How Did Dignam Know Sullivan Was the Rat?

One of cinema’s most famous crime drama thrillers, The Departed swiftly gained widespread acclaim and achieved significant financial success, grossing over $291 million during its theatrical run.

Adding to that, it earned four Oscars, including Scorsese’s long-awaited victory for Best Director. This movie could also see a return in the form of a TV show, although this a speculation.

The Departed follows Billy Costigan (Leonardo DiCaprio), who assumes the role of an undercover police officer in crime-ridden South Boston. His mission is to infiltrate the mob syndicate led by Frank Costello (Jack Nicholson) and ultimately earn his trust.

Simultaneously, Colin Sullivan (Matt Damon), a seasoned criminal with connections to Costello’s organization, ascends the ranks within the police force while secretly working as an informant for the mob.

Both protagonists become fully immersed in their dual lives, always at the risk of exposure. Survival hinges on exposing the other’s true identity, but the depth of their involvement as undercover agents makes it an exceedingly difficult task.

Keep reading for a breakdown of the events leading to a very intense ending. For those who haven’t seen the movie, spoilers ahead!

Why Did Sullivan Get Shot at the End of The Departed?

In the movie’s gripping finale, many characters meet their demise, leaving only Colin Sullivan as the lone survivor. After several years of serving as a spy for the mob, he remains the only one aware of his betrayal.

However, his secret is at risk of being exposed when his girlfriend, Madolyn Madden (Vera Farmiga), receives incriminating evidence against him through an envelope that Costigan gave her in case anything was to happen to him. The envelope exposed Sullivan to be the rat with his ties to Costello and also revealed his role in Costigan’s death.

This envelope reaches Dignam, presumably through Madolyn, which blows his cover and causes Dignam to exact revenge on him by killing him in his apartment.

Even if Madden chose not to disclose the contents of the envelope, Sullivan could not evade the imminent possibility of his cover being blown.

What Is the Meaning of the End of the Movie Departed?

We see this theme throughout the movie, wherein characters inevitably face the consequences for their deceptive nature, with no one able to conceal their true identity indefinitely. Despite Colin’s belief that he could escape unscathed, the constant threat of his girlfriend knowing the truth weighs heavily on him.

In the case of Sullivan, it eventually catches up to him when Sergeant Dignam (Mark Wahlberg) shoots him in his apartment at the end of the movie.

Presumably, Madden takes the envelope to the police after Costigan’s funeral, which means that Dignam would have all the necessary evidence to exact revenge on Sullivan for his actions throughout the movie.