Two former Khmer Rouge prison officials said Tuesday that they had been summoned to testify against the surviving leaders of the regime before Cambodia's UN-backed genocide tribunal.
Nhem En, who was the chief photographer at the notorious Tuol Sleng prison, said that he received a summons last week ordering him to appear at the tribunal on November 1.
"It won't be a problem. I will go, I am not worried at all," Nhem En told AFP by telephone from the former Khmer Rouge stronghold of Anlong Veng near Thai border.
"I will tell the truth. I will tell the court in plain black and white everything that I know," said the 47-year-old, who was one of six photographers who took pictures of each of the victims tortured at the prison before being sent to their deaths.
Nhem En said the seniormost surviving Khmer Rouge leader Nuon Chea and the Tuol Sleng prison chief Duch, who are both in the tribunal's custody, should be held responsible for the killing of prisoners.
"If Duch had not informed the leadership about the prisoners, the Khmer Rouge leaders would have not known anything" and some of the inmates could have survived, Nhem En said.
"It is a long story to be told," he added.
Some 16,000 men, women and children were brutalised at Tuol Sleng, a high school that was converted into a torture centre, before being taken to the outskirts of the capital and executed.
Him Huy, 52, former security chief at the prison, told the English-language Cambodia Daily newspaper that he too had been summoned by the tribunal.
"I will answer what I can remember, but I won't bring any documents with me because I have no documents," the paper quoted Him Huy as saying.
Reach Sambath, a tribunal spokesman, said he could not confirm the identity of any of the witnesses for "security reasons."
The tribunal "has invited many witnesses to the court. The court will not reveal the names of the witnesses," he added.
In addition to Nuon Chea and Duch, the tribunal is investigating three other unnamed suspects for crimes committed during the communist regime's 1975-1979 rule.
Up to two million people died of starvation and overwork, or were executed under the Khmer Rouge, which abolished religion, schools and currency, and exiled millions to vast farms in its bid to create an agrarian utopia.
Khmer Rouge leader Pol Pot died in 1998.
A tribunal to try the regime's top leaders got under way last year after some 10 years in the making. Trials are expected in 2008.