Khmer Rouge “Brother Number Two” Nuon Chea said he would break his silence on the horrors committed during the regime, but only if an unnamed witness – believed to be National Assembly President Heng Samrin – is called to testify.

Chea, on trial for crimes against humanity, has refused to answer questions throughout the trial, despite scores of civil party witnesses tearfully pleading with him for answers.

A document from Chea’s defence, dated August 1 but made public last week, reiterated Chea would not speak unless his “only character witness”, whose name is redacted, was summonsed.

In previous court documents, Chea’s “only character witness” is listed as TCW-223; cross-referencing with other court documents identifies that code name as Samrin.

Chea’s lawyer, Victor Koppe, did not identify the witness in an email yesterday but said he was “by far the most important witness” to his case and “absolutely crucial” to a fair trial.

“He knew Nuon Chea really well. They were fellow revolutionaries for 30 years,” Koppe said, adding that the witness had previously ignored a 2009 summons and if he did not appear, “Nuon Chea will remain silent forever”.

“Now that would be tragic. For the Cambodian people and indeed also for the civil parties who ask him questions every day in court,” he said.

Government spokesman Phay Siphan declined to answer whether Samrin would appear in the event of a summons.