By Lawrence Hurley

WASHINGTON (Reuters) - The U.S. Supreme Court on Friday agreed to hear a Louisiana inmate's appeal of a sentence to life in prison without parole that he received after he was convicted, at the age of 17, of killing a friend 30 years ago.

In the case of George Toca, the court will weigh one of its own rulings from two years ago. That ruling banned mandatory life sentences without parole for people who were under 18 years of age when they committed murder. The legal question is whether the ruling can be applied retroactively to Toca.

In 1984, Toca was arrested at 17 for murdering his friend, Eric Batiste, during a failed armed robbery in New Orleans. In 1985, Toca was convicted and sentenced to life without parole. His lawyers say he is innocent.

Lower courts are divided over whether inmates who have already gone through the appeals process can benefit from the high court’s decision in the 2012 case, Miller v. Alabama.

The court held then on a 5-4 vote that the U.S. Constitution's ban on cruel and unusual punishments forbids such a mandatory sentencing scheme for juveniles convicted of murder. Conservative Justice Anthony Kennedy joined the liberals, while the more conservative members dissented.

The decision did not mean the prisoners must be released, only that they got the chance to seek parole.

A ruling is due by the end of June. The case is Toca v. Louisiana, U.S. Supreme Court, No. 14-6381.

(Editing by Kevin Drawbaugh and Lisa Von Ahn)