In 1971, psychology professor Philip Zimbardo created the Stanford Prison Experiment in which 24 college students were randomly assigned the roles of prison guards and prisoners at a makeshift jail on campus. The experiment was scheduled to run for two weeks. By Day Two, the guards were going far beyond just keeping the prisoners behind bars. In scenes eerily similar to Abu Ghraib, prisoners were stripped naked, bags put on their heads and sexually humiliated. The two-week experiment had to be canceled after just six days. Zimbardo tells the full story of the landmark study in his new book, "The Lucifer Effect." [rush transcript included]

More information at www.lucifereffect.com

As the United States enters the fifth year of its occupation of Iraq, some of the most enduring images of the war remain the vivid photographs of US soldiers torturing Iraqi prisoners at Abu Ghraib.

The pictures were leaked to the press and first revealed to the world in May 2004. Images showed Iraqis with bags over their heads, beaten, set upon by dogs and forced into sexually humiliating acts. The Bush administration tried to paint the scandal as an isolated incident committed by rogue soldiers. But who is really to blame for the abuses at Abu Ghraib? The answer may lie in a landmark study conducted more than three decades ago.

In 1971, psychology professor Philip Zimbardo created an experiment at Stanford University in which 24 male college students were randomly assigned the roles of prison guards and prisoners at a makeshift jail on campus. The experiment was scheduled to run for two weeks. By Day Two, the guards were going far beyond keeping the prisoners behind bars. In scenes eerily similar to Abu Ghraib, prisoners were stripped naked, bags put on their heads and sexually humiliated. The guards had become dangerously sadistic and the prisoners were breaking down emotionally. The two-week experiment had to be canceled after just six days.

Professor Philip Zimbardo has just written a new book that, for the first time, tells the full story of the famed Stanford Prison Experiment. It's called "The Lucifer Effect: Understanding How Good People Turn Evil." Professor Zimbardo joins me today from our firehouse studio in New York.

• Philip Zimbardo, creator of the landmark Stanford Prison Experiment. He is professor emeritus of psychology at Stanford University. Zimbardo is the author of the best-selling introductory psychology textbook, "Psychology and Life" as well as "Shyness." He recently served as the president of the American Psychological Association and is now director of the new Center for Interdisciplinary Policy Education and Research on Terrorism.