­av­er­age intel­lec­tu­al func­tion­ing [typ­i­cal­ly mea­sured by IQ test­ing], (2) sig­nif­i­cant lim­i­ta­tions in adap­tive func­tion­ing, and (3) onset of these lim­i­ta­tions before the age of 18.3

The U.S. Supreme Court left the states with the task of imple­ment­ing these stan­dards, result­ing in vari­a­tion in how claims are eval­u­at­ed.4

Holding: A strict cut­off for IQ scores that pre­cludes oth­er con­sid­er­a­tions of intel­lec­tu­al dis­abil­i­ty in cap­i­tal cas­es is uncon­sti­tu­tion­al.5

Holding: State stan­dards for deter­min­ing whether a per­son is exempt from the death penal­ty because of intel­lec­tu­al dis­abil­i­ty must rely on cur­rent med­ical stan­dards defin­ing intel­lec­tu­al dis­abil­i­ty.6

Holding: (1) In deter­min­ing whether a per­son is intel­lec­tu­al­ly dis­abled, the med­ical com­mu­ni­ty [and there­fore the states must com­ply] focus­es the adap­tive-func­tion­ing inquiry on adap­tive deficits, not adap­tive strengths. (2) ​“Lay per­cep­tions” of intel­lec­tu­al dis­abil­i­ty and ​“lay stereo­types” may not be used to deter­mine intel­lec­tu­al dis­abil­i­ty.7

Joseph Clifton Smith, an Alabama death-row pris­on­er, argues that he is intel­lec­tu­al­ly dis­abled and there­fore inel­i­gi­ble for exe­cu­tion under Atkins. Mr. Smith had five full-scale IQ scores rang­ing from 72 to 78, and an Alabama fed­er­al dis­trict court vacat­ed his death sen­tence after con­clud­ing he has an intel­lec­tu­al dis­abil­i­ty.8 9 10

The Eleventh Circuit affirmed that relief in 2023, but the U.S. Supreme Court vacat­ed the deci­sion and remand­ed the case in November 2024, request­ing clar­i­fi­ca­tion of the Eleventh Circuit’s rea­son­ing. The Eleventh Circuit respond­ed that it had used a holis­tic approach eval­u­at­ing all the evi­dence, includ­ing all IQ scores, in reach­ing its deci­sion. The U.S. Supreme Court then grant­ed cer­tio­rari and sched­uled oral argu­ments for December 10, 2025. At issue is whether Alabama’s pro­ce­dures ade­quate­ly pro­tect peo­ple with intel­lec­tu­al dis­abil­i­ty from exe­cu­tion as the Constitution and the Court’s prece­dent require. A deci­sion is expect­ed by June 2026.11

Individual Profiles: 

Bobby Moore – Applying Atkins 

Bobby Moore

Bobby James Moore grew up in extreme pover­ty in Houston, strug­gling in school from an ear­ly age and often rely­ing on oth­ers to help him nav­i­gate every­day tasks. Teachers described him as unable to keep up with class­mates and func­tion­ing far below grade lev­el, reflect­ing life­long intel­lec­tu­al and adap­tive lim­i­ta­tions.12 After he was sen­tenced to death for the 1980 rob­bery-mur­der of James McCarble, Mr. Moore lat­er raised an intel­lec­tu­al dis­abil­i­ty claim under Atkins. Mr. Moore’s case led to two major deci­sions by the Supreme Court of the United States requir­ing courts to rely on cur­rent med­ical stan­dards when eval­u­at­ing intel­lec­tu­al dis­abil­i­ty. Mr. Moore was ulti­mate­ly rec­og­nized as a per­son with intel­lec­tu­al dis­abil­i­ty, and his death sen­tence was vacat­ed. He now serves a life sen­tence in Texas.13

Warren Lee Hill – Proving Intellectual Disability ​“Beyond a Reasonable Doubt”  

Warren Lee Hill

Warren Lee Hill grew up with seri­ous cog­ni­tive impair­ments dat­ing back to child­hood, reflect­ed in school records and accounts from teach­ers and fam­i­ly mem­bers.14 Mr. Hill was sen­tenced to death for the 1990 mur­der of fel­low pris­on­er Joseph Handspike while he was already serv­ing a life sen­tence for the fatal shoot­ing of his for­mer girl­friend, Myra Wright.15 After Atkins barred the exe­cu­tion of peo­ple with intel­lec­tu­al dis­abil­i­ty, Mr. Hill pur­sued an intel­lec­tu­al dis­abil­i­ty claim in state habeas pro­ceed­ings. At that hear­ing, Mr. Hill’s four experts said he met the cri­te­ria for intel­lec­tu­al dis­abil­i­ty, while the State’s three experts ini­tial­ly dis­agreed. Later, all three of the State’s experts changed their opin­ions — mean­ing every expert who had eval­u­at­ed Mr. Hill agreed that he was a per­son with intel­lec­tu­al dis­abil­i­ty.16 However, Georgia required Mr. Hill to prove his intel­lec­tu­al dis­abil­i­ty beyond a rea­son­able doubt, the high­est bur­den of proof in the legal sys­tem and the high­est of any state.17 Although a low­er court found Mr. Hill had an intel­lec­tu­al dis­abil­i­ty under a dif­fer­ent stan­dard, the Georgia Supreme Court lat­er reversed and rein­stat­ed his death sen­tence because he had not sat­is­fied Georgia’s ​“beyond a rea­son­able doubt” stan­dard.18 Mr. Hill was exe­cut­ed by Georgia in 2015, despite the unan­i­mous expert con­sen­sus that he was a per­son whom the United States Supreme Court said should not be exe­cut­ed.19 

Earl Washington – Hope & Exoneration

Earl Washington

Earl Washington Jr. was a farm work­er in rur­al Virginia who lived with sig­nif­i­cant intel­lec­tu­al lim­i­ta­tions and strug­gled with read­ing, com­pre­hen­sion, and com­mu­ni­ca­tion.20 His dis­abil­i­ty made him high­ly vul­ner­a­ble dur­ing police ques­tion­ing, where he was even­tu­al­ly coerced to sign a con­fes­sion to a mur­der he did not com­mit.21 Mr. Washington was erro­neous­ly sen­tenced to death for the mur­der of Rebecca Lynn Williams in 1984.22 Washington spent near­ly 18 years in prison, much of it on death row, before DNA test­ing proved his inno­cence.23 In 2000 he received a full par­don from Virginia Governor Jim Gilmore.24 He lat­er received a finan­cial set­tle­ment of approx­i­mate­ly $1.9 mil­lion after fil­ing a civ­il rights law­suit for his wrong­ful con­vic­tion and impris­on­ment.25 Mr. Washington’s case became one of the most promi­nent exam­ples of a wrong­ful con­vic­tion involv­ing an indi­vid­ual with intel­lec­tu­al dis­abil­i­ty, high­light­ing the height­ened risk of false con­fes­sions and wrong­ful exe­cu­tion in cap­i­tal cas­es.26 

Historical Perspective: 

  • For much of United States his­to­ry, indi­vid­u­als with intel­lec­tu­al dis­abil­i­ty were sen­tenced to death and exe­cut­ed, often with­out legal recog­ni­tion of how their impair­ments affect­ed their cul­pa­bil­i­ty, the reli­a­bil­i­ty of con­fes­sions, or their abil­i­ty to assist coun­sel. At least 44 peo­ple with intel­lec­tu­al dis­abil­i­ties were exe­cut­ed in the mod­ern era before the Atkins deci­sion rec­og­nized con­sti­tu­tion­al pro­tec­tions for them.27 
  • Legal pro­tec­tion devel­oped slow­ly. In 1989, the Supreme Court held in Penry v. Lynaugh that the Constitution did not cat­e­gor­i­cal­ly pro­hib­it the exe­cu­tion of indi­vid­u­als with intel­lec­tu­al dis­abil­i­ty, find­ing insuf­fi­cient nation­al con­sen­sus at the time. A shift over the fol­low­ing decade, how­ev­er, was rec­og­nized in Atkins when the Court not­ed that ​“a nation­al con­sen­sus has devel­oped against” exe­cut­ing peo­ple with intel­lec­tu­al dis­abil­i­ty.28 
  • More than two decades after Atkins, the con­sti­tu­tion­al rule is clear, but its appli­ca­tion remains uneven. State courts and leg­is­la­tures deter­mine who qual­i­fies for legal pro­tec­tion.29 In prac­tice, many dif­fer­ences in stan­dards and pro­ce­dures have affect­ed out­comes, and com­men­ta­tors and courts have not­ed that restric­tive approach­es will increase the risk that indi­vid­u­als with intel­lec­tu­al dis­abil­i­ty will still face exe­cu­tion.30 

Citation Guide
Footnotes

  2. American Bar Association, Evaluating Fairness and Accuracy in State Death Penalty Systems: The Alabama Death Penalty Assessment Report (2006), avail­able here.

  3. Atkins (2002) at 318. 

  4. Atkins (2002) at 317. 

  5. Hall v. Florida (2014) at 702 – 03.

  6. Moore v. Texas (2017) at 5 – 6.

  7. Moore v. Texas (2019) at 137 – 38.

  16. Georgia Resource Center, supra. 

  18. Georgia Resource Center, supra.

  19. The Guardian, supra.

  21. Innocence Project, supra.

  22. Courteney Stuart, Washington to Get $1.9M, C‑VILLE Weekly (Dec. 2007), https://c‑ville.com/washington_to_get_19_m/.

  23. Innocence Project, supra.

  25. The Washington Post, supra.

  26. Innocence Project, supra.