I'm quite surprised that no one has yet mentioned what I am about to discuss. Or if someone has (which is entirely possible) I haven't seen it.
The sort of intelligence failure which now seems to have occurred prior to September 11th is seldom the fault of a single individual or even a group of individuals. The problem is most often structural and organizational, a failure to devise a framework that gets the right information into the right hands in a timely fashion.
Having said that, consider this.
The key window of time for all the warnings and hints was last summer, roughly June, July and August of 2001, the period right before the attacks. No one has considered that this was also the period of time when the post of FBI Director was vacant.
Certainly something worth considering, no?
Let's review the history. On May 1st of last year then-Director Louis Freeh announced his resignation and that he would leave sometime in early June (Freeh's questionable tenure at the Bureau is another major point of concern, but that's for another post.) I'm not sure when Freeh's official last day was, but on June 22nd Attorney General John Ashcroft made Deputy Director Tom Pickard Acting Director, effective the following day.
Through May and June the White House searched for a replacement for Freeh, first focusing on Robert S. Mueller, then deciding the President wanted other choices, then finally settling on Mueller.
None of this was dilatory or out of the ordinary. But during this key period the FBI's leadership was at best in deep flux and at worst the Bureau was leaderless.