How would you react if you found a coworker on the sex-offender registry?

Basically the situation I'm in. Guy's been there since before I started, known him for six years, and I've hung out with him outside of work. But my girlfriend's screwing around on the registry and sees his name on there. Sure enough it's him. Says he was with a minor female, but it happened quite a while ago (back in 1992), so he must have been pretty young when it happened. Anyway I don't think people at work know about this. So I'm left wondering if I should oust him as a pervert, or let it slide since it was like forever ago and maybe there's a story behind the situation... I don't know. Tell me what you'd do?