Him Huy, a former guard at Tuol Sleng prison, told judges at a UN-backed tribunal Monday Duch had ordered large-scale killing between 1977 and 1978 as administrator of the Khmer Rouge prison.

Duch, whose real name is Kaing Kek Iev, is facing atrocity crimes charges at the tribunal, including torture and murder, for his role as chief of Tuol Sleng, known to the Khmer Rouge as S-21, where prosecutors say 12,380 people were tortured and sent to their deaths.

“When we went to join the training course held by Duch, Duch said that he ordered us to kill all—not only the prisoners at S-21, but all prisoners in Cambodia,” Him Huy told the court.

All prisoners should be taken away from the prison to be killed at Choeung Ek, on the outskirts of Phnom Penh, Him Huy said, and Duch provided a list of names of those to be executed.

More than 100 women and children were killed among the prisoners at Choeung Ek, he said.

Duch denied the accusations Monday, telling the court he was not involved in ordering the mass killing.

Today, the Choeung Ek “killing field” is a tourist site, commemorated with a stupa filled with the skulls of victims exhumed from the area’s mass graves after the ouster of the communist regime.