By Lawrence Hurley
WASHINGTON (Reuters) - U.S. Supreme Court justices appeared troubled on Monday by a judge's failure to step aside in a death penalty case he had previously worked on as a prosecutor involving a convicted murderer who killed a man who had sexually abused him as a minor.
The eight justices heard oral arguments in the Pennsylvania capital punishment case in an appeal brought by Terrance Williams, who was convicted of the 1984 bludgeoning murder of a 56-year-old man in Philadelphia in a crime committed when he was 18 years old.
Lawyers for Williams argued that former Pennsylvania Chief Justice Ronald Castille should have recused himself from hearing Williams' appeal as a member of the state Supreme Court because he had served as the local district attorney at the time of the conviction.
Although a majority of the U.S. Supreme Court signaled concern that Castille participated in the case, it was unclear exactly how the justices would rule. Some justices indicated it would be difficult to set rules that would determine exactly what level of involvement in a prior case should require a judge to recuse himself.
The case focuses on a December 2014 Pennsylvania Supreme Court ruling that upheld Williams' conviction and sentence. Castille had denied a recusal motion filed by Williams and was in the majority in the unanimous decision.
The normally nine-member Supreme Court is shorthanded following the Feb. 13 death of Justice Antonin Scalia.
(Reporting by Lawrence Hurley; Editing by Will Dunham)