I've previously commented on Phillips Zimbardo's thoroughly engaging work, including his lecture on "The Secret Powers of Time."  He is well respected for his research on a wide variety of social psychology issues. Forty years ago, Zimbardo unwittingly served as the mastermind of the infamous "Stanford prison experiment."  He selected healthy young men with no history of any psychological problems, drug abuse or violence and he put them into a situation where they would fill the roles of prisoners and guards in a simulated prison (in a school building) that soon turned ugly as Zimbardo stood by and observed. The prisoner abuse eventually become intolerable. During the course of the experiment, the "guards" became physically and emotionally abusive toward the "prisoners." Zimbardo took a lot of criticism for running this experiment, even though he shut it down six days after beginning what was scheduled to be a two-week long experiment. Zimbardo still today notes that his own "passive role" enabled the abuse. The Stanford experiment clearly demonstrated that a toxic situation can cause "good" people to act grotesquely. Based on his previous work, including the Stanford experiment, Zimbardo was called to serve as an expert witness in a case the US government brought against an Abu Ghraib guard who was accused of being a "bad apple." Zimbardo disagreed with that characterization, opining that Abu Ghraib was a terrible situation that was likely to corrupt many good people. As indicated in an article by Greg Miller titled "Using the Psychology of Evil to Do Good" in the April 29, 2011 edition of Science (available online only to subscribers), the guard being prosecuted:

. . . soon found himself supervising about a dozen military police and dozens more Iraqi police responsible for guarding more than 1000 Iraqi prisoners at Abu Ghraib. The prisoner population had recently tripled, creating a chaotic environment in which standard procedures and oversight broke down. The language barrier made prisoner same anonymous, Zimbardo says, and many prisoners were forced to go naked, further dehumanizing them and creating a sexually charged atmosphere. Guards worked daily 12 hour shifts for weeks on end. Fear of a revolt-or an attack from outside-mixed with boredom and exhaustion to create a volatile brew.

In short, Abu Ghraib constituted an episode of déjà vu for Zimbardo. It was no surprise to him that guards with no history of troublemaking or bad character would engage in grotesque acts.