WASHINGTON (CN) – Blocking the execution of an intellectually disabled killer Tuesday, the Supreme Court slammed Texas for ignoring medical evidence in favor of Steinbeck characters.

Bobby James Moore has been on death row for killing a shop clerk in a botched April 1980 robbery that he had committed with two others when he was 20 years old.

Attorneys have argued that Moore’s intellectual disabilities go back to his childhood, however, when he was abused at home and took a brick to the head during battles to integrate Texas schools. When Moore was 13, experts have testified, he could not differentiate the days of the week, tell time or understand that addition is the opposite of subtraction.

Though a state habeas court initially determined that the Eighth Amendment prohibited Moore’s execution, the Texas Court of Criminal Appeals reversed, saying the habeas court had improperly given more weight to expert medical evidence than to precedent.

The CCA, as the court is often abbreviated, said habeas determinations need consider only the 1992 guidelines adopted in its case Ex parte Briseno. Among several nonclinical factors that guide the definition of intellectual disability in those guidelines are references to the slow fictional character Lennie from “Of Mice and Men.”

Four months after critical oral arguments in the case, the Supreme Court vacated the judgment against Moore 5-3 on Tuesday.

The majority opinion by Justice Ruth Bader Ginsburg says the Texas court failed to uphold the standard adopted in the 2014 case Hall v. Florida, which says adjudications of intellectual disability should be “informed by the views of medical experts.”

“That instruction cannot sensibly be read to give courts leave to diminish the force of the medical community’s consensus,” Ginsburg wrote. “Moreover, the several factors Briseno set out as indicators of intellectual disability are an invention of the CCA untied to any acknowledged source. Not aligned with the medical community’s information, and drawing no strength from our precedent, the Briseno factors ‘create an unacceptable risk that persons with intellectual disability will be executed.’ Accordingly, they may not be used, as the CCA used them, to restrict qualification of an individual as intellectually disabled.”

Detailing the overwhelming evidence of Moore’s disabilities, Ginsburg notes that as a boy he had been allowed to draw in class rather than drag down the lessons far outpacing him.

Moore became homeless after he failed every subject and dropped out of ninth grade.

“He survived on the streets,” the decision states, “eating from trash cans, even after two bouts of food poisoning.”

Though the CCA found that Moore’s IQ scores did not document him as intellectually disabled, it arrived at that conclusion by discounting five of the seven scores, and discounting the lower end of the standard-error range associated with the remaining two scores.

“Hall instructs that, where an IQ score is close to, but above, 70, courts must account for the test’s ‘standard error of measurement,’” Ginsburg noted.

Though the CCA had a duty to consider Moore’s adaptive functioning because of his low IQ scores, Ginsburg added, it deviated in this analysis “from prevailing clinical standards and from the older clinical standards the court claimed to apply.”

Ginsburg was adamant that the CCA’s reliance on its precedent impeded this assessment, calling the Briseno factors an outlier both in comparison to other states’ handling of intellectual-disability pleas and to Texas’ own practices in other contexts.

“No state legislature has approved the use of the Briseno factors or anything similar,” Ginsburg wrote. “In the 12 years since Texas adopted the factors, only one other state high court and one state intermediate appellate court have authorized their use.”

Ginsburg highlighted the incongruity of relying on Briseno factors only in the context of the death penalty but not in other settings, such as the assessment of a student’s intellect.

“Texas cannot satisfactorily explain why it applies current medical standards for diagnosing intellectual disability in other contexts, yet clings to superseded standards when an individual’s life is at stake,” the decision states.

Justices Clarence Thomas and Samuel Alito joined Chief Justice John Roberts in dissent, saying it is the majority not the CCA that subordinated medical evidence for legal theory.

“Clinicians, not judges, should determine clinical standards; and judges, not clinicians, should determine the content of the Eighth Amendment,” Roberts wrote. “Today’s opinion confuses those roles, and I respectfully dissent.”