Forget for one moment everything you've been told about September 11, 2001. Instead let's ask ourselves one question: What was 9/11? A terrorist atrocity? An attack on America? The first salvo in a new war? "A day that changed everything"?

The question may seem simple, but how we answer it is of vital importance. It determines how we proceed with our investigation of that day. And once you strip away the emotional rhetoric and the fear-inducing imagery, we're left with a simple truth: 9/11 was a crime. And as with any crime, there is one overriding imperative that detectives must follow to identify the perpetrators: follow the money.