Black Mass (2015)

One of the most notorious criminals in the South Boston area and also the brother of the state senator, James "Whitey" Bulger became an Irish mob boss, while John Connolly, with whom he grew up on the streets of South Boston, became a successful FBI agent and the most important figure of the Boston office. Years later, when the two's paths cross again to eliminate their common enemy, the Italian mafia, John will persuade the mafia leader to cooperate with him.