The Khmer Rouge tribunal has summoned two scholars to discuss particulars of the massacres at Tuol Sleng prison, with the trial of the head of the facility, Duch, set to continue later this month.

The court has called Craig Etcheson, an author and founder of the Documentation Center of Cambodia; and Nayan Chanda, a former reporter for the Far Eastern Economic Review, to testify on Tuol Sleng, known to the Khmer Rouge as S-21.

Duch’s trial, which began in earnest March 30, will continue May 18.

Etcheson will explain the implementation of the Khmer Rouge S-21 policy, and Nayan Chanda will explain further functions of the prison when the trial resumes, according to a tribunal statement.

“They are very important for the court,” tribunal spokesman Reach Sambath said.

Youk Chhang, director of the Documentation Center, said the two were necessary to provide an analysis of the workings of the prison, which prosecutors say oversaw the torture of more than 12,000 Cambodians, who were later executed at mass grave sites outside Phnom Penh.

Duch, 66, whose real name is Kaing Kek Iev, is facing a number of atrocity crimes for his role as chief of the prison, and the experts will be needed to help understand the role of the prison within the regime.