The Supreme Court announced a ruling in the case Hall v. Florida, finding that the state had adopted too rigid a cutoff in deciding who is eligible to be spared the death penalty because of intellectual disabilities. (Chip Somodevilla/Getty Images)

The Supreme Court gave greater protection Tuesday to death row inmates seeking to prove they should not be executed because they are intellectually disabled, and it ruled that laws such as those in Florida and Virginia are too rigid.

The court ruled 5 to 4 that state laws that draw a bright line on IQ-test results are unconstitutional. Under those laws, an inmate who scores above 70 on the test does not meet the first step of proving that he or she is intellectually disabled and thus ineligible for the death penalty.

Florida, Virginia and Kentucky have such laws, and a handful of others have similar rules.

It was the court’s first consideration of state laws defining mental retardation in capital cases since its 2002 decision in Atkins v. Virginia that executing the mentally retarded violated the Constitution’s prohibition against cruel and unusual punishment.

In that decision, the court left it up to states to define intellectual disability. But those state determinations must meet constitutional requirements respecting “the gravest sentence our society may impose,” wrote Justice Anthony M. Kennedy in the majority opinion released Tuesday. He was joined in the decision by the court’s four liberals.

With capital punishment dominating headlines, PostTV looks at the latest statistics on the death penalty in the United States, and in the 21 other countries that executed inmates in 2013. (Davin Coburn/The Washington Post)

“Florida seeks to execute a man because he scored a 71 instead of a 70 on an IQ test,” Kennedy wrote, adding that experts agree that any number on an IQ test is an imprecise measurement. “Persons facing that most severe sanction must have a fair opportunity to show that the Constitution prohibits their execution. Florida’s law contravenes our nation’s commitment to dignity and its duty to teach human decency as the mark of a civilized world.”

It is relatively rare for a death row inmate to raise intellectual disability as a bar to execution. Defense lawyers in Virginia, for instance, estimate that the ruling might aid only a couple of the eight death row inmates there.

But the decision again showed the continuing tension among the justices about how to apply the “evolving standards of decency that mark the progress of a maturing society,” as the court put it more than 50 years ago, to the Constitution’s prohibition on cruel and unusual punishment.

In recent decisions, a bare majority has said that juveniles may not be executed and reaffirmed that the death penalty is a fitting punishment only for murder.

Justice Samuel A. Alito Jr., writing for the dissenters, said Kennedy’s reliance on the medical community’s view on how to consider the IQ tests rather than leaving it to states was a “sea change” in the court’s approach.

“What counts are our society’s standards — which is to say, the standards of the American people — not the standards of professional associations, which at best represent the views of a small professional elite,” Alito wrote.

State officials, too, said the justices continue to place additional hurdles in the way of enforcing the death penalty.

“First of all, they shouldn’t be sticking their nose into Virginia criminal law. The people get to decide what’s illegal in Virginia,” said Del. David B. Albo (R-Fairfax), chairman of the House Courts of Justice Committee.

A spokesman for Virginia Attorney General Mark R. Herring (D) said the office would “begin a review to determine what impact the ruling might have on pending or future capital cases and whether any statutes need to be amended to comply with it.”

The case before the court involved Freddie Lee Hall, 68, who has lived more than half his life on Florida’s death row. He was sentenced to death for raping and killing Karol Hurst, 21 years old and pregnant, after he and a co-defendant kidnapped her as she left a grocery store in 1978.

The men killed a police officer who interrupted their plans to rob a convenience store later that day.

Lawyers for Hall have argued in decades of court procedures that he should be spared because of a brutal childhood and because he has been identified since he was a boy, and later by some judges, as mentally retarded. (Kennedy wrote that the court was retiring that term with Tuesday’s ruling, and that “intellectual disability” would now be used.)

In the 2002 case Atkins v. Virginia, the court said defendants must show below-average intellectual functioning, along with deficits in “adaptive behavior” and proof that the onset of the intellectual disabilities began before age 18. In the ruling, the court said that IQ test number was “approximately” 70.

The Florida Supreme Court said the state’s law established 70 as a hard cutoff. Hall had several tests with a range of scores, including 71, 72, 73 and 80. With those, the Florida Supreme Court said he could not move on to the next stage of showing his disability.

But Kennedy wrote: “Intellectual disability is a condition, not a number.” He cited a brief from the American Psychological Association that said IQ tests should be read as a range of numbers rather than a specific figure. When a defendant falls within that range, Kennedy said, he must be able to present additional evidence of disability.

Kennedy was joined by Justices Ruth Bader Ginsburg, Stephen G. Breyer, Sonia Sotomayor and Elena Kagan.

Kennedy’s opinion was notable for the lofty language that often draws criticism from his detractors.

“The Eighth Amendment’s protection of dignity reflects the nation we have been, the nation we are, and the nation we aspire to be,” he wrote. “This is to affirm that the nation’s constant, unyielding purpose must be to transmit the Constitution so that its precepts and guarantees retain their meaning and force.”

Alito wrote that as a practical matter, the court was adopting a “uniform national rule that is both conceptually unsound and likely to result in confusion.”

Alito said that as he reads the majority decision, a defendant who scores between 71 and 75 on IQ tests must be allowed to present evidence of adaptive behavior problems, such as the inability to learn basic skills or adapt to changing circumstances. “That is a remarkable change in what we took to be a universal understanding of intellectual disability just 12 years ago,” he wrote.

He was joined by the rest of the court’s conservatives: Chief Justice John G. Roberts Jr. and Justices Antonin Scalia and Clarence Thomas.

In Virginia, defense lawyers specializing in death penalty cases said the ruling might aid a couple of inmates now on death row.

Alfredo R. Prieto, for instance, raised an intellectual disabilities claim on his lengthy road to death row. Prieto faced three trials before he was ultimately convicted of killing a man and woman near Reston in 1988.

Cary Bowen, Prieto’s defense attorney, said Tuesday that he believed the decision would prompt a hearing for his client.

“I believe that at least it opens the door for a fresh look at whether or not he can be given the death penalty, and that’s a big deal,” Bowen said. “But again, it will be the battle of the experts.”

The decision might also affect the case of Virginia death row inmate William J. Burns, who was convicted of raping and killing his mother-in-law. After being sentenced, Burns won a state court ruling that he could pursue a claim of intellectual disability.

The Supreme Court’s ruling came in Hall v. Florida.

Laura Vozzella contributed to this report.