I am looking for a verb to describe the action of a good guy becoming a bad guy. There is a word for it in my mother language, but I am not sure if there is a word for it in English.
The verb, which could be literally translated as 'become bad, turned into a bad guy'. an example would be:
He used to be a good cop, but now he___, mingles with the gangsta on the street, sad thing.
update: thanks everyone for your answers and comments. it seems a word to describe this behavior of people working in law enforcement is unanimous, but a word to describe this behavior that includes ordinary folk seems remains controversial.