I imagine the investigator is an at will employee, but I would see a lawyer anyway.
Could be he has legal recourse for a wrongful termination.
There is no law saying you have to tip a waiter. If you tell them why you are actually doing them a favor.
Washington Attorney General Bob Ferguson likes to sue the Trump administration. Hes done it now a total of 80 times a rate of nearly once every other week since Donald Trump took office.