WASHINGTON — The Supreme Court opened the door Monday to possible parole for hundreds of aging prisoners across the nation who are serving life terms for homicides committed when they were under age 18.

In a 6-3 decision, the justices said these prisoners can take advantage of an earlier ruling that called it cruel and unusual punishment to send a juvenile criminal to life in prison with no chance for parole.


Since then, California and most other states have given such prisoners a new sentence or provided them with a right to seek parole.

But several states, including Michigan, Pennsylvania and Louisiana, have refused to reopen old cases.

Monday's decision gave new hope to a 69-year-old Louisiana inmate who shot and killed a police officer in Baton Rouge in November 1963, days before President John F. Kennedy was assassinated in Dallas.

Henry Montgomery was 17 then and was sentenced to life in prison with no chance for parole.

Sixteen Marylanders are serving life without parole for crimes comitted as children, said James Johnston, director of the Maryland Office of the Public Defender's Youth Re-Sentencing Project. The youngest was 15 when the offense occurred.

There are many more Marylanders who are serving life sentences with parole, but the state's parole system "does not provide a realistic chance of release for juvenile lifers," Johnston said in a statement.

The ruling will have the most immediate effect in states with mandatory life without parole sentencing, which Maryland does not have, Johnston said. Still, he called the court's decision "a tremendous step toward meaningful relief for the hundreds of Maryland prison inmates who were tried and sentenced as children."

"We look forward to continuing to fight for reduced sentences and other relief for our juvenile clients statewide who are serving life without parole and life sentences," Johnston said.

Justice Anthony Kennedy has played the key role in a series of decisions that have restored the principle that young offenders should not be treated the same as hardened adult criminals.

In Monday's opinion, he said these prisoners do not have an automatic right to go free, but they do have a right to a parole hearing or a new sentence that limits their prison terms.

"Children are constitutionally different from adults in their level of culpability," and "prisoners like Montgomery must be given the opportunity to show their crime did not reflect irreparable corruption, and if it did not, their hope for some years outside prison walls must be restored," Kennedy said.

Kennedy spoke for the court in 2005 when the justices abolished the death penalty for juvenile murderers.