Even Khmer Rouge security forces were killed at the regime’s notorious prison, Tuol Sleng’s director told tribunal judges Monday, underscoring how dangerous the revolutionary regime could be, even for its own adherents.

Duch, who faces atrocity crimes charges for his role as chief of the prison, said around 200 soldiers from Division 703 were killed under his supervision. Division 703, which operated in the southwest of the country, had secret agents in Phnom Penh before the regime came to power.

Soldiers from the unit were used as security personnel in Tuol Sleng. As such, they were under the supervision of Duch, and, he said, they could be killed if they were not reliable, if they were “too decisive” in their interrogations, or not decisive enough.

“For example, they were not to beat prisoners to death, but they did,” he said. “And we’d lose the confession.” Duch said even the families of the soldiers were “cleaned,” or killed.

Duch, whose real name is Kaing Kek Iev, is charged with war crimes, crimes against humanity, torture and murder for his role at Tuol Sleng, known to the Khmer Rouge as S-21.

His trial has also helped bring to light operations of the secretive regime, and on Monday, Duch described other prisons, such as S-22, a former psychological hospital in Takmao district, Kandal province; S-23, a detention center in the middle of an orchard; and S-24, Prey Sar prison.

At S-23, at least half of the patients with mental illness were killed by the Khmer Rouge, Duch said.

Prosecutors say at least 12,000 Cambodians were sent to their deaths from Tuol Sleng, which Duch ran along with Prey Sar prison and the Choeung Ek “killing field” site outside the capital.