Can't provide sources because obviously it's anecdotal evidence but from personal experience it tends to be the young post military punks that are the worst.
http://www.copblock.org/1504/policebad/
How to get away with murder or assault as a cop:
Step one: find someone to beat or murder preferably black
Make sure you are just out of sight of the dash cam
Don't worry if there are witnesses unless they're recording and then confiscate their cameras
Make sure the dash cam voice recording is removed or altered
Step two: write on your police report that they had a weapon or posed a threat to your life so your beating a murder justified it doesn't matter if this is false they will believe your word no matter what because you're a cop who spent like a year in police academy and did some push ups and studied for tests this somehow makes you more believable then the common delinquent.
If people try speaking up about this simply offer them money or just ignore them because they'll become old news and just go away anyway .
If the public outrage become significant just take a leave without pay which is actually great! no work, same pay, whatever I'll probably never face jail time anyway
If it becomes a nation wide out rage just remember that Republican white people will make T-shirts for you and start a run fundraiser for you so you'll make a ton of money from beating someone!
If you have to go to court just remembered have your defense attorney point out how much of a criminal or scumbag that your victim was have them completely smashed their character and use photos that seem incriminating from their social media accounts
Step 3: enjoy
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If we're going by personal experience I have met one cop who wasn't a complete asshole and it was the one I mentioned previously. I've been detained in front of my own house because it was a couple of minutes after curfew for over and hour. Or the time my dad was at a casino drinking and was asked to stop so he sat at the bar and asked for water and he was thrown to the floor because a cop but he was still drinking and then started yelling at him to stop resisting even though he was on his stomach spcompletely still and then tased him and somehow the security footage somehow got wiped but the audio didn't so in court all you heard was "STOP RESISTING STOP RESISTING " *crackling sound*. I've had a few traffic stops and one accident and plenty of check points and they love treating you like dirt. It doesnt matter if you're cooperative and polite theyve treated me like the scum of the earth. I believe cops can be good people but I will probably always hate police along with millions of other people and you can say "B-BUT THERES GOOD ONES" until you're blue in the face but you'll prob never change my mind.