All you need to do is watch the interview.

She actually tells you how many people would need to be involved to ignore a report on the attack. It's not that many. They knew that the plan was to attack the towers, they didn't arrange it so many other people did. They just purposely ignored the intelligence.

It also gives them plausible deniability right from the get-go that the attack wasn't their plan. Allowing it to happen by planning their defenses to be open isn't hard. The defense secretary hands down an order to drill on this day - and it's done.

Yhorian