Duch, 67, whose full name is Kaing Guek Eav, ran the Tuol Sleng prison, where "enemies" of the regime were sent.

He has admitted overseeing the deaths of up to 15,000 people who passed through its gates and asked for forgiveness during the public hearings.

He was the first of five surviving senior figures of the Khmer Rouge to go on trial, is widely expected to be found guilty of war crimes and crimes against humanity when the court in Phnom Penh delivers its verdict.

Despite acknowledged his role he played at Tuol Sleng, codenamed "S-21", he insisted that he had only been following orders from his superiors, and on the trial's final day in November shocked many by asking to be acquitted.

"I tried to survive on a daily basis, and that's what happened. And yes, you can say I am a cowardly person," Duch had earlier testified.

But prosecutors said the former maths teacher ordered the use of brutal torture methods to extract "confessions" from detainees - including pulling out toenails and administering electric shocks - and approved all the executions.

A meticulous record-keeper, Duch built up a huge archive of photos, confessions and other evidence documenting the those held at Tuol Sleng.

In one memo he kept, a guard asked him what to do with six boys and three girls accused of being traitors. He replied: "Kill every last one."

Prosecutors have asked for a 40-year prison sentence from the judges.

Up to two million people died because of the policies of the Khmer Rouge, which ruled Cambodia from 1975-1979.

They included the evacuation of cities, forced labour in the rice fields and the summary execution of those considered enemies of the revolution.

The group's top leader, "Brother Number One" Pol Pot, died in 1998.