Tuol Sleng, the notorious Khmer Rouge prison that tortured thousands of Cambodians into fatal confessions, was inspired by a French counter-espionage service, its chief administratior, Duch, said Monday.

The structure was French, but the philosophy was Marxist, he said, adding that he had brought the idea to his superior, Son Sen, the minister of the interior and chief of the Khmer Rouge’s security apparatus.

“I said to my boss Son Sen that in France there was an intelligence agency called Service de Documentation Exterieur et de Contre Espionage [an external documentation and counter-intelligence agency], and then he advised me to set up S-21 in the way the counter-intelligence agency was run,” Duch said.

The voices of Vietnamese soldiers were recorded for radio broadcast and their photographs taken to prove to the Angkar that not a single enemy spy could escape the prison alive, Duch said.

Duch is facing charges of war crimes, crimes against humanity, torture and murder for his role as head of Tuol Sleng and other prison and execution facilities.

Prosecutors say at least 12,380 men, women and children were killed at S-21 from 1975 to 1979.

The Vietnamese are believed to have outnumbered other foreign prisoners, after armed conflict officially broke out between the communist parties of Vietnam and at the end of 1977.