Comrade Duch, the executioner-in-chief for Pol Pot's genocidal ultra-communist regime which killed an estimated 1.7 million people in the 1970s, has died.
Kaing Guek Eav, better known as Comrade Duch, shown in a video grab taken during his trial in 2009. Photo: AFP
A quarter of the Cambodia's population were thought to have perished during the regime.
Comrade Duch admitted in court to being directly responsible for the death of more than 12,000 people.
Kaing Guek Eav or 'Comrade Duch' was the first member of the Khmer Rouge leadership to face trial for his role within a regime blamed for at least 1.7 million deaths in the "killing fields" of Cambodia from 1975 to 1979.
Duch died at the Khmer Soviet Friendship Hospital in Phnom Penh, Khmer Rouge tribunal spokesman Neth Pheaktra said. He gave no details of the cause, but Duch had been ill in recent years.
In 2010, a UN tribunal found him guilty of mass murder, torture and crimes against humanity at Tuol Sleng prison, the former Phnom Penh high school which still stands as a memorial to the atrocities committed inside.
He was given a life sentence two years later after his appeal that he was just a junior official following orders was rejected. Duch - by the time of his trial a born-again Christian - expressed regret for his crimes.
Under Duch's leadership, detainees at Tuol Sleng prison, codenamed "S-21", were ordered to suppress cries of agony as Khmer Rouge guards, many of whom were teenagers, sought to extract confessions for non-existent crimes through torture.
The guards were instructed to "smash to bits" traitors and counter-revolutionaries. For the Khmer Rouge, that could mean anyone from school teachers to children, to pregnant women and "intellectuals" identified as such for wearing glasses.
- Reuters and agencies