French citizen Zacarias Moussaoui, dubbed the "20th hijacker," made the revelations in court papers filed in a New York federal court by lawyers for victims of the attacks who accuse Saudi Arabia of supporting Al-Qaeda.
The Saudi embassy denied the allegations, branding Moussaoui "a deranged criminal whose own lawyers presented evidence that he was mentally incompetent."
At trial in 2006, his lawyers argued that he suffered from paranoid schizophrenia and he exhibited stormy and unpredictable behavior in court.
In testimony he said he created a database of Al-Qaeda donors, including members of the royal family, such as former intelligence chief Prince Turki al Faisal and Prince Bandar bin Sultan, who was Saudi ambassador to the United States for 22 years until 2005.
Moussaoui said he met in Afghanistan an official from the Saudi embassy in Washington to discuss Al-Qaeda's plots to attack the United States, and that he was supposed to meet the same man again in the US capital for help on a plot to shoot down Air Force One.
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He also claimed there were direct dealings between senior Saudi officials and then Al-Qaeda chief Osama bin Laden, saying he traveled to Saudi Arabia twice to deliver handwritten letters between the Al-Qaeda mastermind and senior Saudis, including Prince Turki.
Denying the claims, the Saudi embassy said in a statement: "The September 11 attack has been the most intensely investigated crime in history and the findings show no involvement by the Saudi government or Saudi officials."
Moussaoui, who was found criminally responsible at his trial in 2006, pled guilty to plotting the deadliest terror attacks in US history and is incarcerated at a supermax prison in Colorado.
A defense psychologist testified at Moussaoui's trial to say he exhibited classic symptoms of schizophrenia.
Across 127 pages of transcript, Moussaoui said the money from wealthy Saudi donors was "crucial" to Al-Qaeda in the late 1990s.
He talked about donations of two to three million dollars and said top-ranking officials were close to bin Laden -- a fellow Saudi -- through social connections.