One caveat to this: from the data I've seen a lot of these issues revolve around specific communities. Please keep in mind that police forces are not national, but rather local.
The bad cop stereotype is universal. But America's current police culture in my opinion encourages bad cop behavior. The culture is way too military-oriented versus community oriented at the moment. It is hard to "protect and serve" your community if you are always at "war" with some "enemy". This case is a perfect example of that.
It seems to me like the most outrageous police brutality sources would be solved by high-level oversight.