The notorious commander who oversaw the mass murder of at least 14,000 Cambodians died on Wednesday at the age of 77.
Known as "Comrade Duch," Kaing Guek Eav was former Prime Minister Pol Pot's premier executioner and security chief at the notorious Tuol Sleng prison.
A tribunal spokesman for the Khmer Rouge, which Duch was a leader of, said he died at the Khmer Soviet Friendship Hospital in the Cambodian capital, Phnom Penh.
He gave no details of the cause, but Duch had been ill in recent years.
In the streets of Phnom Penh on Wednesday, locals like 66-year-old Cheak Sam Oeun reacted to the news:
"I will never forget the horrible past or crimes that he committed and he deserves to serve more prison terms but now that he has died, I can forgive him and his case is finished."
Duch was the first member of the Khmer Rouge leadership to face trial for his role in a regime responsible for at least 1.7 million deaths in the "killing fields" of Cambodia --during the Khmer Rouge's reign of terror from 1975 to 1979.
In 2010, a United Nations 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.
By the time of his trial, Duch was a born-again Christian and expressed regret for his crimes.
Under his 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.
At S-21, new prisoners had their mugshots taken.
Hundreds are now on display within the crumbling walls of the prison, which has since been converted into a museum.