Ok so, we all agree that there is "something there" but (1) how do I approach that and (2) how do I deal with it
I know, both questions only I can answer
I would calmly continue to insist on total transparency. Get your C involved. Most likely, if there is something, it will come out then. He needs to be accountable. As to what you'll do with whatever you find out ... we'll cross that bridge when we know if there actually is anything. Hang in there. You're doing well.