Does anyone know, or anyone have a good guess, as to the time span the movie covers, from when Leonardo Dicaprio first goes undercover, till when he is killed? I tried figuring it out, but a lot of things confuse me. I would assume it would be a good while, since Matt Damon and Vera Fermiga meet, move in together, and get pregnant in the time span. While meeting under the bridge DiCaprio tells Martin Sheen and Mark Wahlberg that he has been at it for a year now, but then at the end DiCaprio tells Matt Damon that his only contact for the last nine months has been a police shrink. Any idea for how long he was under cover?

When Matt Damon is ambushed by Mark Wahlberg in the end of the movie, just before Mark shoots him he says "Okay". Does this mean "Okay, shoot me" or "Okay, I admit it"? [I took it to mean "Okay [I know why you're here]."] Answered by Phixius

What exactly was in the envelope that Costigan hands to the therapist? Was it the tapes that Frank had recorded of himself? [That, and other evidence of Matt Damon's guilt.] Answered by pross79

In the final shot of the film, is it really Matt Damon lying there on the floor, or a body double? Nobody else has noticed, but something just doesn't seem right. It looks like the hair is darker/cut differently, and the facial features don't feel right. [I've had a good look and, to be honest, it just looks like Matt Damon to me. He's got his face pressed against the floor, which is always going to make it look a little distorted - it's not a particularly natural way to lie. Hair colour looks right - if anything, it looks a little lighter than the shot immediately before he's killed, something readily explained by lighting. In the end, given that the face is visible, there's no way they'd use a body double, nor is there any reason to do so.] Answered by Tailkinker

What is the tune that is playing when we first see Billy going into jail? [It is called "Shipping Up to Boston" by the band The Dropkick Murphys, from their "Warrior's Code" album.] Answered by Vin15Nets

There was one thing I wasn't really sure on, and I don't even know if there is a definitive answer. Did Mark Wahlberg kill Matt Damon because he figured out that Matt Damon's charecter was working with Frank and he had killed all those cops, or did he just kill him for revenge over the way Matt Damon treated Wahlberg when he took over his job? [The assumption is that Wahlberg learned of Damon's betrayal from the envelope given to Vera Farmiga, Damon's therapist girlfriend. It could also have been for revenge, but Wahlberg did know that Damon was the rat when he killed him.] Answered by Dandude