While many prisoners of Tuol Sleng were simply tortured and executed under the Khmer Rouge, the administrator of the prison told tribunal judges Tuesday he had conducted experiments on some of them.

“First, live prisoners were used for surgical study and training; second, blood drawing was also done,” said Duch, who is undergoing the UN-backed court’s first atrocity crimes trial.

Duch said he forced some prisoners to eat medicine tablets.

“I did it myself,” he said.

Prosecutors charge that Duch, 66, whose real name is Kaing Kek Iev, oversaw the deaths of 12,380 people while he was head of Tuol Sleng and the nearby “killing fields” of Choeung Ek, on the outskirts of the city.

Duch has denied killings by his own hand and has sought to portray himself as a loyal revolutionary caught up in a killing machine.

Tuol Sleng, known to the Khmer Rouge as S-21, was the main torture center for the regime, and became the depository for assumed traitors and spies.

Duch said Tuesday the medical experimentation was another type of crime committed under his purview.