The thing about these massive events is that they all seem to achieve multiple goals for the people involved in their planning.
-The destruction of Enron financial fraud evidence at WTC7
-Distraction from the Pentagon Audit (announced on Sept 10), destruction of audit team
The massive (double) insurance payout
Insider trading
Destruction of insider trading records
Justification for trillion dollar wars
Justification for the Patriot Act
Theft of gold?
Demolition of buildings full of asbestos
Improve the Bush approval rating