I would not hesitate to report him immediately, you were doing your job and if you turn him in, there will be no reprisals toward you. If, however, you choose to wait until he gets caught through other means, you may very well be brought down with him. The key is to disassociate yourself with him as soon as possible, by that I mean quit. you can do this before or after you report him, just don't let him fire you, or it may look like more of a disgruntled employee case.