WIRED features an interesting interview with psychologist Philip Zimbardo who conducted the famous Stanford Prison Experiment. He links his research to actual events like Abu Ghraib or jewish wardens in nazi concentration camps.
Read "How Good People Turn Evil, From Stanford to Abu Ghraib" over at WIRED.
The Stanford prison experiment was a psychological study of human responses to captivity and its behavioral effects on both authorities and inmates in prison. [...]from wikipedia
Undergraduate volunteers played the roles of both guards and prisoners living in a mock prison in the basement of the Stanford psychology building.
Prisoners and guards rapidly adapted to their roles, stepping beyond the boundaries of what had been predicted and leading to dangerous and psychologically damaging situations. One-third of the guards were judged to have exhibited "genuine" sadistic tendencies, while many prisoners were emotionally traumatized and two had to be removed from the experiment early.
Finally, Zimbardo, alarmed at the increasingly abusive anti-social behavior from his subjects, terminated the entire experiment early.