A key witness for the defence of Khmer Rouge leaders Nuon Chea and Khieu Samphan proved an unexpected stumbling block at yesterday’s hearings at the Khmer Rouge Tribunal.

Souy Sao, 60, was expected to testify to having a role in a planned coup to overthrow Pol Pot with help from Vietnam. The defence had argued that this was evidence of a legitimate threat to the Khmer Rouge leadership that provided context to the purges of cadres deemed as traitors.

Ultimately, though, the witness offered a muddied portrayal of events. In 2005, Sao had told investigators from the Documentation Centre of Cambodia (DC-Cam) that he had attended a secret meeting during the Khmer Rouge regime at which he was tasked with transporting a truck of weapons – which, he had said, was part of the coup plan concocted by Ta Oeun, the commander of Division 310.

Yet when questioned in court by the prosecution, Sao backpedalled on key details, despite insisting that his 2005 statement to DC-Cam was correct and truthful: he told the court that he had not attended a secret meeting; had never transported weapons for a coup; and had never met defendant Khieu Samphan.

However, he was able to tell the defence what had happened to Oeun. “He was arrested . . . he staged a coup at the time,” he said of his former division commander. “He wanted to topple Pol Pot’s regime.”

Nuon Chea’s defence lawyer Victor Koppe noted that a previously unnamed witness had testified that Ta Oeun was “in the same clique with [current Prime Minister] Hun Sen”.

And Koppe asked Sao what he had meant when, in his statement, he had replied to a question about the possible benefits of the trial by telling DC-Cam’s investigators: “I mean only Hun Sen’s cliques have taken all the lost property in the Pol Pot regime.”

Koppe then withdrew the question following objections that it was “outside the scope” of the trial.

Sao also told the court that although Ouen had been arrested, ordinary combatants like himself were not.

That drew a response from prosecutor Dale Lysak who pointed out that, according to prison lists from S-21 prison, Sao’s Division 310, “was one of the most heavily purged organisations” in the regime.

“Were you not aware that hundreds of your fellow combatants from Division 310 were arrested and disappeared?” Lysak asked.

Sao replied he had little knowledge of their disappearances.