After living in Europe for six years now, my wife is still puzzled sometimes by the differences between Europe and North-America when it comes to the police: how they are experienced by the population and how they see and present themselves and which role they think they're playing in society. Big difference. I'm certainly over-generalizing but here, we see cops as approachable and helpful in general (with exceptions) while in North-America, at least my wife's impression is that of cops being mostly intimidating (again, with exceptions).
Of course, this is all complex and different social and societal aspects play a big role, such as e.g., the odds for a cop of running into an armed person. But when I read how the police handled the situation with the group of black trick-or-treaters, it seems so foreign to me now from a more European perspective.
I suppose accountability is always going to be an issue - who watches the watchmen? But it should not be - in a democracy especially, there should be functioning mechanism to prevent abuse of power, and that of course applies to police actions, too.
...how could this be justifiable?