US investigators were today analysing the black-box data recorder from the hijacked plane which crashed in a field in Pennsylvania.
The recorder, which could hold crucial evidence of the minutes before it crashed, was last night the first to be recovered from the three crash sites.
It was found in the crater caused by the impact of the plane plunging into a field in Shanksville, killing all 45 on board, CNN reported.
The hunt was still under way for the voice data recorder, which will allow investigators to hear what the hijackers said for at least 30 minutes before the crash.
The data recorder was last night on its way to Washington DC where it will be examined by experts to reconstruct the last minutes in the air.
The find came as firefighters working in the remains of the shattered wing of the Pentagon said they were hopeful of finding the black box from the plane which crashed there.
Captain Scott MacKay told CNN its signal had been picked up by searchers in the rubble and it was hoped to be able to positively locate it soon.
The FBI believe the plane which crashed in Pennsylvania was going to be used to attack Camp David, but there have been claims the White House may have been the target.
There have also been reports that the Capitol building, where Congress sits, was intended for destruction.
Passengers on the plane are believed to have agreed to try to overpower the hijackers as they had already learned of the attack on the World Trade Center.
Mr Thomas Burnett phoned his wife and told her of the hijack, asked her if the reports of the World Trade Center attacks were true, then put down the phone and returned shortly afterward.
His mother-in-law Joanne Makely told CNN: "The men voted to attack the terrorists. He left the phone and said he would be back. That's the last we heard." Mr Jeremy Glick called his wife Liz and in-laws in New York to say all 38 passengers, and possibly the crew, had been herded to the back of the plane.
Air traffic controllers heard someone shout "get out of here" through an open microphone.
The plane, which took off from Newark bound for San Francisco, was near Cleveland, flying at 35,000 feet. The microphone went off on again, scuffling was heard and then there was another shout: "Get out of here."
Then a voice said in an Arabic accent: "There is a bomb on board. This is the captain speaking. Remain in your seat. There is a bomb on board. Stay quiet. We are meeting with their demands. We are returning to the airport."
It was then the plane turned completely and began its course towards Washington DC but crashed.
PA