US intelligence officials are releasing a trail of evidence, linking Osama bin Laden to the US terror attacks.
The FBI evidence links the hijackers to bin Laden's network, through phone intercepts, money transfers and training camps.
Key evidence includes money transfers between hijacker Mohamed Atta and a Middle Eastern man named Mustafa Ahmed.
The FBI believes the transfers provide a clear link to bin Laden.
A month before the atrocities, the CIA also received information, suggesting bin Laden was determined to strike on US soil.