From 1989 until 2000, Nabil al Marabh, an Al Qaeda operative, lived in Boston and worked there as a cab driver. He was a "sleeper agent." He lived and worked for several years with another terrorist named Raed Hijazi. In NOVEMBER 2000, Hijazi was arrested in connection with a failed bomb attempt in Syria and BEGAN TO COOPERATE WITH INTERROGATERS. HE IDENTIFIED AL MARABH AS AN AL QAEDA OPERATIVE. This is nearly a full year before Sept 11, 2001. The details of the story are here.

The administration knew about Nabil al Marabh as reported by Judith Miller and Tim Golden in the New York Times on Sept 18, 2001.  Note now soon after 9/11 this story appeared.

On Sept 3, 2002, Nabil al Marabh was ordered deported to Syria, the US government saying that it did not have enough information to hold him. At the time, if memory serves, lawmakers were upset that he was released. That he was released makes sense to me if in fact, as i believe, federal investigators learned the full details of the pending plot by surveilling this man. Releasing him makes him less obviously a suspect in the attacks and discourages speculation that the government might have known what he knew.

As i've noted in previous posts, inference is an imperfect tool with which to attempt to ascertain "truth."  But when one adds the clues such as John Ashcroft's ending his use of civilian airlines shortly before 9/11 and the fact the the president just happened to be in perhaps the safest state in the Union (30 miles from CENTCOM HQ), it all does fit a pattern.  And just because one promulgates a conspiracy theory doesn't necessarily mean that the conspiracy didn't occur.