Agree with Ellexoh, and others ... the problem with getting at the truth with these guys, is they're only going to tell as much of the truth as they've acknowledged to themselves. And frequently they've had plenty of practice lying to themselves.
They also tend to confess just a little bit at a time. There's a very funny "Friends" episode where Phoebe starts talking about the difference between what people say, vs. what they really mean. As an example, she says when a guy says "I think we should start seeing other people" what he really means is "I already am." And this is funny because it's true and painful.
So if the idea is to get at the truth, start by understanding that you're not going to hear it from him. Learn what he looks like when he's lying -- when you KNOW he's lying, just let him keep going.