The unidentified person has detailed to a US court visits to the detention facility where he witnessed inmates chained in a foetal position on the floor, with no food or water.

The court judgment said the witness was someone “apparently affiliated with the Federal Bureau of Investigation but whose identity has been redacted”.

In a document dated August 2004 and referred to in an overnight US federal court ruling, the witness says most times detainees had urinated or defecated on themselves, and had been left there for 18 to 24 hours or more.

The witness said “On one occasion, the air conditioning had been turned down so far and the temperature was so cold in the room that the barefooted detainee was shaking with cold.”

“On another occasion, the air conditioning had been turned off, making the temperature in the unventilated room probably well over 100 degrees (Fahrenheit). “

“The detainee was almost unconscious on the floor, with a pile of hair next to him.”

“He had apparently been literally pulling his own hair out throughout the night.”

“On another occasion, not only was the temperature unbearably hot, but extremely loud rap music was being played in the room, and had been since the day before, with the detainee chained hand and foot in the foetal position on the tile floor,” he said.

The Australian government has consistently maintained it has no evidence to support the abuse claims.

But David Hicks’ US military appointed lawyer, Major Michael Mori, said the evidence of the FBI witness could not be disputed.

“We know there’s abuse going on at Guantanamo and I think this is the first release of concrete evidence,” Maj Mori told AAP.

“When the government in Australia starts saying these are allegations that are being looked into – well, they’re not allegations (anymore), they’re fact … unless you think FBI agents are making it up.”

“There are abuses going on and here we have an FBI agent confirming it,” he said.