This is one of the most difficult stories I’ve edited in a long time: How Good People Turn Evil, From Stanford to Abu Ghraib.

Kim Zetter did the interview with Philip Zimbardo, a psychologist who is famous/notorious for his 1971 “Stanford prison experiment,” a psychology study in which some students were assigned to play “prison guards” and others “prisoners.” The experiment quickly spiraled out of control, with the prison guards — and Zimbardo himself — becoming increasingly detached from any moral compass, forcing the prisoners to strip, perform humiliating sexual acts, and the like.

Thirty years later, a similar dynamic — with much more horrifying effects — was happening at Abu Ghraib.

Zimbardo thinks that almost anyone can succumb to these kind of “evil” actions, given the right circumstances and social pressure. Evil is his word, and perhaps its too loaded with religious connotations — but regardless of your point of view, such behavior is certainly horrifying. Zimbardo tries to explain why it happens without excusing people from moral responsibility for it. On the other hand, he also testified for the defense of one of the Abu Ghraib prison guards, and it’s in that capacity that he got copies of many photos from the prison.

Zimbardo plans to show these images as part of his presentation at the 2008 TED conference in Monterey. Although many photos from Abu Ghraib have already been published, some of the images Zimbardo is showing appear to be previously unpublished, which is why we made the decision to publish them alonside his interview.

The photos (and the video slideshow Zimbardo made of them) are very disturbing, and I don’t recommend looking at them. But I do recommend reading the accompanying interview, for its insight into just how badly people can behave — and what it takes to make a stand against evil.