Says Dale Watson, the head of the FBI's counter-terrorism division, "I don't know what the legal limit is, but there were probably hundreds of people in here."
Watson was at the center of the storm that day. Now, as CBS News Correspondent Jim Stewart reports, he has a sobering assessment for the future. On a scale of one to ten, Watson rates the terrorist threat level today at eight — and climbing.
According to Watson, the threat is still very much at hand one year after the attacks.
"It has not decreased that much where we were from last year at this time."
First and foremost, he believes, U.S. forces in Saudi Arabia and elsewhere in the Middle East are a prime target.
Explains Watson: "Would that be a crown jewel, so to speak? Absolutely."
Inside the U.S, the city of Washington D.C. is unfinished business for al Qaeda.
"The United States capitol area is a target that people that really hate us as an organization and what we stand for, would be a likely target," he says.
But what is actually left of al Qaeda to press the attack? Not nearly as much as before, claims Watson, who personally believes Osama bin Laden is dead and confirmed the U.S. is examining corpses to prove it.
But does the United States actually have bin Laden's DNA to make such a confirmation?
"Osama bin Laden is a Saudi citizen and there are lots of ways to get DNA," Watson answers.
Meanwhile, al Qaeda's middle leadership may be taking over the reins, second-tier men like Khalid Shaikh Muhammed who helped plan the Sept. 11 attacks.
Inside the U.S., Watson confirmed the FBI is following and surveying far more suspected terrorists than previously reported. Watson says that at any given time, there are several hundred they are looking at.
As for the attack itself, there are many burning questions to be addressed. Who decided to turn hijacked planes into guided missiles? No one here knows.
And how exactly did the hijackers get in the cockpits? Watson's not sure, but he postulates the pilots themselves may have opened the doors for breakfast.
Says Watson, "Pilot, co-pilot, probably drinking, wanted a cup of coffee."
Or more puzzling, what was Mohamed Atta, the hijacker ringleader, doing on repeated visits to Las Vegas?
Watson himself has a barrage of questions. "What's he doing out there? Why does he fly out there first class and then stay in a lower-priced hotel? How long was he there?"
Again, there are no answers, only questions. But the thinking in the room is that Washington and New York are not alone on al Qaeda's all-American hit list.