CRUDE drawings have provided a shocking new insight into brutal torture the US Central Intelligence Agency inflicted on suspects in the wake of the September 11 terrorist attacks.

The images - hand-drawn by Libyan citizen Mohamed Ben Soud, who was interrogated inside a secret CIA prison for almost a year - depict the varied cruel torture techniques he was forced to endure including:

A sleep-deprivation technique. Courtesy of the American Civil Liberties Union

● Being shackled to an overhead bar to deprive him of sleep.

The water board. Courtesy of the American Civil Liberties Union

● Being strapped to a water board, spun around and doused with water, while interrogators threatened to force water directly into his mouth.

A coffin-like locked box Mohamed Ben Soud was forced into. Courtesy of the American Civil Liberties Union

● Being stuffed into confinement boxes.

A windowless box Mohamed Ben Soud was made to stay in. Supplied

● Being handcuffed inside a windowless box.

A drawing of Mohamed Ben Soud cramped cell inside the CIA interrogation site. The bucket is for human waste. Supplied

● Being confined to a tiny cell containing little more than a bucket for a toilet.

The pictures have come to light as part of a potentially groundbreaking civil case in the United States that is attempting to hold accountable the two psychologists responsible for developing the CIA's brutal interrogation program.

Mr Ben Soud and two fellow detainees - Tanzanian fisherman Suleiman Abdullah Salim and Afghan citizen Gul Rahman, who died as a result of his torture - are suing doctors James Mitchell and Bruce Jessen for designing, implementing and profiting from their torture.

In a motion filed by the American Civil Liberties Union (ACLU), the men argue that the doctors "aided and abetted the torture and other cruel, inhuman and degrading treatment that they suffered in the CIA interrogation program".

"Specifically, [the] plaintiffs were subjected to systematic and prolonged abuse in CIA custody, including the repeated infliction of physical assault, sleep deprivation (accomplished by forcing plaintiffs to stand for days in diapers [nappies] with their arms chained overhead), and confinement in coffin-like boxes," the motion reads.

"The use of these specific methods on [the] plaintiffs was not happenstance; it was part of a standardised program of systematic abuse that [the] defendants designed, tested, implemented and promoted, and from which they handsomely profited."

Suleiman Abdullah Salim is one of the plaintiffs in the case. American Civil Liberties Union

ACLU lawyer Steven Watt said the lawsuit was significant because all other cases on the issue had been dismissed and this was the first time CIA officials have had to justify the controversial program under oath.

"You often hear 'landmark' being bandied about, but this is a landmark case," Mr Watt told news.com.au.

DOCTORS' LIST OF 'ENHANCED INTERROGATION TECHNIQUES'

After the attack on New York's World Trade Center in 2001, the US was desperate to stop the next deadly terrorist attack on its home soil.

In 2002, the CIA recruited Drs Mitchell and Jessen to come up with a new interrogation program that could squeeze information out of captives.

A scathing Senate report into the program, which was declassified in 2014, noted that "neither psychologist had any experience as an interrogator, nor did either have specialised knowledge of al-Qaeda, a background in counter-terrorism, or any relevant cultural or linguistic expertise".

On the CIA's orders, the doctors created a notorious list of 10 "enhanced interrogation techniques", which included:

● The "walling technique", which saw detainees slammed against a wall.

● "Cramped confinement", where detainees are placed in a dark box for up to 18 hours.

● "Insects", where bugs are placed in the box with the detainee.

● "Stress positions", such as sitting on the floor with legs extended straight and armed raised above the head for hours on end.

● "Sleep deprivation" for up to 11 hours.

● The "water board technique", where the detainee is strapped upside down to a board while the water is poured onto a cloth placed over his mouth and nose. The method restricts the detainee's airflow and simulates drowning and suffocation.

The psychologists personally used these techniques on some of the CIA's most significant detainees, according to the Senate report.

Three years later, the doctors formed their own company to carry out their work with the CIA and were awarded $US81 million before the contract was cancelled in 2009.

The Senate report found that the enhanced interrogation techniques were not effective in acquiring intelligence and that they were "brutal and far worse" than the CIA made out.

INTERROGATION LEAVES LASTING SCARS

Mr Ben Soud's lawyers say he was "humiliated, degraded and suffered excruciating pain because of the abuse he endured".

Their motion to the court claims that he was kept naked or in a nappy for about two months, slammed into walls, physically assaulted through facial and abdominal slaps, hung by his wrists to deprive him of sleep, stuffed into boxes and forced to contort his body into painful stress positions for hours at time.

"While enduring prolonged standing sleep deprivation, he began to hallucinate and became hysterical," his lawyers say.

Mohamed Ben Soud. American Civil Liberties Union

While he didn't endure the waterboarding technique described in the doctors' "enhanced interrogation techniques" list, he was subjected to a variation, where water was forced into his mouth while he was strapped to a board.

He was also repeatedly doused with gallons of icy water, sometimes while wearing a hood, which had the effect of simulating drowning.

In depositions published by The New York Times, Drs Mitchell and Jessen say that if the interrogation techniques were administered correctly, they would not create lasting psychological effects on the detainee.

"The pressure is designed to be used in a way that it doesn't harm but it makes someone uncomfortable; they're more irritating than painful," Dr Jessen said.

Dr Mitchell, meanwhile, said that the "walling" technique was "discombobulating … not painful".

"It's like being on one of those whirligigs or something," he said.

He also argued that waterboarding was designed to make the detainee "uncomfortable".

"It sucks. I don't know that it's painful but it's distressing," he said.

However, Mr Ben Soud says he still stuffers from nightmares and anxiety as a result of his torture.

"It comes to me during my sleep and as if I'm still imprisoned in that horrible place and still shackled," he said in his deposition. "I get the feeling of worry about my future and about the fear that this could happen again."

He has been diagnosed with post traumatic stress disorder and had a psychotic episode as a result of the sleep deprivation techniques.

"He has been damaged psychologically and physically, without question," Mr Watt told news.com.au.

Mr Ben Soud was captured by the CIA because he was a member of the Libyan Islamic Fighting Group, which aimed to overthrow Muammar Gaddafi's regime. It was recognised as a terrorist organisation, but the group denies that it has links to al-Qaeda.

Mr Watt said his client was a "very principled individual" and "freedom fighter" who was not an enemy of the United States.

"His whole life was about freedom and liberty and democracy," Mr Watt said.

He was never charged with a crime in the US.

'WE WERE SOLDIERS DOING WHAT WE WERE INSTRUCTED TO DO'

In their depositions, given in January, Drs Jessen and Mitchell argued that they were not the "architects" of the interrogation program and that they were pressured to continue the scheme.

"I think any normal, conscionable man would have to consider carefully doing something like this," Dr Jessen said, according to the Times.

"I deliberated with great, soulful torment about this, and obviously I concluded that it could be done safely or I wouldn't have done it."

Dr Mitchell said once told the head of the CIA's Counter-terrorism Center, Jose Rodriguez, that they wanted out of the program.

"What they said was, 'You guys have lost your spine'," he said.

"I think the word that was actually used is that 'You guys are pussies'. There was going to be another attack on America and the blood of dead civilians are going to be on your hands. If you won't follow through with this then we're going to send somebody out who will."

Dr Jessen said: "They kept telling me every day a nuclear bomb was going to be exploded in the United States and that because I told them to stop I'd lost my nerve and it was going to be my fault if I didn't continue.

"We were soldiers doing what we were instructed to do."

The doctors also pointed out that, while they did use the techniques on some suspects, they did not personally interrogate the two surviving plaintiffs and had never met them.

The also argue that the interrogation techniques had been authorised by the Justice Department and that the CIA developed and controlled the program, not them.

Mr Watt promised that the eventual trial, scheduled to begin on September 5, would "shed incredible light on this very dark time in America's history".