A twisted prison commander who orchestrated the mass murder and torture of inmates has died aged 77.
Kaing Guek Eav, or “Comrade Duch”, was a senior figure in Pol Pot’s Khmer Rouge communist regime, which ruled Cambodia from 1975 to 1979.
He ran the notorious Tuol Sleng prison, where thousands of people were incarcerated and later executed in the late 1970s.
He died at 12.52am local time (7.52pm BST) at the Khmer Soviet Friendship Hospital in Phnom Penh, Khmer Rouge tribunal spokesman Neth Pheaktra said.
A cause of death was not given, but Duch had been ill in recent years.
He 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 2010, a U.N. tribunal found him guilty of mass murder, torture and crimes against humanity at the prison, a former high school based in the capital Phnom Penh – which has since become a genocide museum.
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 his cruel leadership, guards tortured the inmates and sought to extract confessions for non-existent crimes.
They were instructed to "smash to bits" traitors and counter-revolutionaries at the prison, codenamed "S-21".
For the Khmer Rouge, that could mean anyone from school teachers to children, to pregnant women and "intellectuals" identified as such for wearing glasses.
Prisoners were initially made up of officials from the old government, people accused of being middle class and other Khmer Rouge members suspected of disloyalty.
Inmates were given electric shocks, forced to eat faeces, and covered in scorpions.
They were then put to death at the so-called “killing fields” just outside the capital.
The guards were typically aged between 15-19 and from peasant backgrounds, eager to dedicate their lives to the new regime.
Recruits had to go through months of military training and were ordered to forget about their parents and think only of the revolution.
Duch, himself a former maths teacher, had an obsessive eye for detail and kept his school-turned-jail meticulously organised.
"Nothing in the former schoolhouse took place without Duch's approval. His control was total," wrote photographer and author Nic Dunlop, who found Duch in 1999 hiding near the Thai border, two decades after the Khmer Rouge fell.
"Not until you walk through the empty corridors of Tuol Sleng does Stalin's idiom that one death is a tragedy – a million a statistic, take on a terrifying potency," Dunlop wrote in his account of Duch and his atrocities, "The Lost Executioner".
At S-21, new prisoners had their mugshots taken. Hundreds are now on display within its crumbling walls.
Norng Chan Phal, one of the few people to have survived S-21, was a boy when he and his parents were sent to Duch's prison and interrogated on suspicion of having links to the Khmer Rouge's mortal enemy, Vietnam.
His parents were tortured and killed but Chan Phal survived to give testimony at Duch's trial in 2010.
"He was cooperative, he spoke to the court frankly. He apologised to all S-21 victims and asked them to open their hearts. He apologised to me too," Chan Phal told Reuters.
"He apologised. But justice is not complete".