chum is right. His acttion (or inaction) is due as much, if not more, to the situational factors vs. personality factors. Milgram's study is just one of many on the subject.
"Ordinary people, simply doing their jobs, and without any particular hostility on their part, can become agents in a terrible destructive process. Moreover, even when the destructive effects of their work become patently clear, and they are asked to carry out actions incompatible with fundamental standards of morality, relatively few people have the resources needed to resist authority" (Milgram, 1974).
