[ Jack nods slowly, digesting the information as it comes in piecemeal form. He has to assume everything he's being told is not just because Costigan is feeling in an overly indulgent mood for sharing his life so is important, to be committed to memory even if it's not to be shared. ]

Can I ask why?

[ Then he realizes that's too vague and clarifies: ]

I mean, not back in Boston but here. There wasn't any need for you to go around doing that in a strange city where no one else knew you, right? You didn't have to be a cop, but you didn't have to fall in with criminals either. You could have just been yourself and no one would have been the wiser.

So this was something you... wanted to do?

[ There's no judgment in either his expression or his tone... not just openly, but at all. Jack really is just listening at this point, trying to understand where this is coming from and where it's going. ]