Black Mass (2015)

Directed by Scott Cooper, Black Mass stars Johnny Depp as Boston crime boss James “Whitey” Bulger in a true-crime story about organized crime, FBI corruption and violent underworld power. Based on the book Black Mass: Whitey Bulger, the FBI, and a Devil’s Deal, the film follows Bulger’s relationship with FBI agent John Connolly and the deal that allowed his criminal empire to grow. Joel Edgerton, Benedict Cumberbatch and Jesse Plemons co-star in this crime film about loyalty, corruption and gangster violence.

Från IMDB:
The true story of Whitey Bulger, the brother of a state senator and the most infamous violent criminal in the history of South Boston, who became an FBI informant to take down a Mafia family invading his turf.