Ieng Sary, who co-founded Cambodia's brutal Khmer Rouge movement in 1970s, was its public face abroad and decades later became one of its few leaders to be put on trial for the deaths of an estimated 1.7 million people, has died aged 87.
His death, however, came before any verdict was reached in his case, dashing hopes among survivors and court prosecutors that he would ever be punished for his alleged war crimes stemming from the darkest chapter in the country's history.
Ieng Sary was being tried by a joint Cambodian-international tribunal along with two other former Khmer Rouge leaders, both in their 80s, and there are fears that they, too, could also die before justice is served.
Ieng Sary's wife, former Social Affairs Minister Ieng Thirith, had also been charged but was ruled unfit to stand trial last year because she suffered from a degenerative mental illness, probably Alzheimer's disease.
Lars Olsen, a spokesman for the tribunal, confirmed Ieng Sary's death. The cause was not immediately known, but he had suffered from high blood pressure and heart problems and had been admitted to a Phnom Penh hospital March 4 with weakness and severe fatigue.
"We are disappointed that we could not complete the proceeding against Ieng Sary," Olsen said, adding the case against his colleagues Nuon Chea, the Khmer Rouge's chief ideologist, and Khieu Samphan, an ex-head of state, will continue and will not be affected.
Ieng Sary founded the Khmer Rouge with leader Pol Pot, his brother-in-law. The communist regime, which ruled Cambodia from 1975 to 1979, claimed it was building a pure socialist society by evicting people from cities to work in labour camps in the countryside.
Its radical policies led to the deaths of an estimated 1.7 million people from starvation, disease, overwork and execution.
Ieng Sary was foreign minister in the regime, and as its top diplomat became a much more recognisable figure internationally than his secretive colleagues.
In 1996, years after the overthrown Khmer Rouge retreated to the jungle, he became the first member of its inner circle to defect, bringing thousands of foot soldiers with him and hastening the movement's final disintegration.
The move secured him a limited amnesty, temporary credibility as a peacemaker and years of comfortable living in Cambodia, but that vanished as the U.N.-backed tribunal built its case against him.
The Khmer Rogue came to power through a civil war that toppled a U.S.-backed regime. Ieng Sary then helped persuade hundreds of Cambodian intellectuals to return home from overseas, often to their deaths.
The returnees were arrested and put in "re-education camps," and most were later executed, said Youk Chhang, director of the Documentation Centre of Cambodia, an independent group gathering evidence of the Khmer Rouge crimes for the tribunal.
As a member of the Khmer Rouge's central and standing committee, Ieng Sary "repeatedly and publicly encouraged, and also facilitated, arrests and executions within his Foreign Ministry and throughout Cambodia," Steve Heder said in his co-authored book "Seven Candidates for Prosecution: Accountability for the Crimes of the Khmer Rouge." Heder is a Cambodia scholar who later worked with the U.N.-backed tribunal.
Known by his revolutionary alias as "Comrade Van," Ieng Sary was a recipient of many internal Khmer Rouge documents detailing torture and mass execution of suspected internal enemies, according to the Documentation Centre of Cambodia.
"We are continuing to wipe out remaining (internal enemies) gradually, no matter if they are opposed to our revolution overtly or covertly," read a cable sent to Ieng Sary in 1978. It was reprinted in an issue of the centre's magazine in 2000, apparently proving he had full knowledge of bloody purges.
"It's clear that he was one of the leaders that was a recipient of information all the way down to the village level," Youk Chhang said.
Ieng Sary was arrested in 2007, and the trial against him started in late 2011. He faced charges that included crimes against humanity, war crimes and genocide.
Only one other former Khmer Rouge official has been put on trial: former prison chief Kaing Guek Eav, who was sentenced to life in prison.
Prime Minister Hun Sen has openly opposed additional indictments of former Khmer Rouge figures, some of whom have become his political allies.
Pol Pot himself died in 1998 in Cambodia's jungles while a prisoner of his own comrades.
Ieng Sary declined to participate in his trial, demanding that the tribunal consider the pardon he received from Cambodia's king when he defected in 1996. The tribunal, formally known as the Extraordinary Chambers in the Courts of Cambodia, previously ruled that the pardon does not cover its indictment against him.
He denied any hand in the atrocities. At a press conference following his defection, he said Pol Pot "was the sole and supreme architect of the party's line, strategy and tactics."
"Nuon Chea implemented all Pol Pot's decisions to torture and execute those who expressed opposite opinions and those they hated, like intellectuals," Ieng Sary claimed.
Ieng Sary was born Kim Trang on Oct. 24, 1925, in southern Vietnam. In the early 1950s, he was among many Cambodian students who received government scholarships to study in France, where he also took part in a Marxist circle.
After returning to Cambodia in 1957, he taught history at an elite high school in the capital, Phnom Penh, while engaging in clandestine communist activities.
He, Ieng Thirith, Pol Pot and Pol Pot's wife eventually formed the core of the Khmer Rouge movement. Pol Pot's wife, Khieu Ponnary, also was Ieng Thirith's sister; she died in 2003.
Pol Pot was known as "Brother No. 1", Nuon Chea as "Brother No. 2" and Ieng Sary was "Brother No. 3."
In August 1979, eight months after the overthrow of the Khmer Rouge by a Vietnam-led resistance, Ieng Sary was sentenced in absentia to death by the court of a Hanoi-installed government that was made up of former Khmer Rouge defectors like Hun Sen, the current prime minister. The show trial also condemned Pol Pot.
Since he was in charge of the Khmer Rouge guerrilla movement's finances, Ieng Sary was believed to have used his position to amass personal wealth.
On Aug. 8, 1996, a Khmer Rouge rebel radio broadcast announced a death sentence against him for embezzling millions of dollars that reportedly came from the group's logging and gem business along the border with Thailand. But the charge appeared to be politically inspired, recognition that he was becoming estranged from his comrades-in-arms.
He struck a peace deal with Hun Sen and days later led a mutiny of thousands of Khmer Rouge fighters to join the government, which was a prelude to the movement's total collapse in 1999.
As a reward, Hun Sen, who has ruled Cambodia almost unchallenged for the last two decades, secured a royal amnesty for Ieng Sary from then-King Norodom Sihanouk, who himself was a virtual prisoner and lost more than a dozen children and relatives during Khmer Rouge rule. The government also awarded Ieng Sary a diplomatic passport for travel.
Between his defection and arrest, Ieng Sary lived a comfortable life, dividing time between his opulent villa in Phnom Penh and his home in Pailin, a former Khmer Rouge stronghold in northwestern Cambodia.
He and some of his former aides in the Khmer Rouge, intellectuals who were in a second generation of the group's leadership, made a short-lived attempt at forming a legal political movement.