Former S-21 chief Kaing Guek Eav told the Khmer Rouge tribunal yesterday that if he had known the true threat Vietnamese troops posed to the regime in 1979, he would have destroyed the deadly prison.

Eav, better known as Duch, said he was instructed by Case 002 defendant and Khmer Rouge head of state Khieu Samphan to continue working as usual, and not to destroy the slew of photographs and documents produced at the prison where more than 12,000 were sent to their deaths.

“If I knew about that, then I would have destroyed the prison. That is the fact,” Duch said. On the eleventh – and what was expected to be the final – day of testimony from Duch, tensions ran high.

Victor Koppe, defence laywer for former “Brother Number 2” Nuon Chea, waded through delays and confusion as he confronted the witness with documents in which 10 Khmer Rouge combatants claimed there was a planned coup to overthrow Pol Pot.

The scheming for an uprising is a core part of Chea’s defence, which claims the threat of a Vietnamese-backed rebellion from within fuelled the ensuing internal purges. But Duch dampened Koppe’s evidence, saying he had never heard of alleged rebel plans to storm Pochentong Airport or Radio Phnom Penh.

“I believe this statement is rather imaginative; it is surreal,” Duch said. As the day’s final session began, Koppe began his questioning with: “Mr Witness, let’s see if you can sabotage this one as well.” Koppe withdrew the remark after objections from the prosecution, but proceeded to spar with the bench, accusing trial chamber president Nil Nonn of assisting the sabotage. “It’s a travesty here,” Koppe said.

Duch also took a shot at defence lawyer for Khieu Samphan Anta Guisse, who repeatedly pressed him for clarity on his long and sometimes convoluted answers. “I believe that is clear enough [for] someone who has a brain to think,” Duch said.

He said that while “S-21 was the anti-spy unit, and the [Vietnamese were] considered spies and we had to purge all those reactionary elements”, there was no document or policy explicitly outlining a targeted attack on Vietnamese people, former Lon Nol soldiers, or Cham Muslims – three groups the accused are charged with systematically killing.

“No, there was no policy to exterminate Cham people, and if a Cham committed a mistake, he or she would be arrested,” Duch said.

Prosecutor Dale Lysak, however, pointed out a former statement in which Duch admitted that, though he saw no document to that effect, Lon Nol soldiers were nevertheless “systematically eliminated”.