Errol Morris's latest film opens April 25.

Is it possible for a photograph to change the world? Photographs taken by soldiers in Abu Ghraib prison changed the war in Iraq and changed America’s image of itself. Yet, a central mystery remains. Did the notorious Abu Ghraib photographs constitute evidence of systematic abuse by the American military, or were they documenting the aberrant behavior of a few “bad apples”? We set out to examine the context of these photographs. Why were they taken? What was happening outside the frame? We talked directly to the soldiers who took the photographs and who were in the photographs. Who are these people? What were they thinking?

Over two years of investigation, we amassed a million and a half words of interview transcript, thousands of pages of unredacted reports, and hundreds of photographs. The story of Abu Ghraib is still shrouded in moral ambiguity, but it is clear what happened there. The Abu Ghraib photographs serve as both an expose and a coverup. An expose, because the photographs offer us a glimpse of the horror of Abu Ghraib; and a coverup because they convinced journalists and readers they had seen everything, that there was no need to look further. In recent news reports, we have learned about the destruction of the Abu Zubaydah interrogation tapes. A coverup. It has been front page news. But the coverup at Abu Ghraib involved thousands of prisoners and hundreds of soldiers. We are still learning about the extent of it.

Many journalists have asked about “the smoking gun” of Abu Ghraib. It is the wrong question.

As Philip Gourevitch has commented, Abu Ghraib is the smoking gun. The underlying question that we still have not resolved, four years after the scandal: how could American values become so compromised that Abu Ghraib -- and the subsequent coverup -- could happen?

From the archive:

According to one who was present, Churchill suddenly blurted out: "Are we animals? Are we taking this too far?"

From earlier this month, President Bush:

Because the danger remains, we need to ensure our intelligence officials have all the tools they need to stop the terrorists.

Unfortunately, Congress recently sent me an intelligence authorization bill that would diminish these vital tools. So today, I vetoed it.