Croatian national and Communist historian was murdered by a fellow European in Astoria over a failed real-estate deal for a property in northeastern Italy, police source said. William Klinger, 42, was found Saturday with a gunshot wound to the head in Astoria Park near 19th Street, cops said. He died at Elmhurst Hospital. “Two young ladies found him face down,” said Chief of Detectives Robert Boyce. “Two bullet holes – one in his neck and one to the head”. Alexander Bonich, 49, also a Croatian national from Italy, was arrested Monday morning at his Queens apartment on 25-66 42nd Street. He told cops the two were friends.