There are two antithetical ways in which one can approach the explanation of the Holocaust. One can consider the horrors of mass murder as evidence of the fragility of civilization, or one can see them as evidence of its awesome potential. One can argue that, with criminals in control, civilized rules of behaviour may be suspended, and thus the eternal beast always hiding just beneath the skin of the socially drilled being may break free. Alternatively, one can argue that, once armed with the sophisticated technical and conceptual products of modern civilization, men can do things their nature would otherwise prevent them from doing. To put it differently; one can, following the Hobbesian tradition, conclude that the inhuman pre-social state has not yet been fully eradicated, all civilizing efforts notwithstanding. Or one can, on the contrary, insist that the civilizing process has succeeded in substituting artificial and flexible patterns of human conduct for natural drives, and hence made possible a scale of unhumanity and destruction which had remained inconceivable as long as natural predispositions guided human action.That's from Zygmunt Bauman's Modernity and the Holocaust. Bauman goes on to say that he opts for the second approach, and his book is a powerful and illuminating statement of it. But I don't think we are obliged to treat these two styles of explanation as mutually exclusive. Everything Bauman says about the destructive potential of modernity, and about the patterns of thought and organization it contains which support that potential, are compatible with holding that there are also cruel, blind and destructive human impulses which play their own role in the periodic production of catastrophe.
From one study:
The commandant of the Riga ghetto, Karl Wilhelm Krause[,] who was known to personally shoot inmates, held strikingly generous views about child care... An example of his perversity can be seen in his permitting the construction of a rudimentary playground in close proximity of the gallows. After executions, the commandant was often seen to go to the sandbox and give chocolates and candy to the playing children; he liked to be called "Uncle Kraus."From another:
During the summer and fall of 1942, several hundred thousand Jews were massacred in the Volhynian-Podolian region... The shooting site was on a hill about two miles away, and [a] mother, carrying [her] child, was forced to run this distance after a truck already filled with victims. Standing near the dug-out half-filled with bodies, the child said: "Mother, why are we waiting, let us run!" Some of the people who attempted to escape were caught immediately and shot on the spot. The mother stood there facing the grave. A German walked up to the woman and asked: "Whom shall I shoot first?" When she did not answer, he tore her daughter from her hands. The child cried out and was killed.