Surveillance Guy: Who the fuck are you?
Dignam: I'm the guy who does his job. You must be the other guy.
Ellerby: You have an immaculate record. Some guys don't trust an immaculate record. I do. I have an immaculate record.
Colin Sullivan: What Freud said about the Irish is, we're the only people who are impervious to psychoanalysis.
Colin Sullivan: If we're not gonna make it, it's gotta be you that gets out, cause I'm not capable. I'm fucking Irish, I'll deal with something being wrong for the rest of my life.
Oliver Queenan: Do you know what we do here? My section?
Billy Costigan: Sir, yes, sir. I have an idea...
Dignam: Whoa, whoa, whoa. Let's say you have no idea and leave it at that, okay? No idea. Zip. None. If you had an idea of what we do, we would not be good at what we do, now would we? We would be cunts. Are you calling us cunts?
Oliver Queenan: Staff Sergeant Dignam has a style of his own. I'm afraid we all have to get used to it.
Dignam: My people are out there. They're like fuckin' Indians. You're not gonna see 'em you're not gonna hear about 'em except from me or Captain Queenan. You will not ever know the identity of undercover people. Unfortunately, this shithole has more fuckin' leaks than the Iraqi Navy.
Ellerby: Fuck yourself.
Dignam: I'm tired from fuckin' your wife.
Ellerby: How's your mother?
Dignam: Good, she's tired from fuckin' my father.
Madolyn: Why is the last patient of the day always the hardest?
Billy Costigan: Because you're tired and you don't give a shit. It's not supernatural.
Dignam: My theory on Feds is that they're like mushrooms, feed 'em shit and keep 'em in the dark.
Frank Costello: How's your mother?
Man: Oh... I'm afraid she's on her way out.
Frank Costello: We all are. Act accordingly.
Lazio: Without asking too many questions, do you have anyone in with Costello presently?
Dignam: Maybe. Maybe not. Maybe fuck yourself.
Ellerby: I'm gonna go have a smoke right now. You want a smoke? You don't smoke, do ya, right? What are ya, one of those fitness freaks, huh? Go fuck yourself.
Colin Sullivan: I'm going to need the identity of your undercovers.
Dignam: Blow me, all right? But not literally, though. Unfortunately, there's no promotion involved for you.
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.