What Happens to Sullivan at the End of The Departed?

At the end of The Departed (2006), Colin Sullivan (played by Matt Damon) is shot and killed by Staff Sergeant Sean Dignam (Mark Wahlberg). Sullivan is ambushed in his apartment after returning from the funeral of Billy Costigan. Dignam, wearing plastic medical booties to avoid leaving forensic evidence, executes Sullivan as retribution for his betrayals.

The ending of the film is one of the most discussed in modern cinema, particularly due to the sudden nature of Sullivan’s death and the symbolic presence of a rat on the balcony. For many viewers, the visual of the "boots"—the blue surgical covers worn by Dignam—remains the most striking detail of the scene.

The Death of Colin Sullivan: A Detailed Breakdown

In the final moments of Martin Scorsese’s crime masterpiece, Colin Sullivan believes he has successfully navigated his way out of his double-life as a mole for Frank Costello. Having orchestrated the deaths of both Costello and his rival undercover officer, Billy Costigan, Sullivan has erased nearly all evidence of his corruption.

The Ambush

Sullivan returns to his luxury apartment, carrying groceries, seemingly ready to start a new, "clean" life. As he enters the hallway, he notices something is wrong. Staff Sergeant Sean Dignam is waiting for him inside the apartment. Dignam is dressed in a tracksuit and is notably wearing plastic surgical booties (the "boots" often referred to by viewers).

Without a long exchange of dialogue, Dignam raises a suppressed pistol. Sullivan, realizing his fate is sealed and that there is no way to talk his way out of this situation, simply says, "Okay," before Dignam shoots him in the head. Sullivan dies instantly.

Why the "Boots" Matter

The inclusion of the plastic booties is a technical detail that serves both a narrative and aesthetic purpose. From a narrative standpoint, it confirms that Dignam is acting as a professional "cleaner" or vigilante. He is not there to make a statement; he is there to execute a traitor without leaving a trace of DNA or a footprint that could link him to the crime.

Aesthetically, the sight of the bright blue plastic covers against the high-end flooring of Sullivan's apartment emphasizes the clinical, cold nature of the hit. It signifies that the law, or at least a representative of it, has finally caught up to Sullivan using the same cold-blooded tactics Sullivan used against others.

Who Killed Sullivan and Why?

The killer is Staff Sergeant Sean Dignam, the former second-in-command of the Special Investigations Unit.

The Motivation for the Hit

Dignam’s motivation is rooted in a mix of professional duty and personal vengeance. Throughout the film, Dignam is the only character who consistently suspects Sullivan of being a mole. Unlike Captain Queenan, who was more diplomatic, Dignam was openly hostile toward Sullivan from the beginning.

After Captain Queenan is murdered and Billy Costigan is killed, Dignam is forced into "resignation" or leave. However, he remains the only person alive who knows the full scope of the tragedy and Sullivan’s likely involvement. Because Sullivan had effectively "won" legally, Dignam took it upon himself to deliver "street justice."

The Enigma of Dignam’s Evidence

A common question remains: How did Dignam know for sure? While the film doesn't explicitly show it, it is heavily implied that Madolyn Madden (Sullivan’s fiancé) provided the catalyst. At the end of the film, Madolyn receives the incriminating recordings that Costigan sent to Sullivan. Her presence at Costigan’s funeral, and her refusal to speak to Sullivan afterward, suggests she likely passed information or keys to Dignam, or at the very least, her departure left Sullivan vulnerable.

Symbolism at the End: The Rat on the Railing

As the camera pans away from Sullivan’s dead body, it moves toward the window, showing a rat scurrying across the balcony railing with the Massachusetts State House in the background.

Disambiguation: Other "Sullivans" in Military/Action Media

While the most famous "Sullivan" death involving "boots" is from The Departed, the query sometimes overlaps with other media where characters named Sullivan meet tragic ends in a "boots on the ground" context.

Sergeant Tom Sullivan (Call of Duty: World at War)

In the world of gaming, particularly in the "Boots on the Ground" genre of military shooters, Sergeant Tom Sullivan is a major character in Call of Duty: World at War.

• What happens to him: Sullivan is the squad leader of the American campaign.
• How he dies: At the end of the mission "Little Resistance," after successfully calling in a rocket strike on Peleliu, Sullivan is suddenly attacked by a Japanese banzai soldier. He is stabbed with a katana and dies in the arms of the player character, Miller.
• Why the confusion: Many players refer to these older COD titles as "the boots games" (referring to the classic infantry combat). Sullivan's death is a scripted, unavoidable event that shocks players early in the story.

Cassie Sullivan (The 5th Wave)

In the literary and film series The 5th Wave, the protagonist is Cassie Sullivan.

• What happens to her: In the final book of the trilogy, The Last Star, Cassie Sullivan sacrifices her life. She realizes that the only way to stop the alien "Others" is to destroy their ship while she is still on it.
• The End: She dies to save humanity, including her brother Sammy (nicknamed "Bean").

Technical Depth: The Execution Scene in The Departed

The ending of The Departed was a departure from its source material, the Hong Kong film Infernal Affairs. In the original version, the Sullivan-equivalent (Lau Kin-ming) survives, though he is trapped in a mental hell of his own making. Scorsese opted for a more visceral, final conclusion.

The Choice of Weapon

Dignam uses a suppressed .22 caliber or similar small-frame pistol. This choice is deliberate. A suppressed weapon allows the hit to remain quiet in a luxury apartment building where neighbors would immediately report a loud gunshot. The "Okay" delivered by Sullivan suggests a realization of the poetic justice at play; he had lived by the sword (and the lie) and was now dying by it.

Forensic Logic of the "Booties"

In 2026, forensic science has evolved, but the principle of the "surgical bootie" remains a staple of crime scene management and, ironically, professional hits. By wearing the plastic covers, Dignam ensured that:

1. Gait Analysis: While modern CCTV can sometimes identify people by their gait, avoiding specific shoe-print patterns remains a priority for avoiding detection.
2. Trace Evidence: He avoided bringing outside soil or debris into the apartment and avoided taking Sullivan’s blood back out on his shoes.
3. DNA: The full-body coverage (tracksuit and booties) minimized the shedding of hair or skin cells.

Common Misconceptions About Sullivan's Death

There are several theories and misconceptions regarding the final scene that have persisted for years.

1. "Sullivan committed suicide"

Some viewers misinterpret the quickness of the scene. Sullivan did not kill himself. He was executed by Dignam. His "Okay" was a moment of resignation, not an invitation.

2. "The guy in the boots was Billy Costigan's ghost"

This is a purely supernatural theory with no basis in the film's gritty realism. The character is clearly identified as Dignam by his facial features and his previous established hatred for Sullivan.

3. "Sullivan survives in a post-credits scene"

There is no version of The Departed where Sullivan survives. His death is the definitive closing statement on the cycle of violence depicted in the movie.

Frequently Asked Questions

Did Colin Sullivan know Dignam was going to kill him?

Sullivan did not know specifically that Dignam was in his apartment, but the moment he saw him, he understood why he was there. His lack of struggle and his final word, "Okay," indicate that he knew his double life had finally caught up with him and that he had no more moves left to play.

Why did Dignam wait until the end of the movie?

Dignam likely waited for the legal dust to settle. By waiting until after Costigan’s funeral, he ensured that Sullivan felt a false sense of security. Additionally, it took time for the evidence (the tapes) to reach the right people, which likely gave Dignam the confirmation or the "access" he needed to move forward with the hit.

Is the "Boots" character a different person?

No. The person wearing the plastic booties is Sean Dignam. The term "boots" is simply a common descriptor used by fans to describe the specific look of the killer in the final scene, as the plastic covers are very prominent in the low-angle shots.

What happened to the money Sullivan made?

After Sullivan’s death, his assets would likely have been seized by the state. Since he was a high-ranking police officer found dead in a suspicious manner, a full investigation into his finances would have followed, eventually revealing the ties to Frank Costello that he had tried so hard to hide.

Is there a sequel where Sullivan's death is explained?

No. The Departed is a standalone film. While there were rumors of a sequel focusing on Dignam (the survivor), it never materialized. The story is considered complete with the death of the primary "moles."

Final Actionable Summary for Fans

If you are looking to revisit the scene or understand the deeper lore:

• Watch for the Tapes: Pay close attention to the scene where Madolyn listens to the tapes. Her reaction is the true "death sentence" for Sullivan.
• Observe Dignam’s Departure: After Dignam leaves the SIU, he disappears from the film until the final scene. This gap is when he is presumably planning the assassination.
• Check the Symbolism: Notice how many times "rats" or references to snitching appear before the final shot of the actual rat.