"Wir haben es nicht gewusst" is what the Germans used after WW2, but part of me can believe it because the world wasn't as connected as it is today.
Today though? It does not fly. People know about it, and if they are not actively participating in stopping it, they are complicit - "not my problem, I don't care, blue/all lives matter, what about these crime statistics, muh freedom", these are all people that know about it but do not care, or they do care but they're on the wrong side.
See police brutality, me too, etc.