PHNOM PENH, Cambodia (CNN) -- The U.N.-backed genocide tribunal opened its first formal hearing in the Cambodian capital on Tuesday with the alleged chief torturer of the Khmer Rouge the first to appear.
Kaing Guek Eav is accused of carrying out executions and torture at the Tuol Sleng interrogation center.
1 of 3 Kaing Guek Eav, alias Duch, was the first of five defendants to appear before the panel for a pretrial hearing. He is charged with carrying out mass executions and torture while serving as commandant of the Tuol Sleng interrogation center in Phnom Penh.
About 17,000 political prisoners were tortured at -- and only seven survived -- the notorious prison. The victims' faces, names and details were recorded in files and photographs, including mug shots taken before and after torture.
The tribunal was created to bring to trial the surviving leaders of the Khmer Rouge on charges of crimes against humanity in connection with the Communist movement's violent reign. The tribunal includes three Cambodian and two international jurists and is expected to continue until 2010.
On Monday former Khmer Rouge Prime Minister Khieu Samphan was arrested and formally charged, the fifth ex-Khmer Rouge official arrested by the Extraordinary Chambers of the Courts of Cambodia since September.
Khieu will face an initial hearing before the tribunal either Wednesday or Thursday, said Yves Sorokobi, a spokesman for U.N. Secretary-General Ban Ki-moon.
Last week the U.N. tribunal arrested Ieng Sary, the regime's former foreign minister, and his wife, Ieng Thirith, who was also Khmer Rouge member. Ieng Sary was charged with war crimes and crimes against humanity, and his wife faces charges of crimes against humanity, the ECCC said.
The top surviving Khmer Rouge leader, Nuon Chea, was arrested in September and faces trial before the special tribunal on charges of war crimes and crimes against humanity.
In all, more than 2 million people died during the party's efforts to transform Cambodia into an agrarian utopia before troops from neighboring Vietnam overthrew the regime.
Remnants of the Khmer Rouge continued to battle Cambodia's government into the 1990s before fragmenting in the middle of the decade.
In an interview with CNN, Chom Mai recalled his time incarcerated by the Khmer Rouge.
"It was very painful, because through all of it I never knew what I had done wrong," he said through a translator. "What mistake could I have made that they could hit me and torture me? I still don't know." Watch a survivor revisit his prison and his memories »
Khmer Rouge leader Pol Pot, known as "Brother Number One" during the group's four years in power, died in a jungle hideout in 1998.
And Ta Mok, the former Khmer Rouge military chief known as "The Butcher," died in a Cambodian military hospital in 2006 while awaiting trial for crimes against humanity.