Why Did Dignam Kill Sullivan And Who Was He Working For In The Departed (2006)?

Why Did Dignam Kill Sullivan And Who Was He Working For In The Departed (2006)?

The Departed is Martin Scorsese’s 2006 masterpiece starring Matt Damon, Vera Farminga, Jack Nicholson, and Leonardo DiCaprio. The movie is based on the 2002 Hong Kong action film Infernal Affairs. It follows two men on differing undercover missions – one is a police officer investigating an Irish mob, and the other is a rat planted in the police department by the gangsters. Besides being energetic and fast-paced, The Departed is brimming with crazy trivia and wild Easter eggs, one of which is the ending, where Sergeant Sean Dignam shot dead Colin Sullivan, the mole planted by mafia Frank Costello in the Massachusetts State Police. Such an ending came out of nowhere and was quite ambiguous, especially Sergeant Dignam’s motivations behind killing Sullivan. In this article, we will be discussing the same, and I will try to address all the questions you might have as we move.


Why Did Sergeant Dignam Kill Sullivan?


Former Sergeant Dignam shot down Sullivan to avenge the deaths of Captain Queenan and Billy Castigan Jr. after Dignam found out that Colin Sullivan was Frank the gangster’s mole.

Although I subscribe to the above explanation, there is another theory behind Dignam killing Sullivan – Dignam himself being the rat even though it was never mentioned in the movie. The fact that he went away on administrative leave for two weeks and came back to find about so many deaths probably to clean up the mess. 


What Does The Rat Symbolize In The Final Shot Of The Departed


The final shot projects a rat sniffing around and walking off the screen, which could symbolize that there always remains a rat, Dignam, in that case. The rat is a reference to the fact that there was and will always be someone keeping secrets or telling lies like police and criminals, men and women. Besides the obvious ones, innocent appearing women like Madolyn and Gwen Costello (Frank’s wife) could also be involved. Madolyn could be a liar as she told Colin that he was the father of her child, while I feel that it is actually Billy. The following three instances point towards the same fact-:

  1. It was established in the movie that Sullivan had “trouble” performing in bed.
  2. There is a sex scene involving Madolyn and Billy, and it was sometime after this scene when Madolyn confirmed that she was pregnant.
  3. After having received the conversation that Colin had with Frank, Madolyn said to Colin “And I thought I was the only liar.”


It also brings to my notice Frank Costello’s wife, Gwen. She was the woman who was always there in the background (shown doing her thing, of course), especially when Frank was having conversations over the phone. There were several shots of her lingering in the background, where she is listening in. That Madolyn and Gwen were liars or moles cannot be established with certainty, but they raise a few eyebrows and compel us to think deeper.


How Did Dignam Know Sullivan Was The Rat?


Although it is never explicitly mentioned in The Departed, it is implied that Dignam got to know that Colin Sullivan was a rat in the police department through one of the two sources-:

  1. The Envelope: Yes, I am talking about the envelope that Costigan gave to Madolyn that she wrote his name on and shoved into the drawer. It could have been Sullivan’s death warrant! It probably identified Sullivan as the rat and instructed Madolyn to go to Sergeant Dignam with the information if anything happened to Costigan.
  2. It is also possible that Costigan himself told Madolyn to go to Dignam when giving her the envelope.


Who Was Dignam Working For In The Departed?


Dignam’s killing of Sullivan raised several questions, one of which was – Who did Dignam work for when he killed Sullivan?

In all probability, Sergeant Dignam worked for the police department and most importantly, himself. The anger in Dignam’s face could be clearly seen when he came to shoot Sullivan. So it is safe to assume that Dignam acted out of vengeance for Costigana and Captain Queenan. It also brings me to point out that Dignam was not a rat because had he been a rat, he would not have hesitated as much. Also, Sullivan’s last line was “Okay” as he finally got caught. If he thought of Dignam being a rat too, he would have begged for his life and tried to strike a deal with Dignam instead of just saying “Okay”. Moreover, the fact that Dignam did not kill Madolyn also proves this. Madolyn knew a lot, and if Dignam were a rat, he would have taken her out as she could have been a threat to him.

So for Dignam, killing Sullivan was the only way to get justice for Captain Oliver Queenan, Billy Costigan, and others, especially considering that Sullivan had just gotten credits for “cracking the case” by naming Barrigan as a mole.

So here was my take on some ambiguous parts of The Departed. I hope this helped simplify some of those parts for you.