A divided Supreme Court abolished the death penalty yesterday for killers younger than 18, saying a "line must be drawn" barring a practice out of use in most states and banned by nearly every other country in the world.
The court's 5-4 ruling reversed a 1989 decision allowing capital punishment for killers who were 16 or 17 at the time of their crimes, relying on an "evolving standard of decency" in American society and new research suggesting that teen murderers are less culpable than adult counterparts.
"The differences between juvenile and adult offenders are too marked and well understood to risk allowing a youthful person to receive the death penalty despite insufficient culpability," Justice Anthony M. Kennedy wrote in the majority opinion.
Kennedy, a conservative regarded as a key swing vote in the closely watched case, joined the court's four liberal members in ruling that imposing the death penalty for offenders under 18 constitutes cruel and unusual punishment, a violation of the Constitution's Eighth Amendment.
The court's reasoning closely tracked a 6-3 decision from 2002 that barred the death penalty for the mentally retarded. In that case, Justice Sandra Day O'Connor joined the majority. But in a dissent yesterday, she rejected comparisons between the two issues.
"It defies common sense to suggest that 17-year-olds as a class are somehow equivalent to mentally retarded persons with regard to culpability or susceptibility to deterrence," O'Connor wrote. "The fact that juveniles are generally less culpable for their misconduct than adults does not necessarily mean that a 17-year-old murderer cannot be sufficiently culpable to merit the death penalty."
Yesterday's ruling in the case of a Missouri man sentenced to death for robbing and killing a woman when he was 17 means that about 70 death row inmates across the country sentenced for killings when they were under 18 now face life in prison.
It also ended any possibility that prosecutors would seek a new trial to try to gain a death sentence for convicted sniper Lee Boyd Malvo, who was 17 when he helped carry out the shootings that paralyzed Washington, D.C., suburbs in 2002.
The court's ruling was cheered by death penalty opponents and by international and human rights groups that had filed friend of the court briefs supporting the Missouri inmate, Christopher Simmons. The groups had argued that the United States was virtually alone in the world - joined only by Somalia - in maintaining the death penalty for juvenile offenders.
Marsha Levick, legal director of the Juvenile Law Center in Philadelphia, said the ruling brought the death penalty in line with other U.S. laws concerning juveniles.
"We exclude minors from society in both significant and trivial ways," Levick said. "They cannot vote, enlist in the military, sit on juries or even get tattoos. The court has now brought their eligibility in line with those exclusions."
But death penalty supporters and advocates for victims rights said the decision undercuts the right of lawmakers in each state to determine who faces capital punishment.
"You really have to wonder if they understand the depth of their decision - to just automatically give all teenage killers an exemption from the death penalty," said Mona Mills of Louisville, Ky., whose sister was the victim in the 1989 case in which the high court upheld the death penalty for killers 16 or older.
The modern death penalty was reinstated by the Supreme Court in 1976, and 22 of the prisoners executed since then were juveniles when they committed their crimes, according to the Washington-based Death Penalty Information Center, which tracks capital punishment statistics.
Nineteen states allow the execution of juveniles, but yesterday's majority ruling noted that only three - Texas, Virginia and Oklahoma - have executed juvenile offenders in the past 10 years.
Missouri's high court said the practice should be barred as "cruel and unusual" in overturning the death sentence of Simmons, who was 17 in September 1993 when he broke into the home of Shirley Crook, robbed her, wrapped her head and hands in duct tape and pushed her from a railroad bridge into a river.
Simmons confessed to the killing, which he planned with two teenage friends after assuring them that "their status as juveniles would allow them to get away with it," according to court briefs filed by Missouri Attorney General Jeremiah W. "Jay" Nixon.
Even before Simmons' case reached the Supreme Court, its four most liberal justices - John Paul Stevens, David H. Souter, Ruth Bader Ginsburg and Stephen G. Breyer - had gone on record in 2002 as calling the death penalty for juveniles a "shameful" practice.
While Kennedy and O'Connor were considered swing votes, the court's remaining three justices - conservatives Antonin Scalia, Clarence Thomas and Chief Justice William H. Rehnquist - have long made plain their support for the death penalty and filed a joint dissent yesterday.
"The court says in so many words that what our people's laws say about the issue does not, in the last analysis, matter," Scalia wrote. "The court thus proclaims itself sole arbiter of our nation's moral standards."