Prosecute the police that arrested him for running a criminal enterprise.
I'd say give the cops a break, they did there job. One man hit another, what are the cops supposed to do, just take one guys word for why?
If I walked up and slugged somone and made up a good reason, the cop would still arrest me, at least to verify the truth.
DOn't forget, once he's arrested, he gets the right to remain silent and a laywer, hence instead of just holding him and having him incriminate himself.
DOn't prosecute him, but you have to arrest him to at least verify that he's telling the truth, to quote Reagan "trust but verify".