The war crimes tribunal hearing criminal cases against leaders of Cambodia's Khmer Rouge regime says the group's chief executioner — already serving a life sentence for crimes against humanity — will testify against his superiors.

Judge Nil Non, in a statement , said Kaing Kek Iev, better known as Duch , will testify when the trial resumes next month against three of the most senior surviving leaders of the Khmer Rouge. The ultra-Maoist regime ruled Cambodia from 1975 to 1979, and is blamed for the deaths of some 1.7 million people by overwork, starvation, torture or execution.

Authorities say Duch provided much of the evidence against nominal Khmer Rouge head of state Khieu Samphan, reputed chief ideologue Nuon Chea and Khmer Rouge government minister Ieng Sary, who are currently facing an array of charges linked to their rule.

“Many of the documents the prosecutor used to lay charges against the accused in case number 2 are based on Duch's confession. His testimony is very crucial.”

Duch was sentenced to life in prison earlier this month for overseeing the notorious Khmer Rouge Tuol Sleng torture prison, where as many as 14,000 Cambodians died. In handing down the sentence, the tribunal called the prison “a factory of death,” and described Duch as “a shocking and heinous character” who deserved “the highest penalty available.”