Martin Scorsese’s adaptation of David Grann’s Killers of the Flower Moon is the latest turn in a long motion picture tradition of pilfering FBI case files for screen scenarios. Originally, Hollywood coveted the validation of the bureau (“based on actual FBI case histories!”) and the personal imprimatur of its lord high ruler, J. Edgar Hoover (who in 1945 actually read life insurance commercials for NBC radio’s This Is Your FBI). Today, it often takes cues without the…