I'd say you are wrong. Why the sudden investigation right after he testifies for the defense in the Chauvin trial? The guy is retired from that position. The the scope of the investigation is all cases involving him. In other words, they don't have any specific evidence of a problem in a specific case. That indicates it's a 'fishing expedition.' That is, they are hoping to find something somewhere in this guy's case history to smear and discredit him with.
All that says politically motivated.
He showed who he is at this trial. He was way off. His testimony was crap. It is logical to see if he was as bad at other trials. His weirdness may have put innocent people in jail.