WASHINGTON — The U.S. Supreme Court heard arguments Wednesday in a Texas death penalty case that could determine whether incarcerated people can pursue a second federal challenge to their sentences when advances in medical standards make previously unsuccessful constitutional claims potentially viable.
At issue in Guerrero v. Johnson is whether Dexter Johnson, a Texas death row prisoner, can pursue a claim under Atkins v. Virginia, the Supreme Court’s 2002 decision prohibiting the execution of people with intellectual disabilities, despite not raising that claim in his initial federal habeas corpus petition.
The case centers on the interpretation of federal restrictions on successive habeas petitions and whether a constitutional rule can be considered previously unavailable when changes in medical diagnostic standards make it applicable to an individual’s circumstances for the first time.
Johnson was convicted and sentenced to death in Texas for the 2006 killings of Maria Aparece and her boyfriend, Huy Ngo, during a robbery.
During sentencing, a defense psychologist compared Johnson’s intellectual functioning to that of a 10-year-old. However, because his IQ scores exceeded the threshold then used to diagnose intellectual disability, the psychologist did not complete an evaluation of his adaptive functioning.
The Texas Court of Criminal Appeals affirmed Johnson’s conviction in 2010.
Johnson filed his first federal habeas corpus petition in June 2011 without raising an intellectual disability claim.
While that petition was pending, the American Psychiatric Association published the fifth edition of its Diagnostic and Statistical Manual of Mental Disorders, known as DSM-5, in May 2013.
The revised diagnostic standards moved away from rigid IQ cutoffs and placed greater emphasis on adaptive functioning, including an individual’s ability to perform everyday tasks and function independently.
Under the revised criteria, Johnson’s earlier IQ scores would no longer automatically exclude him from consideration for an intellectual disability diagnosis.
His attorney did not amend the pending petition to raise an Atkins claim, instead seeking to add unrelated arguments. The federal district court denied the petition and the proposed amendment in August 2013.
The Fifth Circuit subsequently affirmed that decision in 2015.
The Supreme Court also addressed intellectual disability determinations in Hall v. Florida in 2014 and Moore v. Texas in 2017, emphasizing the importance of accepted medical standards rather than rigid IQ thresholds or nonclinical criteria.
In February 2019, Johnson sought additional state post-conviction review based on Atkins, but his petition was denied. His execution was subsequently stayed, and new counsel was appointed.
In August 2019, Johnson asked the U.S. Court of Appeals for the Fifth Circuit for permission to file a second federal habeas petition under 28 U.S.C. Section 2244(b)(2)(A).
That provision of the Antiterrorism and Effective Death Penalty Act of 1996, known as AEDPA, permits certain successive petitions based on a new constitutional rule made retroactive by the Supreme Court that was previously unavailable.
Johnson argued that although Atkins had been decided before his first petition, the constitutional protection was not meaningfully available to him under the diagnostic standards then applied.
The Fifth Circuit authorized the second petition, allowing Johnson to present evidence from subsequent psychological evaluations indicating that he meets current diagnostic criteria for intellectual disability.
Texas prison officials moved to dismiss the petition, arguing that it was both an impermissible successive filing and untimely.
Following an evidentiary hearing, the federal district court denied the motion to dismiss in October 2022, concluding that the Atkins claim had become available only after the diagnostic standards changed.
The court also applied equitable tolling, a doctrine permitting certain filing deadlines to be extended under exceptional circumstances, after determining that Johnson’s former attorney had deliberately declined to pursue an Atkins claim despite pursuing similar claims for other clients.
The district court’s ruling allowed Johnson’s second petition to proceed toward consideration of its merits but did not resolve whether he is constitutionally ineligible for execution.
Texas prison director Eric Guerrero appealed, arguing that the lower courts had improperly expanded the statutory exceptions governing successive petitions.
The Fifth Circuit affirmed the district court’s decision in July 2025 and denied rehearing before the full court in January 2026.
Judge James Ho dissented from the denial of rehearing, arguing that Johnson’s claim depended on changes in factual circumstances rather than a newly available constitutional rule.
The Supreme Court agreed to review the case June 15, 2026.
The central dispute concerns the meaning of the phrase “previously unavailable” in AEDPA.
Guerrero argues that the statute distinguishes between claims based on new constitutional rules and those based on newly discovered facts.
Under Section 2244(b)(2)(A), a successive petition may proceed when it relies on a qualifying new constitutional rule that was previously unavailable.
A separate provision, Section 2244(b)(2)(B), permits certain claims based on newly discovered facts, but requires evidence establishing that no reasonable factfinder would have found the applicant guilty of the underlying offense.
Guerrero maintains that Johnson cannot use the second provision because intellectual disability concerns eligibility for execution rather than guilt.
He also argues that Johnson cannot rely on the first provision because Atkins was decided in 2002, years before Johnson filed his initial federal petition.
Under the state’s interpretation, a constitutional rule is available once it has been announced by the Supreme Court, regardless of whether an individual prisoner could have successfully invoked it under the standards then in effect.
Johnson disputes that interpretation, arguing that a constitutional rule must have some possibility of providing relief to be considered available to a particular prisoner.
His attorneys maintain that the earlier diagnostic standards effectively prevented him from establishing intellectual disability, making an Atkins claim futile when his first federal petition was filed.
Johnson also argues that the statutory provisions governing new law and new facts are not mutually exclusive categories because constitutional claims necessarily involve applying legal rules to individual circumstances.
Under his interpretation, DSM-5 did not create new facts about his intellectual functioning but changed the diagnostic framework through which those facts were evaluated.
The dispute also involves whether subsequent Supreme Court decisions interpreting Atkins created new constitutional rules or clarified how the existing prohibition on executing intellectually disabled people must be applied.
Guerrero argues that Hall and Moore were not made retroactive by the Supreme Court and therefore cannot independently support Johnson’s successive petition.
Johnson responds that those decisions clarified the application of Atkins, which established a substantive constitutional protection against executing people with intellectual disabilities.
The case has also drawn arguments from victims’ advocates, criminal defense organizations and state governments concerning the consequences of allowing additional federal review.
Protasio Aparece, the father of Maria Aparece, submitted arguments supporting the state’s position, emphasizing the emotional and financial burdens that prolonged capital litigation can impose on victims’ families.
He argued that repeated challenges to death sentences can undermine confidence in final judgments and prolong the suffering of surviving family members.
The National Association of Criminal Defense Lawyers, supporting Johnson, argued that courts must be able to consider developments in scientific understanding when determining whether an execution would violate the Constitution.
The organization warned that excluding updated diagnostic evidence could leave people facing execution based on outdated medical assessments, even when contemporary clinical standards support an intellectual disability diagnosis.
Louisiana and 21 other states also supported restrictions on successive petitions, warning that allowing claims based on evolving diagnostic criteria could encourage repeated litigation, delay the enforcement of judgments and make evidence more difficult to evaluate over time.
Johnson’s supporters counter that AEDPA already imposes strict limitations on successive petitions and that recognizing changes in the practical availability of constitutional protections would not eliminate those restrictions.
The Supreme Court heard arguments Nov. 4 in Guerrero v. Johnson, No. 25-1003. The case remains pending, with the justices considering whether Johnson’s second federal habeas petition satisfies the statutory requirements for further review.
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