Detainees at the notorious S-21 prison were sometimes methodically drained of blood and Western captives were publicly interrogated by prison chief Duch and burned alive, a former interrogator told the Khmer Rouge tribunal yesterday.

The witness, Prak Khan, yesterday told the court how both Vietnamese soldiers and civilians were captured and detained at S-21, including a child who was dragged away from its parents by a Khmer Rouge combatant and dropped from the first floor of a prisoner registration office.

“The child subsequently died … [The combatant] signalled me to take the dead child and bury it,” Khan said. He described how medics drew copious amounts of blood from their prisoners until they were motionless, but still breathing.

After the blood had been drawn, Khan said, prisoners “were thrown to a corner of the room and they were piled up there”, before being taken in a cart to be buried.

“I was shocked upon seeing the blood being drawn from the prisoners but I did not show it,” he said. “During the regime, I knew what was right and what was wrong . . . I did not dare to speak to anyone about it.”

Khan estimated he carried out 20 interrogations, some lasting for two months, and in his very first interrogation – of Eng Meng Heag, known as Chhon – he resorted to violence.

Khan initially refused to answer why he had beaten his prisoner, because of the “burden” the question placed on him, but relented and said he needed to “scare” the prisoner.

“I beat the prisoner with tree branches because he changed his confession … I had to use violence so that he could produce a more complete confession.”

He said S-21 head Duch – also known as Kaing Guek Eav, who was convicted in the tribunal’s Case 001 – personally interrogated American and Australian prisoners.

Although he did not witness their fate, Khan heard from fellow cadres the Westerners were taken out to the road, had tyres placed on them, and were burned.

During his testimony, Khan also detailed political study sessions, led by Duch, who instructed interrogators to humiliate prisoners and treat them like animals by making them eat faeces and worship images of dogs.

The witness also defended the killing of former Lon Nol soldiers in the days after the liberation of Phnom Penh in April 1975. “If we had not killed those people, they would have killed us back,” Khan said.