As many as 100 people were crowded into the pantry of Los Angeles' Ambassador Hotel on June 5, 1968, when Sirhan Bishara Sirhan fired a 22-cal. revolver at Robert F. Kennedy. No one, as far as is known to this day, observed a second assassin. An autopsy and a far-reaching investigation by the FBI and local police persuaded authorities that Sirhan was the lone killer.
Yet challenges to that official conclusion have been building for years. In 1970 two film makers produced a feature documentary, The Second Gun, that questioned whether Sirhan fired the fatal bullet. Last May seeming conflicts in the...