After a four-year absence from the court that convicted him of crimes against humanity, Kaing Guek Eav, better known as Comrade Duch, returned to the Khmer Rouge tribunal to testify yesterday, calling Nuon Chea’s denial of overseeing the deadly S-21 prison “nonsense”.

Duch is the former chairman of the notorious S-21 prison, where more than 12,000 people were imprisoned, tortured and sent to their deaths. He is serving a life sentence at Kandal Provincial Prison.

The prosecution confronted the 73-year-old with a statement from current defendant and former Khmer Rouge Brother Number Two Nuon Chea, in which he denounced Duch’s last testimony in Case 002 in April 2012.

“I would like to inform the Cambodian people that I have never [at], any time – ever been responsible for the operation of S-21,” Chea had said.

“What Duch has accused me [of] has been untruthful and very unjust towards me. I have never ordered, I have never received any documents from Duch, and I have never been the superior of Duch.”

In court yesterday, however, Duch became animated, wagging his finger in the air as he decried Chea’s statement.

“I am surprised by the denial by bong Nuon; I could not believe that,” he told the court, adding that the S-21 office was under the leadership of the party, which had an official policy to “smash the enemy”.

“His denial is nonsense.”

Duch described meeting Nuon Chea for the first time on August 15, 1977, on the upper floor of a Buddhist school.

The meeting lasted all of 10 minutes, Duch said, but it was made clear Nuon Chea was his superior from then on, as his former boss, Son Sen, had been sent to the battlefield.

As his testimony continued, Duch said that from the moment he was appointed as chief of the S-21 compound, “if one was arrested, he or she was never released”.

The prosecution probed Duch on the treatment of former Lon Nol soldiers and officials – a key focus in the current phase of the trial against Chea and his co-defendant, former Khmer Rouge head of state Khieu Samphan.

Prosecutor Dale Lysak enquired about the fate of the family of Professor Thach Chea, a former advisor to the minister of education who was killed in 1974 – the year before Phnom Penh fell to the Khmer Rouge.

His four young children, Duch confirmed, were executed. “In the real situation after 17 April 1975, when the parents were taken away and killed, the children would be taken away and killed as well,” he said.

The wife of Chea – also a professor – was killed during a medical experiment carried out at S-21, where live prisoners were used for surgical training.

Duch – a deputy at S-21 at the time – said he and then-chairman Ta Nat were reprimanded for subjecting the wife of a “famous person” to such treatment.

Although he studied alongside her at the pedagogical school, Duch said he did not know how old Chea’s wife was at the time of her death. “In fact I did not even know her name,” he said.