On 9/11, after the attacks had already begun, the last aircraft hijacked by al-Qaida terrorists was United Airlines Flight 93. But to this day, the ultimate target of the terrorists on this aircraft has never been confirmed.
It was on Flight 93 that the passengers learned through phone calls to loved ones that two planes had crashed into the World Trade Center. The passengers made the decision to fight back.
The 9/11 commission concluded the Flight 93 passengers may have been close to regaining control of the airplane. Cockpit recordings, translated from Arabic, indicate the hijackers became fearful of the uprising and put the aircraft into a fatal dive. In the final seconds, the hijackers can be heard saying, "put it down, put it down” and “God is great."
The airplane crashed in an empty field outside of Shanksville, Pa., just 240 miles northwest of Washington, D.C., or about another 30 minutes of flying time from the nation's capital.
Tyler Drumhiller was the head of CIA operations in Europe at the time. He suspects the target was the White House, but he is not certain, in part because intelligence intercepts suggest the al-Qaida chain of command wasn't certain either.
"I suspect the guys in Afghanistan didn't know,” Drumhiller said. “I suspect what they were doing is they were given a list of maybe 10 places -- all of the main places in Washington -- and they picked the ones they were going to go after.”
On 9/11, after the Pentagon had been hit by American Airlines Flight 77, the greatest concerns were for the CIA, the White House, and the Capitol building.
United Flight 93 left Newark, N.J., at 8:42 am ET. At 9:24 a.m., the pilot received a flight dispatch warning from air traffic controllers: "Beware any cockpit intrusion. Two aircraft have hit the world trade center."
Just four minutes later, Federal Aviation Administration flight controllers heard a commotion over the radio from Flight 93, and the aircraft dropped 700 feet. Suddenly, a voice came over the radio as the person flying the aircraft tried to talk to passengers.
"Ladies and gentlemen, here is the captain. Please sit down. Keep remaining sitting. We have a bomb on board."
The flight had been headed west and began to reverse direction, going southeast. A few minutes later, there was another transmission from the cockpit: "Uh, this is the captain. Would like you all to remain seated. There is a bomb on board and we are going back to the airport to have our demands. Please remain quiet."
Within minutes, the FAA issued a warning that an aircraft over Pennsylvania, Flight 93, had been hijacked and was now on a course towards Washington, D.C.
Just before 10 a.m., security officials in Washington, D.C., began a frantic evacuation at the U.S. Capitol building and at the White House. Police radios were filled with reports of a hijacked aircraft en route to Washington, D.C., and perhaps just minutes away.
Michael Scheuer, a former analyst at the CIA believes Osama bin Laden was very anxious to hit the White House.
"But Mohammad Atta said no," Scheuer said, "because the profile of that building is much too low. So, my own guess is that the Capitol building, the Congress, was probably the target. It stood out higher on the horizon and on the skyline, and was a better target anyway."
Scheuer agrees with the idea that even Osama bin Laden probably didn't know Flight 93's intended target.
"Bin Laden is the type of guy that is a very good delegator of authority,” he said. “It's clear from the evidence after the fact that he would have preferred to hit the White House. But on all of the targets, he deferred to the commander on the ground who was Mohammed Atta.”
Atta was on board American Airlines Flight 11 -- the aircraft that hit the World Trade Center's North Tower.
So, what was the order he gave the hijackers on United Flight 93? We may never know for sure.
But part of the reason that Flight 93's target is significant is because al-Qaida has demonstrated it doesn't give up on a building or place it wants to destroy. The World Trade Center was bombed in 1993 and it was brought down, of course, eight years later on 9/11.
The key to stopping a terrorist attack rest in part on help from U.S. allies. But did two allies who are now crucial in the war on terror -- Saudi Arabia and Pakistan -- know something ahead of time about 9/11? We will examine that question in our final report.