"Monsters exist, but they are too few in number to be truly dangerous. More dangerous are the common men, the functionaries ready to believe and to act without asking questions." Primo Levi's words disclose a chilling truth: assigning blame to hideous political leaders, such as Hitler, Himmler, and Heydrich, is necessary but not sufficient to explain how the Holocaust could have happened. These leaders, in fact, relied on many thousands of ordinary men and women who made the Nazi machine work on a daily basis--members of the killing squads, guards accompanying the trains to the extermination...