Chief Khmer Rouge interrogator Duch stood before the U.N.-backed Killing Fields tribunal on Tuesday, the first public appearance by a senior Pol Pot cadre at the court investigating Cambodia's genocide.

The grey-haired ex-commandant of the S-21 interrogation centre, now 66, sat impassively in the dock as prosecutors read out allegations of torture during a televised bail hearing.

Many people were brutally tortured and killed. They were killed with electric shocks, their finger nails were pulled off and they were beaten, co-prosecutor Chea Leang told the court.

Those acts at S-21 were done under the orders of the suspect, she said, arguing that Duch might try to flee the country if he were released on bail.

Duch, also known as Kaing Guek Eav, is appealing against his detention last July when he was charged with crimes against humanity by the joint court set up to prosecute those most responsible for the 1975-79 Khmer Rouge reign of terror, one of the darkest chapters of the 20th century.

His appearance at the specially built court on the outskirts of Phnom Penh was a significant step for the tribunal, officials said, after a decade of delays caused by wrangling over jurisdiction and cash.

Today is a milestone event in the history of the extraordinary chamber, said Peter Foster, spokesman for the Extraordinary Chambers in the Courts of Cambodia, as the tribunal probing the 1.7 million deaths of the Khmer Rouge era is called.

Dressed in a white shirt and holding his palms together in a sign of respect, Duch told the five Cambodian and foreign judges his detention violated Cambodian law.

I launched the appeal because I have been detained without trial for 8 years, six months and 10 days, said Duch, who before his July arrest was held in military prison since 1999.

THOUSANDS TORTURED

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.

(Writing by Darren Schuettler; editing by Rosalind Russell and Roger Crabb)