On Sept. 11, 2001 — it all seemed so sudden, and without warning. But three years and two investigations later, it's clear there was a tragic trail of missed opportunities to stop some of the hijackers, disrupt the plot and perhaps save 3,000 lives. Here are nine of them:
The Malaysia meeting
January 2000: Top al-Qaida operatives converge on Kuala Lampur for a planning meeting that that includes two of the 9/11 hijackers — the first time a hijacker comes on the radar of American intelligence. The CIA loses track of the hijackers, and fails to watch-list them or warn the FBI one has a valid visa to enter the U.S. "It's one of those critical nodes where we could have disrupted the 9/11 plot well before it ever got off the ground," says NBC analyst and terrorism expert Roger Cressey.
The calls
Once in the U.S., one of the hijackers gets up to a dozen calls from a known al-Qaida switchboard in Yemen. The National Security Agency is listening, but doesn't figure out that the calls are to someone inside the U.S.
The walk-in
April 2000: Niaz Khan, who says he was trained by al-Qaida, walks into an FBI office with an incredible tale. "I've been to Pakistan, I know about this hijacking, something going on. … I told them before 9/11, about more than a year, be … hijacking in America or on an America airline," Khan tells federal agents. He says he was sent to the U.S. to join operatives here. Khan passes two polygraphs, but FBI headquarters doesn’t believe him and lets him go.
The sighting
In the fall of 2000, a predator spy drone captures extraordinary live pictures of al-Qaida training camps in Afghanistan — including a tall man in flowing white robes believed to be Osama bin Laden. "This was the equivalent of having bin Laden in the crosshairs," says NBC terrorism analyst Steve Emerson. But no military assets were on standby to take a shot.
The Phoenix memo
A prophetic memo in July 2001 by a Phoenix FBI agent warns bin Laden may be training pilots at American flight schools. The memo gets buried in FBI Headquarters.
The Moussaoui arrest
Suspected terrorist Zacharias Moussaoui is arrested while training at a Minnesota flight school. But the FBI wouldn’t allow agents to search his computer, which would have tied him to the plotters. "The Moussaoui episode is one of the top three examples of where we might have been able to stop 9/11," says Cressey.
The search
In late August 2001, the CIA finally tells the FBI that two hijackers may be in the country, but the FBI can’t find them — even though they're listed in the San Diego phone book.
The watch list
The two hijackers are added to the watch list, but never put on the Federal Aviation Administration’s "no fly" list, because they hadn’t previously shown interest in hijacking planes.
Air defenses
Sept. 11, 2001, 8:24 a.m. ET: A hijacker, believed to be Mohammed Atta, thinks he's talking only to passengers when he says — "We have some planes. Just stay quiet and you'll be OK. We are returning to the airport." The FAA repeatedly fails to alert the military's air defense system until it's too late. Chaos and confusion reign. When F-16s do scramble, some fly in the wrong direction and aren't even told to look for hijacked planes.
"If you look at the details of what these 19 men did on the 11th of September, they defeated every defense that we had in place, every single one of them. And there is no other word that you can put on it other than that they defeated the U.S,” says 9/11 commission member and former Democratic Sen. Bob Kerrey.
After analyzing more than 1,000 interviews and millions of documents, the 9/11 commission does not conclude 9/11 could have been prevented. Delayed? Disrupted? Probably. We'll never know.
But the commission says everyone at all levels of government should have been more ready.