A former guard at the infamous S-21 prison told the Khmer Rouge tribunal yesterday how he rose through the ranks to become a typist and interrogator at the centre where thousands perished under the Democratic Kampuchea regime.

Now a rice farmer in his late fifties, Lach Mean worked as a guard at Ta Khmau prison before being transferred to the S-21 security centre, also known as Tuol Sleng.

“My role was to make sure that I was vigilant . . . make sure that the prisoner did not break their shackles or that they did not try to commit suicide by hanging,” Mean said.

He testified that prisoners felt hopeless and scared, and that there were “bleeding scars and wounds on the backs, hands and feet of the prisoners”.

“Prisoners who were transported out never returned. They fully disappeared,” he said.

As a typist, he said that he recorded what he believed to be the genuine confessions of traitors, “but there were also some prisoners who gave answers without any truthful reflection”.

Mean claimed to have interrogated 10 prisoners at most and was tasked with extracting confessions to expose CIA and KGB networks.

“We received such instruction that anyone brought into S-21 was considered a traitor of the nation. That was the clear instruction from the upper echelon,” he said.

“For those prisoners who refused to confess, those prisoners would be tortured.”

Meanwhile, Tay Teng, a former S-21 guard who said he was required to dig pits and undertake executions at the Choeung Ek killing fields, finished his testimony before the court, detailing how prisoners were killed with iron bars and car axles to the loud whirring of a nearby generator.

Some time after his cousins were arrested and sent to S-21, Teng himself was sent to Prey Sar to farm rice and dig canals with those who had been accused of “immorality” until the Vietnamese forces arrived in January of 1979.

“The works at the site were for tempering the people,” he said.

However, Nuon Chea defender Victor Koppe called Teng’s account into question, citing a court record of a re-enactment that indicated Teng was “disoriented” before pointing out landmarks at the Choeung Ek site.

The witness repeatedly apologised for his scant memory, but confirmed he stood by the statements he made to investigating judges eight years ago.

“A piece of wood fell on my head, and as a result, my memory since that time has not been good,” Teng said.

Testimony is set to continue today.