The Supreme Court will hear oral argument on Nov. 4 in Guerrero v. Johnson, a case that probes the narrow circumstances under which a state prisoner may return to federal court for a second round of post-conviction habeas review. At issue is whether a claim invoking the Court’s 2002 decision in Atkins v. Virginia, which bars the execution of people with intellectual disabilities, was “previously unavailable” to the petitioner under federal law.
Under the Antiterrorism and Effective Death Penalty Act of 1996, prisoners face strict limits on filing successive habeas applications. As set out in 28 U.S.C. § 2244(b)(2), a new claim in a second federal petition is barred unless it falls into one of two narrow exceptions. The first permits a claim that “relies on a new rule of constitutional law, made retroactive to cases on collateral review by the Supreme Court, that was previously unavailable.” The second covers claims resting on the original case’s facts, but only if those facts would show by clear and convincing evidence that, absent constitutional error, no reasonable factfinder would have found the applicant guilty.
Guerrero v. Johnson and the ‘previously unavailable’ standard
Texas inmate Dexter Johnson invokes the first exception, arguing that he cannot be executed in light of Atkins. Johnson did not raise an Atkins-based intellectual disability claim in his initial petitions. After later qualifying as intellectually disabled under revised diagnostic criteria, he advanced the claim in a successive petition. The justices will decide whether Johnson’s Atkins claim was “previously unavailable” to him within the meaning of AEDPA.
Some background
Johnson was convicted in 2007 of capital murder and sentenced to death for his role in the killings of 23-year-old Maria Aparece and 17-year-old Huy Ngo. At trial, a defense expert placed Johnson’s IQ between 74 and 88 and testified that he had no obvious deficits in personal independence or social responsibility relative to peers of similar age and background. Under then-prevailing diagnostic standards, the expert concluded Johnson was not intellectually disabled. Johnson did not assert an Atkins intellectual disability claim in his initial habeas petitions, though he cited Atkins to argue, unsuccessfully, that its protection should extend to mental illness.
In May 2013, while Johnson’s federal petition was pending, the American Psychiatric Association released the DSM-5, which Texas’ highest criminal court adopted in 2018. The DSM-5 de-emphasized rigid IQ cutoffs and recognized that scores above 70 can still be consistent with intellectual disability. In April 2019, an expert administered an IQ test to Johnson yielding a score of 70, and a second expert concluded that Johnson met the DSM-5 criteria.
Johnson filed a successive habeas application in district court asserting that Atkins precludes his execution. Following an evidentiary hearing, the trial court found the Atkins claim “previously unavailable” and stayed his execution. The state appealed, and in July 2025 the U.S. Court of Appeals for the 5th Circuit affirmed. The en banc court declined rehearing by a 9-7 vote. The state petitioned for Supreme Court review in February, and the justices granted certiorari in June.
The parties’ arguments
The Office of the Texas Attorney General argues that Johnson’s claim does not rest on a change in law. Atkins predated Johnson’s initial habeas filing and even the offense conduct, the state notes, so the legal rule was available at the relevant time. Allowing Johnson’s claim, the state contends, would also undermine Congress’s distinction between new rules of law and new facts, because the DSM-5’s publication at most supplied a new factual predicate rather than altering the availability of any rule.
Texas further maintains that a rule can be available even if not useful to a litigant at the time. By contrast, Johnson’s counsel argues that a rule is available only if it can be used for a purpose. Before the DSM-5, they say, Atkins could not practically protect Johnson. They emphasize that Johnson himself did not change. The framework for evaluating intellectual disability did, making Atkins newly capable of application. They also dispute that recognizing unavailability here would open the floodgates, noting the rarity of retroactive constitutional rules.
The federal government, in an amicus brief supporting Texas, argues that professional diagnostic standards cannot convert an existing Supreme Court decision into a new or previously unavailable constitutional rule. Louisiana and 21 other states, also backing Texas, warn that the 5th Circuit’s approach invites endless Atkins litigation and undermines finality, pointing to changes in the age-of-onset criterion in 2021 as a potential source of further claims.
On Johnson’s side, the National Association of Criminal Defense Lawyers compares his claim to successive petitions grounded in improved forensic science, such as developments in microscopic hair analysis, arson science, and shaken baby syndrome. According to the group, constitutional claims tied to debunked or outdated analytical methods should be allowed to proceed when better science emerges.
Last term, after argument in Hamm v. Smith, a dispute over assessing multiple IQ scores in Atkins cases, the Court dismissed the matter as improvidently granted. Johnson asks the justices to do the same here, asserting that the state has shifted its theories. It is unlikely the Court will dismiss two Atkins cases in consecutive terms.
A decision in Guerrero v. Johnson is expected by late June or early July.