The US Constitution forbids the execution of killers who were under 18 when they committed their crimes the Supreme Cort ruled today, ending a practice used in 19 states.
The 5-4 decision throws out the death sentences of about 70 juvenile murderers and bars states from seeking to execute minors for future crimes.
The executions, the court said, were unconstitutionally cruel.
It was the second major defeat at the high court in three years for supporters of the death penalty.
Justices in 2002 banned the execution of the mentally retarded, also citing the Constitution's Eighth Amendment ban on cruel and unusual punishments.
The court had already outlawed executions for those who were 15 and younger when they committed their crimes.
Today's ruling prevents states from making 16 and 17-year-olds eligible for execution.
Justice Anthony Kennedy, writing for the majority, noted that most states do not allow the execution of juvenile killers and those that do use the penalty infrequently. The trend, he noted, was to abolish the practice.
The Supreme Court has permitted states to impose capital punishment since 1976 and more than 3,400 inmates await execution in the 38 states that allow death sentences.
Currently, 19 states allow executions for people under age 18: Alabama, Arizona, Arkansas, Delaware, Florida, Georgia, Idaho, Kentucky, Louisiana, Mississippi, Nevada, New Hampshire, North Carolina, Oklahoma, Pennsylvania, South Carolina, Utah, Texas and Virginia.
AP