I've been trying to compose a response to this, describing a similar situation I was involved with. I just can't do it without saying more than is prudent. I was slow to catch on to what was going on but I did the right thing when I did and the guilty weren't punished. I don't mind talking more about it privately. The lesson I learned was that there are a lot of good, honest, and competent people around but there a few who aren't and I wish I hadn't wasted time and frustration with people who were willing to put up with that corrupt few. You've got a tough problem but it sounds like you have good judgment. I hope it works out well for you.