Well, for one thing, he has no idea what the requirements are to make a prima facie case for defamation. Like, at all.
Defamation and other "accounts?"
For another, this is likely an employment-at-will contract so they can pretty much fire his ass for whatever reason (even though there is cause here) as long as its not based on race or the like.
Oh, and then theres the fact the D.A. is the one that files the criminal complaint. (True, D.A.'s are lawyers, but its not the victim's counsel that decides if charges are pressed which is what seems to be implied).