WASHINGTON — The Supreme Court on Thursday declared an end to the execution of convicted murderers who are mentally retarded, saying the nation has reached a consensus that it is cruel and unusual to put to death a person with the mental age of a child.
Eighteen states that impose the death penalty have passed new laws exempting prisoners who are retarded, the court said. In the last decade, only five states--most notably Texas--have executed killers whose IQs measured 70 or less, the standard threshold for defining retardation.
"The practice, therefore, has become truly unusual," said Justice John Paul Stevens, speaking for the court.
It is also cruel, he said, since those with a diminished mental capacity are more likely to act on impulse and less likely to consider the consequences.
The ultimate punishment of death should be reserved for the worst of murderers, Stevens said. Since retarded people are less culpable for their acts of violence, they must be "categorically excluded" from capital punishment, he concluded.
Thursday's 6-3 ruling extends to all of the 3,701 inmates condemned to death around the nation, as well as to future cases. California has by far the nation's largest death row, with 603 inmates. A state prosecutor predicted that very few of them will be spared by the ruling.
Justice Antonin Scalia read an angry dissent in the courtroom, accusing his colleagues of adopting the "arrogant assumption ... [that they] have moral sentiments superior to those of the common herd."
He mocked the "empty talk of a national consensus" on the issue and predicted that the ruling will cause chaos.
"The symptoms [of retardation] can be feigned ....This will turn the process of a capital trial into a game," he said. Chief Justice William H. Rehnquist and Justice Clarence Thomas joined his dissent.
Stevens said the court was reluctant to define mental retardation and left that task to experts, trial judges and state legislators.
However, his opinion relied on the standard used by the American Psychiatric Assn. and the American Assn. on Mental Retardation. These groups define mental retardation as a "significant sub-average general intellectual functioning." Typically, "mild" mental retardation describes people whose IQ level is measured from 50 to 70.
This intellectual deficiency must be combined with a limited "adaptive function" at home, at school or at work. "The onset [of these difficulties] must occur before age 18," the psychiatric association said.
