The Lebanese killer of a U.S. Navy diver was in custody in Beirut yesterday, according to U.S. officials who decried his release from a German prison last week and pledged to bring him to the United States for trial. Relatives of the victim -- Waldorf, Md., native Robert Dean Stethem -- said yesterday they were "devastated" to learn of the killer's release and urged the Bush administration to demand an explanation from Germany. "Just to see him free slays us," said Richard Stethem, father of the seaman whose beaten body was thrown onto a Beirut runway in 1985. Mohammad Ali...