Kaing Guek Eav - better known as Duch, who headed the S-21 prison in Phnom Penh - is charged with crimes against humanity and is the first of five defendants scheduled for long-delayed trials by the U.N.-assisted tribunal. The hearing Tuesday was procedural, and testimony was expected to begin only in late March.
Duch, driven to the hearing in a bulletproof car from a nearby detention center, intently followed the proceedings in a courtroom packed with some 500 people.
"It is not only me wanting justice today. All Cambodian people have been waiting for 30 years now," said Vann Nath, one of less than 20 survivors of S-21, who attended the hearing. "I look at Duch today and he seems like an old, very gentle man. It was much different 30 years ago."
Vann Nath, who survived by painting and sculpting portraits of Khmer Rouge leader Pol Pot, described Duch as a "very cruel man."
Duch, 66, is accused of committing or abetting a range of crimes including murder, torture and rape at S-21 prison - formerly a school - where up to 16,000 men, women and children were held and tortured, before being put to death.
"This first hearing represents the realization of significant efforts to establish a fair and independent tribunal to try those in leadership positions and those most responsible for violations of Cambodian and international law," presiding judge Nil Nonn told the chamber.
Duch has made no formal confession. However, unlike the other four defendants, Duch "admitted or acknowledged" that many of the crimes occurred at his prison, according to the indictment from court judges. Duch, who converted to Christianity, has also asked for forgiveness from his victims.
Duch has been variously described by those who knew him as "very gentle and kind" and a "monster."
"Duch necessarily decided how long a prisoner would live, since he ordered their execution based on a personal determination of whether a prisoner had fully confessed" to being an enemy of the regime, the tribunal said in an indictment in August.
In one mass execution, he gave his men a "kill them all" order to dispose of a group of prisoners. On another list of 29 prisoners, he told his henchmen to "interrogate four persons, kill the rest."
After the fall of the Khmer Rouge, Duch disappeared for two decades, living under two other names and as a converted Christian before he was located in northwestern Cambodia by a British journalist in 1999.
Taken to the scene of his alleged crimes last year, he wept and told some of his former victims, "I ask for your forgiveness. I know that you cannot forgive me, but I ask you to leave me the hope that you might."
His defense lawyer Francois Roux said Tuesday that his client has been in detention for nine years, nine months and seven days, adding, "This situation is unacceptable."
When the communist Khmer Rouge came to power in 1975 after five years of bitter civil war, many of their countrymen thought peace was at hand. But in their effort to remake society, they instituted a reign of terror that lasted nearly 4 years, until ended by an invasion by neighboring Vietnam.
Many victims feared that all the Khmer Rouge leaders would die before facing justice, and getting even one of them on trial is seen as a breakthrough. But there are concerns that the process is being politically manipulated and that thousands of killers will escape unpunished.
Duch's hearing before the tribunal was expected to last two or three days.
The trial comes 30 years after the fall of the Khmer Rouge, 13 years after the tribunal was first proposed and nearly three years after the court was inaugurated.
The tribunal has been plagued by political interference from the Cambodian government, allegations of bias and corruption, lack of funding and bickering between Cambodian and international lawyers.
Some observers believe Prime Minister Hun Sen - a former Khmer Rouge officer himself - is controlling the tribunal's scope by directing the decisions of the Cambodian prosecutors and judges.
The Cambodian side in the tribunal has recently turned down recommendations from the international co-prosecutor to try other Khmer Rouge leaders, as many as six according to some reports. This has sparked criticism from human rights groups.
"The tribunal cannot bring justice to the millions of the Khmer Rouge's victims if it tries only a handful of the most notorious individuals, while scores of former Khmer Rouge officials and commanders remain free," the New York-based Human Rights Watch said in a release Monday.
Others facing trial are Khieu Samphan, the group's former head of state; Ieng Sary, its foreign minister; his wife Ieng Thirith, who was minister for social affairs; and Nuon Chea, the movement's chief ideologue.
All four have denied committing crimes.