I suggest you not say anything more to him about it. I'm with you in that I would not want to be the guy to turn him in. But coming down on him is just going to convince him that the next time he should just keep quiet.

Maybe if he keeps running his mouth about it, he'll brag to someone who will turn him in.

I'm a guy who supports abiding by the game laws even if you don't agree with 'em. That makes it fair for all of us.