The extent of Nuon Chea’s knowledge of, and executive responsibility for, the regime’s strict ideological control was the focus of yesterday’s hearing with the prosecution continuing to present documentary evidence to bolster their case.

Key evidence came from interviews between Nuon Chea and journalist Thet Sambath, as chronicled in his 2009 film Enemies of the People and book Behind the Killing Fields.

In an excerpt read from the book, Chea said that regime “enemies” had to be killed because of a lack of prisons.

“If we kept them they would spread and produce their eggs and many more would have been killed,” he said.

Chea maintained he was “not sad or scared” when his close friends were killed because “friendship and political work were separate” and the killing was always “deserved”.

Prosecutor Dale Lysak sought to paint Chea as the “key ideologue of the regime” who was responsible for significant Khmer Rouge policies.

Lysak presented diplomatic documents indicating that Chea, generally regarded as Pol Pot’s right hand man, served as acting Democratic Kampuchea prime minister for much of 1976 to 1977.

A number of S-21 confessions bearing Chea’s signature were also presented in order to show his authority and awareness of regime purges.

He was also said to have admitted to Sambath that at some point in the late 1970s he assumed control of S-21 entirely.

Chea was clear in candid interviews with Sambath that he “did not intend to be as forthcoming with this court”, Lysak said, quoting Chea as saying he would try to pin the blame on other leaders.

“We have seen this at various points from Nuon Chea,” Lysak told the court.

Perhaps thinking the film, which was not originally handed to the tribunal, would never be used as evidence, Chea showed little remorse over the policies used.

“I don’t want to be accused of being brutal but we have to consider whether it was reasonable given the threat [they posed],” he told Sambath.

“Think how threatened our country would have been had they stayed alive . . . Cambodia would have been lost for centuries . . . so I dare suggest that our decision was the correct one.”