A born-again Christian, Duch has confessed in interviews with Western reporters that he committed multiple atrocities as head of the infamous Tuol Sleng, or S-21, interrogation centre.
At least 14,000 people deemed to be opponents of Pol Pot's "Year Zero" revolution passed through Tuol Sleng's barbed-wire gates. Fewer than 10 are thought to have lived to tell the tale.
Most victims were tortured and forced to confess to a variety of crimes -- mainly being CIA spies -- before being bludgeoned to death in a field on the outskirts of the city. Women, children and even babies were among those butchered.
The bail hearing serves as a dry run for the $56 million court which is due to begin full trials next year, although prosecutors say they need more time and cash.
Some 200 journalists are covering the hearing due to resume on Wednesday and televised to a potential audience of millions in Cambodia and 10 other countries.
Outside the court, hundreds of ordinary Cambodians gathered to catch a glimpse of the infamous inquisitor.
"I came here to see with my eyes and listen to Duch about what he did during the Khmer Rouge. I want to hear his confession," said 38-year-old Ali Osman.
Duch is expected to be a key witness in the trial of four other top Khmer Rouge officials, including ex-president Khieu Samphan, 78, who was accused of crimes against humanity and war crimes on Monday.
Former foreign minister Ieng Sary and his wife -- both life-long friends of "Brother Number One" Pol Pot who died in 1998 -- and "Brother Number Two" Nuon Chea, face similar charges.
The four others have denied knowledge of any atrocities as Pol Pot pursued his dream of creating an agrarian peasant utopia.
The hearing today is a major step in a long process. We are not at the end yet, we are at the beginning," said Theary Seng, a social activist whose parents died during the Khmer Rouge era.
