That’s a good question.
You know how all the people taking part in a robbery get charged with murder if just one of them kills someone?
I’d view it like that. A cop that covers up corruption for a partner is guilty of corruption. A cop that covers up a DUI carries a similar amount of guilt.
A cop that exercises ‘professional courtesy’ to overlook a minor traffic violation? Same negligible amount of guilt.
I think it seems about right.