A police cleanup crew arrives, and Colin gives his account of how Billy Costigan and the other officers all died. He mentions that Billy was an undercover cop, so Billy ends up getting a state funeral.
Madolyn goes to the funeral and cries for Billy. Then she stares at Colin with accusing eyes and walks past him without a word when the funeral is over.
Colin heads back to his apartment alone and finds Dignam inside wearing plastic on his feet and all over his body.
Dignam shoots Colin through the head and walks away without a trace.
In the final shot of the movie, we get a look at the balcony railing outside Colin's apartment. And what do we see walking across it but a rat. Some might call it a… cheesy ending.
All right, all right. We'll take that last one back.