Secret documents reveal that the three Qatari men conducted surveillance on the targets, provided support to the plotters and had tickets for a flight to Washington on the eve of the atrocities.
The suspected terrorists flew from London to New York on a British Airways flight three weeks before the attacks.
They allegedly carried out surveillance at the World Trade Centre, the White House and in Virginia, the US state where the Pentagon and CIA headquarters are located.
Ten days later they flew to Los Angeles, where they stationed themselves in a hotel near the airport which the FBI has now established was paid for by a convicted terrorist, who also paid for their airline tickets.
Hotel staff have told investigators they saw pilot uniforms in their room along with computer print outs detailing pilot names, flight numbers and times and packages addressed to Syria, Afghanistan, Jerusalem and Jordan.
On September 10 they were booked on an American Airlines flight from Los Angeles to Washington, but failed to board. The following day the same Boeing 757 aircraft was hijacked by five terrorists and crashed into the Pentagon.
But, instead of boarding the American flight, the Qatari suspects named as Meshal Alhajri, Fahad Abdulla and Ali Alfehaid - flew back to London on a British Airways flight before returning to Qatar. Their current location is unknown.
Investigators are also hunting a fourth man, Mohamed Al Mansoori, who they say supported the alleged terrorist cell while they were in the US.
The man, who is from the United Arab Emirates, previously lived in Long Beach, Los Angeles. His current location is also unknown, and US officials recommended that he is put on an international terror watch list because he may pose a threat to aviation in the US and abroad.
The details of the secret 9/11 team have emerged in a secret American government document obtained by the Wikileaks website and passed to The Daily Telegraph. It was sent between the American Embassy in Doha and the Department for Homeland Security in Washington.
The document, sent on 11th February 2010, states: Mr Al Mansoori is currently under investigation by the FBI for his possible involvement in the 11 September 2001 attacks. He is suspected of aiding people who entered the US before the attacks to conduct surveillance of possible targets and providing other support to the hijackers.
Details of the unknown 9/11 alleged plotters has never previously been disclosed. An official inquiry into the 9/11 attacks, which killed nearly 3,000 people, indicated that the hijackers may have received assistance in Los Angeles but investigators did not publicly provide more details.
The 9/11 Commission report, published in July 2004, states that at least two of the hijackers previously visited Los Angeles but, at the time, investigators appeared to have little information on their movements. The report states they had a "brief stay in Los Angeles about which we know little".
Only one person Zacarias Moussaoui - has been tried and convicted over involvement in the 9/11 attacks as all the terrorists died in the crashed planes. Moussaoui, accused of being the twentieth hijacker, was sentenced to life in prison.
The secret American document contains detailed information about the movements of the three alleged Qatari plotters.
They took BA flight 185 from London to New York on 15th August, 2001, and the memo alleges that they subsequently conducted surveillance on potential targets ahead of the 9/11 attacks. It states: They visited the World Trade Centre, the Statue of Liberty, the White House and various areas in Virginia.
They then flew on an American Airlines flight from Washington to Los Angeles, arriving on 24th August and checking into a single room at a hotel near the airport. They paid for the room with cash and during the last few days of their stay requested that their room should not be cleaned.
The cable states: Hotel cleaning staff grew suspicious of the men because they noticed pilot type uniforms, several laptops and several cardboard boxes addressed to Syria, Jerusalem, Afghanistan and Jordan in the room on previous cleaning visits.
The men had a smashed cellular phone in the room and a cellular phone attached by wire to a computer. The room also contained pin feed computer paper print outs with headers listing pilot names, airlines, flight numbers, and flight times.
While in the US, they were aided by Mohamed Ali Mohamed Al Mansoori. The secret document also states that the three Qatari men spent a week travelling with Mr Al Mansoori to different destinations in California.
The Qatari men were scheduled to board American Airlines Flight 144 on September 10th from Los Angeles to Washington but did not turn up.
They instead boarded a British Airways flight to London, before flying back to Doha on another BA flight.
The following day the same American Airlines aircraft, flying on route AA77, was hijacked as it returned from Washington and crashed into the Pentagon, killing 184 people.
It is not known whether the FBI believe that the men were simply assisting the hijackers or were a fifth cell who pulled out at the final moment. Alternatively, they may have been planning an attack on the West Coast of America or even London which was abandoned or went wrong.
Mr Al Mansoori has never been publicly named in connection with the 9/11 attacks. The three Qatari men were included on an FBI list of more than 300 people who were wanted for questioning in connection with the 9/11 attacks, which was leaked in 2002.
At the time, the FBI stressed it was not a list of suspects, but merely parties they thought might have information useful to the investigation.
The US embassy cable obtained by the Daily Telegraph was written by Mirembe Nantongo, the deputy chief of mission in Doha. It was marked priority and sent to the office of Hillary Clinton, the US Secretary of State, the Department of Homeland Security, the FBI and the CIA.
Mr Al Mansooris visa was revoked after the information about him came to light, but his name was not watchlisted in the class system, suggesting he may have managed to leave America.
A spokesman for the FBI declined to comment.
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Government it is necessary to remove from the minds of men their individualism,
their loyalty to family traditions and national identification" Brock Chisholm - Director of the World Health Organization
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