In this situation, yes, I would rat the guy out.
Not only does he apparently have a problem with not owning up to his own actions, but if I were the victim in this, I'd want some closure, and more importantly, some compensation from the asshole who did that to my car. He needs to get some punishment for his actions.
On the topic of ratting out, though- I would say that I would rat friends out if they were breaking the law and getting people hurt. Its hard to do, but its better than just letting it go on. For instance, I met a guy in classes at University, got along well with him and overall liked the guy- but then I caught him with a vial of GHB one day and wasn't gonna wait to find out what he was gonna do with it, especially when there was a rape on campus some time prior to that- so yea, I ratted the guy out. He was arrested, and hated me- probably still does.