Suffice to say that the plan to hijack an airplane and fly it in to the CIA headquarters was made known by the terrorists as a consequence of the investigations.
This Bojinka, where they planned to blow up 5 to 10 jets plying east Asian routes (Manilla, Taipi, Japan, Hong Kong, Singapore) concommitantly with assassinating the Pope in the Philippines and the stuff they learned from the first WTC bombing and the African embassy bombings should have led investigators to put two and two together better than they did.
But it was the time of Clinton.
Borderless Network of Terror:Bin Laden Followers Reach Across Globe
It's a good read, some of these SOB's were American Citizens, born and raised here in the USA.
I have a sneaking suspicion that the fourth September 11 plane that crashed in Pennsylvania was heading for Langley, per the original conception -- all this talk of it heading to the White House or the Capitol being propaganda to cover the grotesque nature of the intelligence/enforcement failure.