TUOL SLENG, Cambodia (CNN) -- The trial of a former prison chief with the Khmer Rouge movement resumed inside a packed Cambodian courtroom Monday, with prosecutors painting a grim picture of inmates who were electrocuted, whipped and beaten to death.
Duch ran a prison where people were tortured and killed under the Khmer Rouge.
Kaing Guek Eav, a former math teacher and a born-again Christian, displayed no emotion as the U.N.-backed tribunal accused him not just of overseeing the torture and killing of more than 15,000 men, women and children three decades ago -- but of actively taking part in some of them.
The trial of the 66-year-old man, better known as Duch, resumed Monday just outside the Cambodian capital, Phnom Penh.
Spectators, many of them survivors of the abuse, watched the proceedings from an auditorium separated from the courtroom by a large glass window.
The proceedings began with Duch offering a basic introduction of himself. Court officials then read out the findings of their lengthy investigation.
Prosecutors contend Duch ran S-21, a prison that had been converted from a school. Here, men, women and children were shackled to iron beds and tortured -- before they were beaten to death, prosecutors said.
Many of the victims were military officials or Communist Party members targeted for not going along with the philosophy of the ultra-Maoist Khmer Rouge movement, prosecutors said.
Duch faces charges that include crimes against humanity, war crimes, torture and murder.
The movement swept to power in 1975. Three years, eight months and 20 days later, at least 1.7 million people -- nearly one-quarter of Cambodia's population -- were dead from execution, disease, starvation and overwork, according to the Documentation Center of Cambodia.
The non-profit organization has been at the forefront of recording the atrocities committed during the Khmer Rouge regime.
S-21 was one of 189 similar institutions across Cambodia. Duch is the first former Khmer Rouge leader to stand trial.
The tribunal, which is made up of Cambodian and international judges, does not have the power to impose the death penalty. If convicted, Duch faces from five years to life in prison.
The trial is expected to last three or four months.
"Probably the most important thing about this court is: even after 35 years, you are still not going to get away with it. That is the message," said Chief Prosecutor Robert Petit.
Even though Duch was not a senior leader with the movement, many Cambodians were relieved that one of the regime's former leaders was facing justice, said Youk Chhang, head of the Documentation Center of Cambodia.
"I think there is a feeling of, well you know, finally -- now it's finally happening after all these years of waiting -- hearing, fighting, negotiating," he told CNN last month. "People have that kind of sense of relief that it's now moving. When I ask people around the center today, people say, 'Oh, it's about time.'"
Four of the regime's former leaders, also accused of war crimes and crimes against humanity, await trial before the tribunal. The regime's leader, Pol Pot, died in 1998.
"It all seems so fresh," said Norng Champhal, who was a starving little boy when Vietnamese forces invaded the prison. He was separated from his mother after a night in the prison and never saw her again.
"It's hard to control my feelings when I see this," he said, as he watched footage of the prison taken 30 years ago. "I wonder whether my parents were tortured like these people," he said.
CNN's Dan Rivers contributed to this report.