A detainee at a CIA "black site" was left with permanent brain damage after agents used him as a living doll to teach trainee interrogators how to torture, declassified documents have revealed.
Ammar Al-Baluchi - a Pakistani 9/11 suspect still being held at Guantanamo Bay - was routinely and repeatedly tortured by CIA agents while at a secret facility north of Kabul, Afghanistan known as "Cobalt".
Details of the methods used on Baluchi - which date back to 2008 - were revealed in documents declassified on Thursday.
The report shows that the CIA went well beyond their usual techniques in Baluchi's case, and would strip him naked with trainees queuing up to smash his head into a wall. .
Officers at the site - known as the "Salt Pit" and dubbed "the darkness" by prisoners - tested torture methods without approval from chiefs at the intelligence agency, the documents show.
Baluchi remains in custody at the CIA's infamous Guantanamo Bay site and is one of five set to face a military court for his alleged involvement in financing the 9/11 terrorism plot.
The case itself has been on hold for over 10 years because lawyers have argued the testimony gathered under torture should not be allowed in court.
The report is largely redacted, but there are several passages detailing the type of abuse he was subjected to.
Officers at Cobalt, where prisoners were so broken they are said to have voluntarily put themselves on the water-boarding rack, used Baluchi as a living doll to demonstrate unapproved torture techniques to other agents.
The report details how officers used a technique known as "Wailing" to terrorise Baluchi.
He would be naked when interrogators-in-training would line up to repeatedly slam his head into a wall made of plywood while he was restrained with a towel.
The report explains: “The interrogators would grab the ends of the towel in front of and below the detainee’s face and shove [Mr Baluchi] backwards into the wall, never letting go of the towel."
Baluchi has spoken before about his ordeal, with it only now being officially confirmed in the CIA's declassified papers.
The horrors were made public as part of a legal challenge for Baluchi to be checked over by an independent physician.
CAGE, an NGO campaigning for "rule of law and end to the injustices of the War on Terror" published an interview with the suspect on their website.
In it, Baluchi said: “After US government agents shaved my head, they smashed my head against the wall repeatedly. It continued until I lost count at each session.
“As my head was being hit each time I would see sparks of lights in my eyes. As the intensity of the sparks were increasing as a result of repeated hitting. All of a sudden I felt a strong jolt of electricity in my head then I couldn’t see anything and everything went dark and I passed out.”
“The US government had both my hands tied together by tight handcuffs for about 120 days straight,” he added. “They had to cut the handcuffs by bolt cutters because the handcuffs got so rusted that wouldn’t open with keys.”
Baluchi was 25 in 2003 when he was taken from Karachi in Pakistan and into US custody in what his lawyers claim was an "extra-judicial" arrest.
The black site where the torture took place has reportedly been destroyed.
