The original trailer for this movie was pulled after the Aurora, Colorado Century 16 massacre due to a shot in which four gangsters fire machine guns through a projection screen into a crowded movie theater. Warner Bros. then ordered the film back into production for a reshoot of the scene, necessitating a rescheduling of the film's release and rewrite of the script.
In the movie, the Gangster Squad is assembled to go after Mickey Cohen. However in real life Chief Parker set up the squad to prevent other gangsters from taking over Cohen's rackets after Cohen went to prison on income tax evasion. Whenever the squad learned that an out-of-town gangster was coming to Los Angeles to try and set up new operations, the Gangster Squad would kidnap them, beat them up (some rumors say torture) and then send them back to wherever they came from with the warning that if the gangster ever returned, he would be killed.