People wildly underestimate the rate at which cops commit crimes. Not just murder, which deservedly gets the lions share of the publics attention - drugs, theft, extortion, sex-trafficking, if you can think of a crime, there is probably a cop in your community who's done it.
The top narcotics squad for Brooklyn was robbing people and running a prostitution ring (I'm amazed they got busted). The city LITERALLY PUT UP ADS TELLING COPS NOT TO ROB PEOPLE OR ACCEPT BRIBES. This was ~2 years ago.
@Expecting_Words Five words: Baltimore Gun Trace Task Force.
@Expecting_Words When I lived in the UK, the Metropolitan Police Force (London's police) were riddled with corruption.
An investigation named Operation Countryman was launched. The Met senior leaders obstructed it at every twist and turn. My ex father-in-law was an officer from Sussex who was part of the Countryman team, and he received unsubtle death threats and took early retirement.
After a while, lots of senior officers in the Met began taking early retirement on medical grounds.
@Expecting_Words Add domestic violence to the laundry list.
Police forces get their recruits disproportionately from two sources: (1) the military (which is a bad idea, as Radley Balko explains in his book), (2) the would-be-tyrants and authoritarians.
It is not at all surprising that abuse of power is rampant in some police forces.