The Khmer Rouge tribunal has summoned as a witness Tuol Sleng photographer Nhem En, to appear before investigating judges.

Nhem En said Tuesday he had received a summons earlier this month, requesting him at the courts Nov. 1. He will be the highest-profile witness so far to undergo questioning by tribunal judges.

"I got the letter of invitation of Oct. 17, and they asked me to go on Nov. 1," Nhem En said. "I will go to see the court and testify, without fear" of being prosecuted.

His summons is likely for the case against Kaing Khek Iev, alias Duch, the former director of Tuol Sleng, where up to 16,000 Cambodians were executed and dumped into mass graves outside the capital.

Held by military courts since 1999, Duch was turned over to the tribunal in July. A hearing to decide whether he will be released ahead of trial will be held Nov. 15, tribunal spokesman Reach Sambath said.