Duch subordinate details torture by electric shock, suffocation.

AFORMER interrogator at Tuol Sleng prison on Tuesday detailed an array of torture techniques used at the secret detention facility, including electric shock, suffocation and blood-drawing.

During testimony at Cambodia's UN-backed war crimes court, Prak Khan, 58, said he saw groups of prisoners being taken to get their blood drawn, adding that many of them died as a result.

"I saw detainees who were subject to blood-drawing. One detainee had roughly five bags of blood taken," he said, adding that between 10 and 20 prisoners were subjected to the process at once.

"After their blood was drawn, the prisoners would die," he said. When asked how often prisoners were taken, he said it happened "occasionally".

Prak Khan was called on to testify against his former boss, Kaing Guek Eav, alias Duch, who acknowledged earlier in his trial that blood-drawing was among the torture techniques used at the prison.

Answering questions put by Judge Jean-Marc Lavergne, Prak Khan said Duch was the one who gave lectures on how best to torture detainees.

"We were taught to insert a needle underneath the nail, and by doing so the detainee would sustain a wound on their finger [without] affecting their heart," Prak Khan said.

"It was a theory instructed to us by Duch because it was a light technique that did not affect the heart of the detainee."

He told the court that the interrogators at S-21 were forced to follow strict rules, that they were prohibited from beating detainees to death, and that they were told to be sure that no one escaped.

"We were taught how to interrogate prisoners and avoid prisoners dying, otherwise the confession would be broken and we would be punished," Prak Khan said from the dock.

"We were trained on how to whip prisoners with a stick, on how to electrocute[and] on how to use plastic bags to suffocate them."

Female prisoner tortured

Prak Khan, who was assigned to be an interrogator in 1976, said he once served as a guard outside a room in which a female prisoner under Duch's supervision was shocked and suffocated until she fell unconscious.

"They tried to interrogate that female prisoner; however, a confession was not extracted, and at 3am the female prisoner fell unconscious and was taken back to her cell," he said.

He said suicides had also been reported at the prison.

"We were told that some prisoners jumped from the building, some burned themselves with lamps, and some used a pen to prick themselves in order to die," he said.

Prak Khan said he did not want to elaborate on what kind of torture he himself used on prisoners, saying: "I will keep silent on that matter."