The Khmer Rouge tribunal will increase the number of witnesses in proceedings against Duch to 13, plus 22 from civil parties, the UN-backed court announced Wednesday.

Those witnesses will include David Chandler, an expert on the Khmer Rouge and author of “Voices from S-21,” and others, who will testify between July 13 and Aug. 26, officials said.

The tribunal’s Web site said the witnesses will provide testimony on armed conflict and the functioning of Tuol Sleng, known to the Khmer Rouge as S-21, as well as Prey Sar prison, or S-24, and the Cheoung Ek execution site.

Kaing Kek Iev, better known as Duch, is facing atrocity crimes charges for his role in administering the three facilities. His case has so far seen seven witnesses, though Duch denied the testimony of one man who earlier this week said he had been released from Tuol Sleng.

Youk Chhang, director of the Documentation Center of Cambodia, said justice did not depend on the number of witnesses, but “on the quality of them.”