Continuity mistake: When Ellerby attacks the guy for not installing the cameras in the right place, he knocks off a map from the board. A second later Ellerby is still going after him, and the map is fixed.
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The Departed (2006)
Plot summary
Directed by: Martin Scorsese
Starring: Alec Baldwin, Mark Wahlberg, Matt Damon, Jack Nicholson, Leonardo DiCaprio, Martin Sheen
Two rats. One mob boss. Leonardo DiCaprio plays Billy, a trainee cop who has a bad family history. He is sent by Captain Queenan, played by Martin Sheen and Sergeant Dignam, played by the excellent Mark Wahlberg, to infiltrate the Boston mob, run by Jack Nicholsons Frank Costello. Matt Damon plays Colin, a policeman who rises fast through his ranks, but is secretly working for Costello. Both characters bounce off eachother, while never actually meeting, while each tries to find the others identity, while coming unknowingly close (both are interested in the same woman). That is the basic set up for this brilliantly tense mob thriller, directed by Martin Scorcese.
vashell
Surveillance Guy: Who the fuck are you?
Dignam: I'm the guy who does his job. You must be the other guy.
Trivia: This was Martin Scorsese's first film to win Best Picture. And his first Oscar for best Director. Martin also said that this was the first movie he ever made with a plot.
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Answer: The FBI and police are separate organizations that do not share full information. Only the FBI and Costello himself knew about the informing, and the FBI can only do so much to stop Costello being caught without drawing attention to their relationship. The police and Costello's gang are fighting a separate battle, hence the two moles.