By Lawrence HurleyWASHINGTON (Reuters) - The U.S. Supreme Court on Monday agreed to hear a Louisiana man's appeal of a sentence of life in prison without parole that he received for murdering when he was 17 years old a police officer in 1963.The inmate, Henry Montgomery, is asking to be resentenced.The court will weigh the impact of one of its own rulings from three years ago that banned mandatory life sentences without parole for people who were under age 18 when they committed murder. The legal question is whether that ruling can be applied retroactively to inmates who were sentenced before the decision was issued.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, known as Miller v. Alabama.The court held 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 court's four liberals, while the other conservative members dissented.The decision did not mean that the prisoners must be released, only that they get the chance to seek parole.The Supreme Court had originally taken a separate case to decide the issue. But the defendant, George Toca, made a deal with prosecutors and was released from prison before the Supreme Court could issue a decision and the case was dismissed in February.A ruling in the new case is due by the end of June.(Reporting by Lawrence Hurley; Editing by Will Dunham)Join the conversation about this story Click here to read full news..