WASHINGTON, D.C. — The U.S. Supreme Court heard arguments Wednesday over whether a Texas death row prisoner can pursue a constitutional challenge to his execution after changes in medical standards made it possible for him to establish an intellectual disability, despite federal restrictions on successive habeas corpus petitions.
The Nov. 4 hearing in Guerrero v. Johnson, No. 25-1003, centers on Dexter Johnson, who was sentenced to death in 2007 and argues that the constitutional prohibition against executing people with intellectual disabilities became applicable to his circumstances only after medical diagnostic standards changed.
The case requires the justices to interpret the Antiterrorism and Effective Death Penalty Act of 1996, which limits the circumstances under which incarcerated people can file additional federal habeas petitions challenging their convictions or sentences.
Under the law, a second petition may proceed when a claim relies on a new constitutional rule made retroactive by the Supreme Court that was previously unavailable, or when newly-discovered facts satisfy separate, stringent statutory requirements.
Johnson’s attorneys argue that the constitutional protection established in the Supreme Court’s 2002 decision in Atkins v. Virginia was not meaningfully available to him when he initially sought federal habeas relief.
In Atkins, the Supreme Court held that executing people with intellectual disabilities violates the Eighth Amendment’s prohibition against cruel and unusual punishment.
However, subsequent litigation has addressed how courts should determine whether someone qualifies for that constitutional protection.
Johnson was convicted of killing Maria Aparece and Huy Ngo during a robbery in Houston in 2006. He received a death sentence the following year.
At the time of his trial, Johnson’s IQ scores exceeded the threshold then used to evaluate intellectual disability, preventing a more comprehensive assessment of his adaptive functioning.
Johnson filed his first federal habeas petition in 2011 without asserting an intellectual disability claim.
In 2013, the American Psychiatric Association published the fifth edition of its Diagnostic and Statistical Manual of Mental Disorders, known as DSM-5, which moved away from rigid IQ cutoffs in diagnosing intellectual disability.
The Supreme Court subsequently addressed those diagnostic standards in Hall v. Florida in 2014, rejecting Florida’s use of a strict IQ threshold that prevented consideration of additional evidence.
In Moore v. Texas in 2017, the Court rejected Texas’ reliance on outdated, nonclinical factors when evaluating intellectual disability claims.
Following those developments, Johnson underwent additional psychological evaluations and presented evidence supporting his claim that he qualifies as intellectually disabled.
His attorneys sought authorization to pursue a second federal habeas petition, arguing that the constitutional protection recognized in Atkins had become available to him under the revised diagnostic framework.
The U.S. Court of Appeals for the Fifth Circuit permitted the petition to proceed, and a federal district court subsequently rejected Texas’ attempt to dismiss the case.
In July 2025, the Fifth Circuit affirmed the district court’s ruling, allowing Johnson’s intellectual disability claim to receive further consideration.
Texas prison director Eric Guerrero appealed, arguing that the Fifth Circuit had improperly expanded an exception to the federal law restricting successive habeas petitions.
Texas maintains that Atkins was already established law when Johnson filed his first federal petition and therefore cannot qualify as a previously unavailable constitutional rule.
The state argues that changes in medical diagnostic standards do not transform an existing Supreme Court precedent into a new constitutional rule.
Johnson’s attorneys counter that a constitutional protection cannot meaningfully be considered available when the diagnostic standards applied at the time would have prevented the claim from succeeding.
They argue that requiring incarcerated people to raise claims with no possibility of success would force them to file speculative challenges merely to preserve their ability to seek relief if medical or legal standards subsequently change.
The dispute also concerns the relationship between constitutional developments and newly-discovered evidence under federal habeas law.
Texas argues that Congress established separate requirements for claims based on new constitutional rules and claims based on new facts, and that Johnson cannot use changes in medical standards to circumvent those restrictions.
Johnson maintains that the revised diagnostic framework changed the legal standards used to apply Atkins, rather than merely providing newly discovered evidence.
The federal government participated in the Nov. 4 arguments in support of Texas, with Justice Department attorney Emily M. Ferguson appearing alongside Texas Solicitor General William R. Peterson.
Attorney Jeremy Schepers represented Johnson, according to the Supreme Court’s official hearing list.
The case also involves competing interests in the finality of criminal judgments and the constitutional prohibition against executing people with intellectual disabilities.
In an amicus brief supporting Texas, Protasio Aparece, the father of one of the murder victims, argued that repeated litigation prolongs suffering for victims’ families and undermines the finality of criminal judgments.
The National Association of Criminal Defense Lawyers submitted a brief addressing the importance of preserving access to federal review when constitutional claims become viable under subsequently clarified legal standards.
The Supreme Court granted review June 15, 2026, after the Fifth Circuit declined to reconsider its decision before the full court.
The justices must determine whether the statutory requirement that a constitutional rule be previously unavailable refers solely to when the Supreme Court announced that rule or whether its practical availability to an individual petitioner also matters.
A decision is pending.
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