Videotapes showing secret interrogations of one of the 9/11 plotters have been unearthed at the Central Intelligence Agency (CIA) in the United States.
They were found in a box under a desk at the CIA's Counterterrorism centre.
The tapes could reveal how foreign governments aided the US in holding and interrogating suspects.
They reportedly show interrogations, in a secret overseas prison, of confessed 9/11 attack plotter Ramzi Binalshibh.
The discovery of the tapes could complicate US efforts to prosecute 38-year-old Binalshibh, who has been described as one of the "key plot facilitators" in the attacks.
In New York, Bill Quigley, Legal Director at the Centre for Constitutional Rights, said the fact that the tapes had come out would "help shed light to what happened to this individual person, but will also shed light on the chain of secret prisons that the United States has maintained across the world."
The two videotapes and one audiotape are believed to be the only existing recordings made within the clandestine prison system.
The tapes depict Binalshibh's interrogation sessions in 2002 at a Moroccan-run facility the CIA used near Rabat, several current and former US officials told The Associated Press.
They spoke on the condition of anonymity because the videos remain a closely guarded secret.
Nine years after his capture, there is no indication when Binalshibh and other confessed September 11 attackers will face military or civilian trials.
While the tapes could have a bearing on any trial in the future, Binalshibh has openly admitted his role, praising the attacks.