Supreme Court Weighs the Constitutionality of the Death Penalty for the Intellectually Disabled

— -- The Supreme Court heard arguments today in Moore v. Texas, a case involving intellectual disability medical standards and the death penalty.

Bobby James Moore was convicted 36 years ago in the shooting death of James McCarble, a 70-year-old store clerk, in Houston, Texas.

After an appeals court again sentenced him to death, Moore's attorneys sought relief.

In June, the high court agreed to hear the case.

We spoke with ABC News' Supreme Court contributor Kate Shaw about today's case and what the court might decide:

What’s at Issue in This Case?

Kate Shaw: This case involves the question of who is constitutionally eligible for the death penalty. The Supreme Court has held that certain categories of individuals -- as relevant here, people with intellectual disabilities -- can’t be sentenced to death. The question here is what it means to have an "intellectual disability," and who decides.

What’s the Background?

In a 2002 case called Atkins v. Virginia, the Supreme Court held that the Constitution doesn’t permit the execution of people with intellectual disabilities. But the court left the states in charge of defining intellectual disability. For the most part, the court has let the states develop these definitions themselves, though in 2014 it intervened to hold that Florida could not use an IQ test alone. The question here is whether the standard Texas uses is constitutional.

What’s the Texas Standard, and What Are the Opposing Sides Arguing?

There’s a real debate between the opposing sides about both what Texas’s standard actually is, and what it should be.

Moore argues that Texas requires courts to use “outdated medical standards,” in particular a 1992 definition of intellectual disability, together with seven non-clinical “evidentiary factors” that in part make reference to the fictional character Lennie from John Steinbeck’s "Of Mice and Men." (For example, “Most Texas citizens might agree that Steinbeck’s Lennie should, by virtue of his lack of reasoning ability and adaptive skills, be exempt.”)

Moore argues that rather than “lay impressions, stereotypes and non-diagnostic criteria,” Texas must use current medical standards in determining death penalty eligibility.

Texas defends the 2004 Briseno factors as grounded in the very considerations the court has pointed to, and also argues that the lower court here did consider more recent diagnostic manuals in reaching its determination. Texas contends that Moore is asking the court to require Texas to use a particular definition of intellectual disability, drawn from the most recent edition of the American Association of Intellectual and Developmental Disabilities (AAIDD) and the DSM-5 (the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders).

Texas says nothing in the Constitution or the court’s cases requires it to do that. It also argues that Moore isn’t intellectually disabled, whatever the standard.

How Did Moore’s Case Get to the Supreme Court?

Moore was convicted of murder in Texas and sentenced to death prior to the Supreme Court’s 2002 Atkins decision. He subsequently received a hearing on his Atkins claim, and a trial court ruled that he was intellectually disabled and thus ineligible for the death penalty.

But the Texas Court of Criminal Appeals reversed that finding and concluded that Moore hadn’t established his intellectual disability. Moore asks the court to reverse that finding.

What Might the Court Decide?

It could hold that Texas cannot continue on its current course, but must use different and more current medical standards, which would mean Moore would get another hearing and potentially avoid the death penalty entirely. And a number of states look somewhat like Texas here, so if it did that, the implications could be much broader than just Moore, or just Texas. Justice Anthony Kennedy has voted with the court’s liberals on a number of death penalty cases, so Moore has a real chance of prevailing here.

Disclosure: Moore’s lawyer, Skadden's Cliff Sloan, has represented ABC News Supreme Court contributor Kate Shaw on a matter entirely unrelated to the subject of this case.