The movie Shoah. It as a documentary about the Holocaust that is about >9 hrs long and it is, if I recall, all interviews with people who committed the atrocities of WW II (not the more common witness of victims) or the people who watched it but did nothing. It shows that our naive belief that atrocities are committed by some form of special monsters is wholly untrue. Awful, unspeakable acts are committed by everyday, regular people who simply go along with whatever they get swept up in. It also shows how every generation of (what came to be called) war criminals justifies their atrocities with the idea that "well this time it is different". And it shows that it can happen "here", wherever "here" is.