Being busy is no excuse. We're all busy but everyone has at least 10 mins to send an email. It's all about what the priority is.
That said, you should cover yourself by asking for copies of all his conversations with CP. Tell him you think it'll add to the weight of the case if you get involved too, and that it'll help validate your claim if you show proof that it is in fact CP's issue.
Handle the issue maturely and like a gentleman - no need to accuse anyone just yet - but call his bluff. If he stonewalls you on that, you can be sure he's trying to screw you over. Sorry to be blunt. Keep pursuing the issue since it's a large amount of money we're talking about. If it gets ugly, threaten him with getting the law involved. Usually that motivates people pretty quickly. The police and detectives are paid to help with matters like this and since there's electronic footprints of your interactions with him, gathering "proof" won't be very hard.
that's my advice
Here we are again bro -just you and me. Same kind of moon same kind of jungle. Real number 10 remember? Whole platoon, 32 men chopped into meat... We walk out just you and me, nobody else. Right on top huh? Not a scratch... Not a fuckin' scratch... - Sgt.Mac, Predator