By Jonathan Marcus
BBC Diplomatic Correspondent
The National Commission on Terrorist Attacks Upon the United States - to give its full title - has a wide brief.
No links have yet been found between Iraq and al-Qaeda
It does not just look at what went wrong with America's defences on 9/11, but also suggests remedial action for the future.
The commission is due to complete its work by the end of July.
But over the past few months it has published some preliminary statements setting out what it has found on a range of issues, from aviation security to the relationship between law enforcement and intelligence organisations.
It is all building up into a complex picture of missed opportunities - and some of it does not make pleasant reading for the Bush Administration.
This latest publication is entitled 'Overview of the Enemy' and it looks at the development of al-Qaeda, its history and evolution.
It also looks at the links that al-Qaeda fostered with some governments, notably the Taleban regime in Afghanistan.
But it is the commission's blunt statement that it has found no credible evidence that Iraq and al-Qaeda cooperated in attacks against the United States that has attracted most attention.
Iraq's alleged links with al-Qaeda were part of the justification that the Bush administration gave for launching its invasion to topple Saddam Hussein's regime.
So far no convincing evidence has been found to substantiate such a link.
Indeed, most administration spokesmen have quietly backed away from the allegation.
All, that is, except Vice-President Dick Cheney who continues to stress the link between Iraq and, as he puts it, the terrorist threat to the United States.
Now an independent commission has weakened that case even further.