Yeah, feature length movies will show "bad cops" on screen for a few minutes, but the ongoing series tend to shy away from anything other that wholesome upstanding proud law men and women keeping the world safe from itself.

I used to live in a neighborhood with a lot of police residents. Most of them are "good" in their own actions all of the time. All the ones I knew were "good" in their actions most of the time, but once in a while they'd go all judge-jury-and-executioner with a badge and a gun - I never knew about any coverups, but I did have a neighbor get suspended for a month with pay and a strong word from his sergeant "don't to that again..." The worst of it is that virtually ALL of them will look the other way / assist in spinning an issue to "help a brother in blue out of a jam," and they know that they have each others' backs that way, so they will do bad things because they have that confidence that they are untouchable.