If it's local, report it to the state, if it's the state report it to the feds, if it's the feds your only real option is to do it and run to another country, or keep your mouth shut and just find a new job. This process has repeated itself many times in the news if you research it.
In theory that is how it should work. I promise in practice that you will get absolutely nowhere. Most prosecutors seem local, either municipal or county, but in actuality are State workers, and the State is generally completely disinterested in investigating its own staff.
The feds are even less interested in investigating matters that should be handled by the State.
I say this from practical experience of trying to move the State Attorney General's office and the FBI to investigate and getting absolutely nowhere at all.
My next plan is to simply take a local friendly reporter with a video camera and perform a sit-in at the prosecutors office until they promise to do something or they have me arrested for trespass.
