The boss of a prison where some 16,000 men, women and children were tortured and executed appeared before Cambodia's genocide tribunal Tuesday in its first trial over the Khmer Rouge reign of terror more than three decades ago. Kaing Guek Eav - better known as Duch, who headed the S-21 prison in Phnom Penh for the Khmer Rouge regime - is charged with crimes against humanity and is the first of five defendants scheduled for long-delayed trials by the U.N.-assisted court. They were among a close-knit, ultra-communist clique that turned Cambodia into a vast slave labor camp and charnel house in which 1.7 million or more died of starvation, disease and executions. "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 in a courtroom packed with some 500 people. "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. But the tribunal has drawn sharp criticism. Its snail-slow proceedings have 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. Duch has made no formal confession. However, unlike the other four defendants, he "admitted or acknowledged" in some of the 21 interviews by investigating judges 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." During the hearing, Roux and co-prosecutor Robert Petit sparred over whether to allow one of four children S-21 survivors to appear before the trial. Petit said Norng Chan Phal could provide "key testimony." Norng Chan Phal was an 8-year-old inmate of the torture center when troops from neighboring Vietnam stormed into Phnom Penh to end Khmer Rouge rule in 1979. He hid in a pile of inmate clothing as his captors evacuated to prison to elude approaching Vietnamese troops. His story surfaced only last week when previously unseen footage was shown of Vietnamese troops entering the prison. It included images of living children and many adult corpses, some decapitated. 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. 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. 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. The group's representative Sara Colm said at the trial, "It's very good to see Duch in the dock. It's been a long time coming. We only hope the tribunal can address the very serious issues." 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.