Faith and Doubt at Ground Zero.

For many Americans, the most difficult questions about 9/11 were not about politics, military strategy or homeland security. They were questions about God, about evil and about the potential for darkness within religion itself. What was it we saw on Sept. 11? Was it the true face of evil? Was it the face of religion? And where, if one is a believer, was God on that tragic morning? A PBS Frontline special.