Broken Windows And Broken Police Forces
Broken Windows theory comes out of a James Q. Wilson and George L. Kelling article in The Atlantic from March of 1982. In a nutshell:

Second, at the community level, disorder and crime are usually inextricably linked, in a kind of developmental sequence. Social psychologists and police officers tend to agree that if a window in a building is broken and is left unrepaired, all the rest of the windows will soon be broken. This is as true in nice neighborhoods as in rundown ones.

...Consider a building with a few broken windows. If the windows are not repaired, the tendency is for vandals to break a few more windows. Eventually, they may even break into the building, and if it's unoccupied, perhaps become squatters or light fires inside.

Or consider a pavement. Some litter accumulates. Soon, more litter accumulates. Eventually, people even start leaving bags of refuse from take-out restaurants there or even break into cars.

Ken White at Popehat lays the two side by side:

If tolerating broken windows leads to more broken windows and escalating crime, what impact does tolerating police misconduct have?

Under the Broken Windows Theory, what impact could it have but to signal to all police that scorn for rights, unjustified violence, and discrimination are acceptable norms? Under Broken Windows Theory, what could be the result but more scorn, more violence, and more discrimination?

Apparently we've decided that we won't tolerate broken windows any more. But we haven't found the fortitude to do something about broken people. To put it plainly: just as neighborhood thugs could once break windows with impunity, police officers can generally kill with impunity.