A former teacher was told to “cut off the wounded flesh” for the sake of the revolution after his Vietnamese wife and their three children were killed under the Democratic Kampuchea regime, the Khmer Rouge tribunal heard yesterday.

The traumatic account, related by civil party Uch Sunlay, continued the tribunal’s examination of Case 002/02’s third trial topic – the alleged genocide of Cham Muslims and ethnic Vietnamese.

In September 1978, Sunlay said, he and other workers who had Vietnamese spouses were taken on a two-day trip to cut bamboo, while his wife and children were carted away to be slaughtered. His children, he said, were “swung against a tree and died instantly”.

When the workers returned, Sunlay said his co-operative chief told them to steel their emotions before telling them their families had been taken away. “I want all of you comrades to get rid of this wounded flesh . . . in order to build the revolutionary labour class,” Sunlay recalled the co-operative chief saying. “I said what he instructed us to say, but in my heart I suffered.”

Sunlay also recounted how his father, a devout Buddhist, was killed for burning incense, while his father-in-law was forced to remarry in a ceremony of 11 couples. “All this suffering and harm cannot be forgotten,” Sunlay said.

His testimony before the court will continue today. It came after the civil party testimony of Khouy Muoy, a woman of Vietnamese and Chinese descent, who said she was “fortunate” to have survived the regime after losing her parents and siblings – 10 members of her family in total. “There is nothing that could compare to the loss of my family members,” Mouy said.

In an announcement yesterday, the court said it will begin hearing evidence on security centres and internal purges today – the fourth trial topic in Case 002/02 against former Khmer Rouge leaders Nuon Chea and Khieu Samphan.

The hearings will pinpoint alleged atrocities at Au Kanseng Security Centre, in Ratanakkiri province; Phnom Kraol, in Mondulkiri province; and Phnom Penh’s notorious S-21 prison, before moving on to allegations of forced marriage and the conflict between Cambodia and Vietnam.

According to the announcement, the court will then shift focus to the roles of Chea and Samphan in the alleged crimes, with evidentiary hearings expected to wrap up later this year and a judgement to be handed down in 2017.