Phnom Penh - Lawyers for the former chief torturer of Cambodia's genocidal Khmer Rouge on Wednesday requested his release from prison, one day after he made a historic public apology and admitted guilt before a UN-backed tribunal.

Kaing Guek Eav, known by his revolutionary alias Duch, faces charges of crimes against humanity, torture, premeditated murder and breaches of the Geneva Conventions, but defence lawyers said his almost 10 years of pre-trial detention violated international law and the Cambodian constitution.

"Based on the facts, on Cambodian law and international precedents, there is no legal basis for the pre-trial detention," Duch's French Lawyer Francois Roux said. "His detention should have only lasted three years."

Roux said his client should be released for the duration of his trial, which began on Monday and is expected to run until mid-July, and transferred to a "safe house."

In the first trial before the tribunal, the 66-year-old former mathematics teacher faces a maximum sentence of life in prison for crimes he allegedly committed as head of the notorious Tuol Sleng torture prison in Phnom Penh during the ultra-Maoist regime's 1975-79 reign.

Duch on Tuesday begged his victims, their families, and the country for forgiveness, declaring he was responsible for thousands of deaths for which he felt "heartfelt sorrow."

"May I be permitted to apologize to the survivors of the regime and the families of the victims who had loved ones who died brutally," he said. "I ask them to please open a window and let me ask for forgiveness."

It was the first time any Khmer Rouge leader or apparatchik had made such an apology.

Duch is one of five former Khmer Rouge leaders facing trial for the deaths of up to 2 million people from execution, starvation or overwork as the fanatical regime sought to transform Cambodian society into a socialist utopia and erase history.

Cambodian co-prosecutor Chea Leang argued that Duch should not be released from detention because his personal safety would be at risk and social order would be jeopardized.

Duch sat impassively through Wednesday morning's session, occasionally taking notes and gazing into the 500-seat public gallery.

Toch Mom, a 50-year-old Buddhist monk who came to watch the trial said he believed Duch's apology was genuine.

"I believe he is telling the truth when he says he's sorry," he said. "I lost six family members because of the Khmer Rouge, so I am here to see justice in action."

Earlier this week the court was told that prisoners were routinely tortured, shackled in tiny cells for almost 24 hours a day, were not permitted to speak unless being interrogated, received barely any food and were "forced to urinate in jerry cans and defecate in ammunition boxes."

More than 12,000 men, women and children were tortured at the prison, and most were sent to be murdered at the Cheong Ek "Killing Fields." (dpa)