Yes, I love Nightline. They've focused on this story all week.

Basically there was a study done in the early 1970s that dealt with the psychology of prisons. The authors of the study took subjects and divided them into "guards" and "prisoners". Over a week's time, they noticed that the guards kept ratcheting up what they would do to the prisoners to demonstrate the guards' power. I believe the experiment was meant to last longer than a week, but it was disbanded because of what the researchers saw in terms of escalation.