(Adds details of ruling and reaction)
By Lawrence Hurley
WASHINGTON, May 27 (Reuters) - The U.S. Supreme Court on Tuesday threw out a Florida man's death sentence by finding that the state's method for assessing whether defendants are mentally disabled violated the U.S. Constitution.
The court ruled on a 5-4 vote that Freddie Lee Hall, 68, who was on death row for two murders, should have another chance to show he should not be executed.
The decision gives states less latitude in deciding how to determine eligibility for the death penalty of people who say they are mentally disabled.
The ruling follows a 2002 decision in which the high court said the mentally disabled cannot be executed. It could help other inmates in Florida and some other states who are challenging their sentences.
Florida had initially determined that Hall was mentally disabled in 1992, but later found him competent after he scored 71 on an IQ test, the minimum under Florida law.
The court found that the Florida process was unlawful under the Eighth Amendment to the U.S. Constitution, which bans cruel and unusual punishment.
"Florida's law contravenes our nation's commitment to dignity and its duty to teach human decency as the mark of a civilized world," Justice Anthony Kennedy wrote on behalf of the majority.
The Supreme Court concluded that states should defer to the clinical consensus for determining whether people are mentally disabled.
Hall's attorneys said experts, including the American Psychiatric Association, said that IQ tests should include a standard error of measurement of five percentage points, meaning results could vary that much either higher or lower.
Florida's test has a hard cutoff at 70 on the IQ test and does not take into account the standard error of measurement.
Writing on behalf of the four dissenters, Justice Samuel Alito wrote that the court had embraced a "uniform national rule that is both conceptually unsound and likely to result in confusion."
Hall was convicted of the 1978 shooting deaths of a sheriff's deputy and a woman who was seven months pregnant. Only his death sentence was at issue in the case.
Jenn Meale, chief spokeswoman for Florida's Republican attorney general, Pam Bondi, declined to comment, saying officials were reviewing the decision.
The American Civil Liberties Union's state executive director, Howard Simon, said he hoped that the ruling signaled increased Supreme Court scrutiny of Florida's capital punishment laws and court procedures.
"The strict IQ rule struck down by the Supreme Court today is just one example of the many ways in which our state's death penalty system falls short of constitutional and human rights standards," he said.
The civil rights group opposes the death penalty.
Kennedy was joined in the majority opinion by Justices Ruth Bader Ginsburg, Elena Kagan, Sonia Sotomayor and Stephen Breyer. In addition to Alito, the dissenters were Chief Justice John Roberts and Justices Antonin Scalia and Clarence Thomas.
The case is Hall v. Florida, U.S. Supreme Court, No. 12-10882. (Additional reporting by Bill Cotterell in Tallahassee.; Editing by Howard Goller, Dan Grebler and Jonathan Oatis)