A former S-21 interrogator yesterday testified that he could recall just one prisoner who was not tortured under his questioning, and told the Khmer Rouge tribunal that some female detainees were raped at the notorious security centre.

Lach Mean described how interrogators were instructed to be “thorough” when extracting confessions, and that “scribbling or guesswork” would not be tolerated.

“Sometimes we have to threaten the prisoners to ensure they give us the correct answers,” Mean explained.

He said former S-21 chairman Kaing Guek Eav – better known as Duch, and convicted in the tribunal’s Case 001 – would be sent confessions and give feedback. If he deemed prisoners had not yet yielded all of their answers, interrogators would resume questioning.

For those who implicated senior Khmer Rouge cadre – including Son Sen and current defendant Nuon Chea – Mean said Duch would sometimes tell him to “skip” those names, as victims might be attempting to attack the regime or were simply speaking out of fear.

“I sought his advice when the prisoner implicated senior officials because I felt afraid that this could have serious implications,” Mean said.

He described relentless campaigns of questioning, with the shortest interrogations lasting an entire week, and longer ones extending up to a month and prisoners questioned for 12 hours each day.

The typical physical “coercion” included beating with tree branches and sticking an electric wire to a prisoner’s earlobe.

He testified that one female detainee, sent to S-21 for committing a “moral offence” and becoming pregnant, “disembowelled herself, that is, she cut open her abdomen with a razor”.

Mean said he was never present for the interrogation of female detainees, which were conducted behind locked doors, but he typed their confessions.

He said a messenger who raped a prisoner under a staircase at the prison later disappeared, while an interrogator who drugged and raped a detainee tried to commit suicide by jumping from the top floor of the centre, but became entangled in electrical cables and was arrested.

Nuon Chea made a rare appearance in court yesterday, announcing he wished to make a statement about the Vietnamese and S-21 before the trial chamber. He is expected to make his statement today.