We need a national civilian oversight department that handles all police and sheriff department internal investigations. You can even base it off of something already existing, NCIS. Their system works just fine with civilians and non-military investigators even able to handle classified issues, something regular police wouldn’t even have to worry about. And outside investigators means local corruption isn’t an influence.

Which is of course why it will never happen. Can’t actually hold those with any little bit of power responsible, even a random beat cop.