My thinking is that if you're sitting on information about who did it, say if you're a girlfriend or something, it may bother your conscience nightly, but there's really no pressure to make a decision one way or another when the case is this cold.
However, once Payne starts digging around, and all the renewed interest, I have to imagine it makes you feel a little squirrely knowing they might eventually get on the right trail. And if they do...you have to be concerned about what happens when they find out you know. You might end up an accomplice after the fact, but at the very least, you're going to have to answer a lot of questions about why you didn't say anything.
While Payne never dialed in on the killer, I think there's a strong chance that his presence pressured someone to talk about what they knew and get ahead of things.
