The real events behind the highly-anticipated Warner Bros. film starring Sean Penn, Josh Brolin, Ryan Gosling and Emma Stone. full decade before J. Edgar Hoover's FBI even acknowledged the existence of the Mafia, the Los Angeles Police Department launched the real-life Gangster Squad -- eight men who met covertly and slept with Tommy guns while combating what city fathers saw as an "invasion of undesirables. But for two cops, Sgt. Jack O'Mara and Sgt. Jerry Wooters, all that mattered was nailing one strutting little gangster named Mickey Cohen.