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: While the U.S. Supreme Court has barred the exe­cu­tion of indi­vid­u­als with intel­lec­tu­al dis­abil­i­ties, no such cat­e­gor­i­cal ban exists for those with severe men­tal ill­ness (SMI). Consequently, peo­ple suf­fer­ing from active psy­chosis, delu­sions, or severe neu­ro­bi­o­log­i­cal impair­ments remain eli­gi­ble for exe­cu­tion. Even with severe symp­toms, courts often rule that pris­on­ers meet the stan­dard for legal ​“com­pe­ten­cy” to be exe­cut­ed, con­clud­ing they still pos­sess a ratio­nal under­stand­ing of the con­nec­tion between their crime and their pun­ish­ment. Evidence of men­tal ill­ness can be pre­sent­ed as mit­i­gat­ing evi­dence at the sen­tenc­ing phase of a cap­i­tal tri­al, but juries do not always under­stand how men­tal ill­ness affects a defendant’s culpability.

Mental Health Statistics: 1976 to Date

  • 83% of indi­vid­u­als exe­cut­ed in 2025 had at least one sig­nif­i­cant vul­ner­a­bil­i­ty, includ­ing severe men­tal ill­ness, brain injury, or pro­found childhood trauma.
  • There is a cor­re­la­tion between exe­cu­tion ​“vol­un­teers” and severe men­tal ill­ness. A sig­nif­i­cant per­cent­age of exe­cu­tion vol­un­teers—those who waive their appeals to has­ten their exe­cu­tion — have a doc­u­ment­ed his­to­ry of severe men­tal ill­ness or substance abuse.
  • An esti­mat­ed 20 – 40% of the cur­rent death row pop­u­la­tion suf­fer from seri­ous mental illness.
  • Only 2 states (Ohio and Kentucky) have passed laws exempt­ing peo­ple with SMI from the death penalty.

Key Facts

The ​“Insanity” Defense at Trial is Rarely Successful. While a legal defense to the crime because of men­tal sta­tus at the time of tri­al is usu­al­ly avail­able, it is used in less than 1% of all felony cas­es and is suc­cess­ful in only a frac­tion. In cap­i­tal cas­es, the legal stan­dard often requires a defen­dant to prove they did not know ​“right from wrong,” a thresh­old that many peo­ple with active hal­lu­ci­na­tions or delu­sion­al dis­or­ders fail to meet at trial.

Traumatic Brain Injury (TBI) is a Silent Factor. Neurological dam­age is a major fac­tor in many death penal­ty cas­es. Research sug­gests that his­to­ries of TBI can impair the frontal lobe, which con­trols impulse reg­u­la­tion. Expert tes­ti­mo­ny is often required to help juries under­stand that emo­tion­al out­bursts and what they might per­ceive as a lack of remorse are the result of brain trauma.

Dismissal of Mental Health Evidence. Mental health evi­dence is fre­quent­ly dis­missed by pros­e­cu­tors or mis­un­der­stood by juries. In cap­i­tal tri­als, juries may view severe men­tal ill­ness not as a mit­i­gat­ing cir­cum­stance, but as an aggra­vat­ing fac­tor that proves the defen­dant is inher­ent­ly dan­ger­ous. This was appar­ent in the Texas tri­al of Andre Thomas. Despite his long, doc­u­ment­ed his­to­ry of severe schiz­o­phre­nia, pros­e­cu­tors suc­cess­ful­ly argued that his pro­found delu­sions and self-muti­la­tion were evi­dence of his ​“future dan­ger­ous­ness,” using the very symp­toms of his ill­ness as the pri­ma­ry aggra­vat­ing fac­tor to secure his death sentence.

Veterans and PTSD. Military vet­er­ans rep­re­sent a sig­nif­i­cant sub-pop­u­la­tion of death row affect­ed by men­tal ill­ness. In 2025, 10 vet­er­ans were exe­cut­ed, the high­est num­ber in near­ly two decades. Many of these indi­vid­u­als suf­fered from com­bat-relat­ed Post-Traumatic Stress Disorder (PTSD) or brain injuries sus­tained dur­ing mil­i­tary ser­vice, con­di­tions that were often inad­e­quate­ly pre­sent­ed or weighed dur­ing the sen­tenc­ing phase of their trials.

Legal Landscape

The U.S. Supreme Court has estab­lished sev­er­al legal stan­dards regard­ing how men­tal impair­ments affect death penalty eligibility:

  • Ford v. Wainwright (1986): Prohibits the exe­cu­tion of pris­on­ers who are ​“insane” and requires a com­pe­ten­cy eval­u­a­tion and hear­ing on the ques­tion of com­pe­ten­cy to be exe­cut­ed. However, this pro­hi­bi­tion only applies to a prisoner’s men­tal state at the time of exe­cu­tion, not at the time of the crime.
  • Atkins v. Virginia (2002): Prohibits the exe­cu­tion of peo­ple with intel­lec­tu­al dis­abil­i­ties (then termed ​“men­tal retar­da­tion”). Intellectual dis­abil­i­ty is a devel­op­men­tal con­di­tion dis­tinct from men­tal ill­ness, both med­ical­ly and legally.
  • Panetti v. Quarterman (2007): Prohibits the exe­cu­tion of a pris­on­er who does not have a ratio­nal under­stand­ing of why they are being exe­cut­ed. Simply know­ing that the state is killing them is not enough if, for exam­ple, a delu­sion pre­vents them from com­pre­hend­ing the pur­pose of the punishment.
  • Madison v. Alabama (2019): Prohibits the exe­cu­tion of a pris­on­er who can­not ratio­nal­ly under­stand the rea­son for their exe­cu­tion, even if that inabil­i­ty is caused by demen­tia rather than men­tal ill­ness or delu­sions. The Court also clar­i­fied that while mem­o­ry of the crime is not required for exe­cu­tion, there must still be a ratio­nal under­stand­ing of the con­nec­tion between the crime and the punishment.

Case in Point: Andre Thomas

The case of Andre Thomas in Texas high­lights the extreme nature of men­tal ill­ness on death row. Mr. Thomas, who suf­fers from severe schiz­o­phre­nia, killed his estranged wife and two chil­dren while expe­ri­enc­ing reli­gious delu­sions. While in jail await­ing tri­al, he removed one of his own eyes and ate it, believ­ing he was com­pelled to do so by the Bible; years lat­er, while on death row, he removed his remain­ing eye. Despite this indis­putable evi­dence of pro­found psy­chosis, Texas con­tin­ues to pur­sue his exe­cu­tion, spark­ing inter­na­tion­al out­cry over the inad­e­qua­cy of competency standards.

Global Perspective

The exe­cu­tion of per­sons with men­tal dis­abil­i­ties, includ­ing men­tal ill­ness, is wide­ly con­demned by inter­na­tion­al bod­ies. The United Nations Human Rights Committee has repeat­ed­ly urged states not to impose the death penal­ty on indi­vid­u­als with any form of men­tal dis­or­der, char­ac­ter­iz­ing the prac­tice as a vio­la­tion of the pro­hi­bi­tion of torture.

Internationally, there is an evolv­ing con­sen­sus against the death penal­ty for those with SMI. In 2021, the Supreme Court of Pakistan issued a land­mark judg­ment ban­ning the exe­cu­tion of pris­on­ers with severe men­tal ill­ness, stat­ing that pun­ish­ing those who can­not com­pre­hend the rea­son for their pun­ish­ment does not meet the ends of jus­tice. The European Union main­tains an absolute oppo­si­tion to the death penal­ty in all cir­cum­stances and has con­sis­tent­ly inter­vened in U.S. cas­es involv­ing for­eign nation­als with severe mental illness. 

Tags
Citation Guide