Justice Sandra Day O’Connor, the first woman to sit on the United States Supreme Court, died at the age of 93 on December 1, 2023. In her 25-year tenure on the Court, Justice O’Connor authored opinions in several landmark death penalty cases, including decisions that upheld the use of the death penalty for vulnerable groups and people with diminished culpability. However, she demonstrated an early interest in improving capital defense standards, and in her later years on the Court expressed concerns that the country had executed innocent people. Her legislative experience, a rarity for justices, influenced her approach in Eighth Amendment cases where she consistently looked to state legislatures to determine “evolving standards of decency” regarding the groups of people eligible for death.

Architect of Ineffective Assistance of Counsel Legal Standard 

Justice O’Connor set the seminal standard for judging the constitutional adequacy of defense representation in death penalty cases as the author of the majority opinion in Strickland v. Washington (1984), the Court’s first major foray into the assessment of defense representation under the Sixth Amendment. In Strickland, she held that in order to prevail, defendants raising ineffective assistance of counsel claims must show 1) that counsel’s performance was deficient, and 2) that the deficient performance prejudiced the defense. However, she declined to specify what “deficient” or “prejudicial” performances would look like, and emphasized that “judicial scrutiny of counsel’s performance must be highly deferential.” The majority’s reasoning came under severe criticism from Justice Thurgood Marshall in dissent:  

My objection to the performance standard adopted by the Court is that it is so malleable that, in practice, it will either have no grip at all or will yield excessive variation in the manner in which the Sixth Amendment is interpreted and applied by different courts. To tell lawyers and the lower courts that counsel for a criminal defendant must behave ‘reasonably’ and must act like ‘a reasonably competent attorney,’ is to tell them almost nothing.” 

Justice Marshall’s concerns proved prescient. A 2000 paper found “little consistency within judicial districts or across districts” in applying Strickland, with “striking…factual similarity between winners and losers.” Defendants were denied relief when courts found they had received “reasonable” representation despite their attorneys being impaired with drugs and alcohol, sleeping, and failing to present any evidence during trial. In a 2001 speech expressing concerns about the fair administration of the death penalty, Justice O’Connor herself suggested further action was needed: “Perhaps it’s time to look at minimum standards for appointed counsel in death cases and adequate compensation for appointed counsel when they are used.” Then, in 2003, she authored the majority opinion in Wiggins v. Smith, in which she wrote that the definition of “reasonable” could be found by looking to prevailing professional norms, such as the American Bar Association’s Guidelines for the Appointment and Performance of Defense Counsel in Death Penalty Cases. By doing so, Wiggins gave the courts specific guidance to evaluate attorney performance but upheld the use of a broad standard that invited judicial subjectivity and inconsistency.   

Legislative-Driven Approaches to Youthfulness, Mental Illness, and Intellectual Disability 

Unlike the other justices of her era, and as an outlier in the Court’s history, Justice O’Connor had served as a legislator for two terms in the Arizona State Senate prior to joining the Court. When the Court was called upon to decide whether the death penalty was “cruel and unusual punishment” for certain classes of people under the Eighth Amendment, she was a strong believer in the “evolving standards of decency” test—the notion that courts should look to the people for a consensus on the morality of a given practice. She argued that legislatures were the key signifiers of society’s views. However, her assessments of legislative trends were not always consistent, and her approach tended to favor state autonomy over death penalty practices, in line with her conservative colleagues. She disfavored blanket exclusions of vulnerable groups from the death penalty but was willing to grant relief based on individualized facts.    

Justice O’Connor resisted the idea that young offenders should be excluded from the death penalty. She concurred in the Court’s judgment in Thompson v. Oklahoma (1988) that the defendant, who had been 15 at the time of the crime, could not be executed, but wrote separately to question the plurality’s holding that all defendants under 16 should be categorically excluded. The Court found that 32 states rejected the practice or the death penalty generally. “Although I believe that a national consensus forbidding the execution of any person for a crime committed before the age of 16 very likely does exist, I am reluctant to adopt this conclusion as a matter of constitutional law without better evidence than we now possess,” she wrote. In Stanford v. Kentucky (1989) the following year, she became the swing vote in the Court’s conclusion that the death penalty was constitutional for children ages 16 and up, despite a majority of states rejecting the practice and a similar number to Thompson: 28 either declined to impose it on 16-year-olds or had abolished the death penalty outright. “The day may come when there is such general legislative rejection of the execution of 16- or 17-year-old capital murderers that a clear national consensus can be said to have developed,” she wrote in a concurrence, but “I do not believe that day has yet arrived.”  

In Roper v. Simmons (2005), the Court overturned Stanford and held that execution was only constitutional for defendants 18 or older at the time of their crime. Justice O’Connor dissented, despite the number of states rejecting capital punishment under 18 years old having grown to 30. The “evidence before us fails to demonstrate conclusively that any such consensus has emerged in the brief period since we upheld the constitutionality of this practice” in Stanford, she wrote, and she “would not substitute our judgment about the moral propriety of capital punishment for 17-year-old murderers for the judgments of the Nation’s legislatures.” Instead, she “would demand a clearer showing that our society truly has set its face against this practice before reading the Eighth Amendment categorically to forbid it.” Neuroscientific research now confirms that brains do not develop fully until a person’s mid-20s, meaning that impulse control, long-term planning, and other critical thinking faculties are inhibited in youthful offenders.   

Yet a 30-state agreement sufficed to form a “national consensus” around rejecting the death penalty for people with intellectual disability, in an illustration of Justice O’Connor’s fluctuating approach to death penalty analysis. She wrote for the majority in Penry v. Lynaugh (1989) upholding the practice, holding that “there is insufficient evidence of a national consensus against executing [intellectually disabled] people convicted of capital offenses for us to conclude that it is categorically prohibited by the Eighth Amendment.” However, she voted to grant relief to the defendant in that case and its companion case Penry v. Johnson (2001) on the grounds that Texas’ jury instructions did not allow the jury to meaningfully consider the defendant’s intellectual disability as a mitigating factor. By 2002, she joined the majority in Atkins v. Virginia to categorically bar the death penalty for people with intellectual disability, based in part on the fact that 30 states either banned the practice or the death penalty. The Court highlighted the “dramatic shift in the state legislative landscape” since Penry I that saw 16 new states pass bills on the subject.  

Justice O’Connor also resisted a categorical bar on executions for seriously mentally ill people. In Ford v. Wainwright (1986), where the Court held that the execution of a person with insanity was unconstitutional, she concurred in the judgment but dissented from the rationale. The “Eighth Amendment does not create a substantive right not to be executed while insane,” she wrote. Further, she disagreed “that the federal courts should have any role whatever in the substantive determination of a defendant’s competency to be executed.”   

Nonetheless, Justice O’Connor wrote forcefully against the “originalism” approach that some of the Court’s conservative justices now advocate, and which over a dozen state Attorneys General recently asked the Court to implement in place of the “evolving standards of decency” test. “It is by now beyond serious dispute that the Eighth Amendment’s prohibition of ‘cruel and unusual punishments’ is not a static demand,” Justice O’Connor wrote in her Roper dissent. “Its mandate would be little more than a dead letter today if it barred only those sanctions—like the execution of children under the age of seven—that civilized society had already repudiated in 1791.”  

Cementing the Death Penalty for Non-Triggermen 

Justice O’Connor was instrumental in maintaining the death penalty for people who participated in capital crimes but did not themselves kill—typically people convicted under “felony murder” laws. In Enmund v. Florida (1982), the Court held that the death penalty is unconstitutional when a defendant did not kill, attempt to kill, or intend that a killing take place. In her first year on the job, Justice O’Connor wrote for the four-justice dissent. Arguing that other Eighth Amendment decisions had stronger legislative and jury support, such as the abolition of the death penalty for rape in Coker v. Georgia (1977), she wrote that “the available data do not show that society has rejected conclusively the death penalty for felony murderers.” Five years later, she wrote for the 5-4 majority in Tison v. Arizona (1987) to further narrow the scope of Enmund. She held that a person who did not cause death nor intend to cause death could be executed if the jury found “major participation in the felony committed, combined with reckless indifference to human life.”  

In Later Years, Shared Public Concerns About Innocence 

Towards the end of her tenure on the Court, Justice O’Connor questioned the death penalty’s fairness several times in public speeches, emphasizing the emerging evidence of innocent people on death row. “More often than we want to recognize, some innocent defendants have been convicted and sentenced to death,” she said at a Nebraska State Bar Association event in 2001. She stated that wrongful convictions would continue to occur unless indigent defendants were represented by qualified lawyers. That same year, she told the Minnesota Women Lawyers organization that “serious questions are being raised about whether the death penalty is fairly administered in this country.” She referred to the then-90 (now 195) exonerations from death row, saying that “if statistics are any indication, the system may well be allowing some innocent defendants to be executed.” Research suggests that the same groups for whom Justice O’Connor voted to maintain the death penalty for many years–people who are under the age of 18, intellectually disabled, mentally ill, or lesser participants in the crime—face a heightened risk of wrongful conviction. Justice O’Connor retired from the Court in 2006 after 25 years of service.


Amicus Brief of Idaho and 13 Other States, Commissioner v. Smith, No. 23 – 167 (2023); Sean Doolittle, The Felony Murder Conundrum, Boston College Law School Magazine Online, March 24, 2023; Press Release, APA calls for extend­ing inel­i­gi­bil­i­ty for the death penal­ty to ado­les­cent offend­ers younger than age 21, American Psychological Association, August 4, 2022; Alexis E. Carl, Dead Wrong: Capital Punishment, Wrongful Convictions, and Serious Mental Illness, 1 Wrongful Conv. L. Rev. 336 (2020); Sheri Johnson, John H. Blume, and Amelia Courtney Hritz, Convictions of Innocent People with Intellectual Disability, 82 Albany L. Rev. 1031 (2018); Joshua A. Tepfer, Laura H. Nirider, and Lynda M. Tricarico, Arresting Development: Convictions of Innocent Youth, 62 Rutgers L. Rev. 887 (2009); Roper v. Simmons (2005); Wiggins v. Smith (2003); Atkins v. Virginia (2002); Penry v. Johnson (2001); Associated Press, O’Connor Questions Death Penalty, New York Times, July 4, 2001; Amy R. Murphy, The Constitutional Failure of the Strickland Standard in Capital Cases Under the Eighth Amendment, 63 Law and Contemporary Problems 179 (2000); Editorial Board, Innocents on Death Row, New York Times, May 23, 1999; Gina Kolata, DNA Tests Provide Key to Cell Doors for Some Wrongly Convicted Inmates, New York Times, August 5, 1994; American Bar Association, Guidelines for the Appointment and Performance of Defense Counsel in Death Penalty Cases (1989); Penry v. Lynaugh (1989); Stanford v. Kentucky (1989); Thompson v. Oklahoma (1988); Tison v. Arizona (1987); Strickland v. Washington (1986); Ford v. Wainwright (1986); Enmund v. Florida (1982); Coker v. Georgia (1977)