I don't mean "how" in terms of "how do I know the right thing to do", more a question of what, exactly, is the best way to do the ethical thing without getting burned.
Is it better to take the hush money and pretend to be satisfied, then whistle-blow to the FBI once your corrupt boss thinks you're happy? What kind of evidence would you need in order to convince an FBI agent, in a phone conversation, that you are calling in a real crime and not just a prank? If your law-enforcement contact asks you to wear a wire to work and have a leading conversation with your boss, should you do it? What kind of corporate espionage do you perform to make sure a corrupt business does not shred or cover up evidence?
Maybe I've been seeing too many spy movies recently, but I find myself fascinated by questions like that.
There's lots of hacker literature about what to do when you're an employee in the middle of an unsuccessful company, and some about what to do when you are attempting to catch a cracker or other computer saboteur on your network, but I don't think I've ever seen a story or essay on the subject of what to do when your company is not merely clueless but literally criminal.