The bi-partisan commission established by the US Congress to investigate the attacks of 11 September 2001 has interviewed more than 1,000 witnesses, including President George W Bush, and reviewed more than two million documents over a period of 20 months.
BBC News Online charts the progress of the inquiry.
20 September 2002
President Bush gives in to political pressure and agrees to hold an independent bi-partisan investigation into intelligence failings in the months leading up to the 11 September attacks.
27 November 2002
President Bush appoints controversial veteran US diplomat Henry Kissinger to head the investigation.
Mr Kissinger resigns in December after refusing to disclose the names of his consulting firm's clients.
16 December 2002
Former Republican Governor of New Jersey Thomas Kean is appointed chair of the commission.
27 January 2004
Commission seeks an extension of its deadline to complete the investigation until July.
12 and 13 February 2004
Commission announces it is seeking public testimony from President George Bush and Vice-President Dick Cheney, former President Bill Clinton and his Vice-President, Al Gore, and senior officials, including National Security Adviser Condoleezza Rice, CIA Director George Tenet, Attorney General John Ashcroft, Defence Secretary Donald Rumsfeld and Secretary of State Colin Powell.
8 April 2004
In a public hearing, Ms Rice says there was no "silver bullet" that could have prevented the attacks on New York and Washington. She admits there could have been better intelligence sharing, but says legal barriers prevented law enforcement and intelligence agencies from pooling information.
She also reveals Mr Bush had been given a memo in August 2001 titled "Bin Laden determined to attack inside the United States".
The panel later speaks to Mr Clinton in a closed private session.
13 April 2004
Former FBI director Louis Freeh, who resigned in June 2001, tells the commission that FBI counter-terrorism operations were severely under-funded and under-staffed.
Mr Ashcroft tells the panel that years of intelligence failings made the US unable to prevent the attacks, and that his determination to fight terrorism had been hampered by the policies of the Clinton leadership.
14 April 2004
Mr Tenet tells the commission that systemic problems in the intelligence community had left the country vulnerable to attack and that the problems would take five years to fix.
He also says he did not speak to George Bush in the month before the attacks, when Mr Bush was on holiday in Texas.
In an interim report critical of the intelligence services, the commission says Mr Tenet and his deputies were presented with a briefing paper titled "Islamic Extremist Learns to Fly" in August 2001.
29 April 2004
President Bush says he and Mr Cheney have a "wide-ranging and cordial" conversation with the commission in private.
18 May 2004
The panel says the work of the emergency services in New York was hampered by poor planning, inadequate equipment, and rivalry between different agencies.
2 June 2004
Mr Tenet resigns as director of the CIA, citing "personal reasons".
16 June 2004
The commission's interim report on al-Qaeda finds no "credible evidence" that Iraq helped al-Qaeda militants carry out the terror attacks.
Mr Bush later says his administration never claimed Iraq helped co-ordinate the attacks, only that it had had contacts with al-Qaeda.
22 July 2004
Final report published.