Our good friends over at Taxpayers Against Fraud have made this handy video to explain what you should do to prepare to bring a case under the False Claims Act. In a nutshell, it suggests that you organize your best evidence and write a detailed narrative of who you are, what the fraud is, how you discovered it, and what proof you have to support your claims.
Most importantly, the video suggests that you contact a False Claims Act lawyer to advise you. And the earlier the better! With proper counsel, you can build your case by collecting the best evidence (which is often not what you expect) and help you trigger the protections offered by the anti-retaliation component of the statute. If you wait until after you are terminated or quit and no longer have access to files, your case is likely to be much weaker, or you may not have enough to bring a case at all!