Chum Mey, who survived a notorious Khmer Rouge prison, confronted his jailer Tuesday, exchanging sharp words in a tribunal courtroom over the regime’s use of the “CIA” excuse to arrest people and describing severe, prolonged torture during his incarceration.

Chum Mey was one of the few people to live through Tuol Sleng, a prison where confessions were exacted under torture and where prosecutors say 12,380 people were sent to their deaths. Scholars say as many as 16,000 were killed there.

The former administrator, Kaing Kek Iev, better known as Duch, joined Chum Mey in court. Duch is facing a battery of atrocity crimes charges for his role as prison chief.

Chum Mey mocked the Khmer Rouge’s use of the “CIA” in its arrests during its nearly four-year rule, as cadre became increasingly paranoid their ranks had been infiltrated. Many of the accused found themselves in Tuol Sleng, suffering water-boarding, electric shock and other torture methods to have confessions forced from them.

“As an alleged CIA agent, I want to ask you, Duch, if there are any more CIA agents now?” Chum Mey asked in court Tuesday. “Already 16,000 [killed], so I just want to ask whether there are now no more CIA agents, or still a million more?”

In response, Duch addressed his former prisoner as “Brother,” saying, “the term CIA was used to arrest those against the Organization.”

“They were not really CIA agents employed and appointed by the US,” he said. “The CIA established by the communist party of Kampuchea was just to arrest people like you who were against it.”

Chum Mey is the second former prisoner to testify before the court, following the painter Vann Nath’s testimony Monday.

Now 79, Chum Mey said he was tortured for 12 consecutive days and nights after being sent to the prison in late 1978. Three of Duch’s interrogators beat him with sticks, pulled out his toenails and electrocuted him, he told the court.

His life was spared because he could repair sewing machines for the Angkar, or Organization.

“This experience of suffering has caused me such uncontained anger,” Chum Mey said. “I tell you frankly, Mr. Duch: You are lucky you did not fight me during that time. If you had, you would not now see the sunlight.”