Jamie Gorelick.
Ding Ding! Ding!!
We have a winner!
The Gorelick memo stovepiped agency information which, if shared, would have indicated something brewing well enough in advance to thwart the plot.
It is entirely likely this was done to keep other actions of the Clinton Administration, conducted for fun and profit, from being discovered by agencies which had not been thoroughly contaminated with corrupt officials.
As a legacy which the Bush Administration failed to identify and resolve, the information being sent to the top without any interagency communications and feedback made the entire plot possible.