Ieng Sary, the former Khmer Rouge foreign minister who died Thursday at the age of 87, was a student radical who emerged as one of the few public faces of Cambodia's brutal 1970s regime.
After a long battle with health issues including heart problems, he died before Cambodia's UN-backed court could deliver a verdict on his role in a regime blamed for up to two million deaths.
Ieng Sary had been on trial alongside two other senior Khmer Rouge leaders since late 2011, but he shed little light on his part in the horrors by exercising his right to remain silent.
The oldest and most frail of the trio, he spent his last weeks not in the courtroom but in hospital with a number of serious ailments.
Like his co-accused, he denied charges of war crimes, genocide and crimes against humanity.
His wife Ieng Thirith, the regime's former social affairs minister, was supposed to be in the dock with him, but she was freed in September after being diagnosed with dementia and deemed unfit for trial.
"I would like to know the truth about a dark period in our history," Ieng Sary told investigating judges after his arrest in 2007, demanding proof of his culpability in his country's "Killing Fields" era.
After that, he stayed mostly quiet about his case.
Ieng Sary was as likely a candidate for prosecution as anyone in a shrinking and ageing pool of potential defendants.
As the Khmer Rouge's foreign minister he oversaw the return of Cambodian diplomats under the guise of rebuilding their battered country.
This policy would, however, deteriorate into the wholesale purging and slaughter of intellectuals, many of them taken from his foreign ministry with his knowledge, according to observers.
"Ieng Sary appears to have contributed to the perpetuation of atrocities in (Cambodia) by encouraging the party's execution policies," said genocide researchers Stephen Heder and Brian Tittemore in their book "Seven Candidates for Prosecution."
But as much as he was an advocate for the regime during its 1975-1979 reign of terror, Ieng Sary's defection to the government 17 years later proved a death blow to the already disintegrating movement, which by then had been driven into the jungles of Cambodia's remote northwest.
His departure came two years before the death of Khmer Rouge leader Pol Pot, whom he first met at school in the capital Phnom Penh and later joined at university in Paris as eager supporters of the communist movement there.
Ieng Sary's modest roots -- he was born to a poor ethnic Khmer family in south Vietnam in 1925 -- proved a firm foundation for his later plunge into nationalist struggle.
He married Khieu Thirith in Paris in 1951, an intellectual who was also the sister of Pol Pot's new wife Khieu Ponnary.
After returning to Phnom Penh with his bride, he quickly rose through the ranks of the Cambodian Communist Party.
Both Ieng Sary and his brother-in-law Pol Pot were targetted as subversives by authorities in 1963 and fled with their wives to the jungles of Cambodia's northeast.
In 1971, Ieng Sary was dispatched to Beijing to force support for armed struggle from an exiled Prince Norodom Sihanouk, who was being urged by China to link up with Cambodian communists following his ouster in a coup the year before.
In 1979, he fled to Thailand after Vietnamese troops and Khmer Rouge defectors swept through Cambodia. He was sentenced in absentia to death by a Vietnamese-backed war crimes tribunal hastily convened that year.
In the years of fighting that followed, Ieng Sary continued to be a crucial link between the Khmer Rouge and China, a key source of money, arms and other support.
But during the 1990s, the aid dried up and a bitter power struggle among Khmer Rouge leaders was starting to cripple the movement.
Amid moves against his ally Pol Pot and accusations from former comrades that he had plundered millions of dollars worth of timber and gems, Ieng Sary defected to the government in 1996 with thousands of Khmer Rouge fighters.
He was given an amnesty for the 1979 sentence by Sihanouk, who had been re-installed as king in 1993. Sihanouk himself died last October at the age of 89 after a tumultuous life and career.
Ieng Sary and his wife lived freely in the capital until they were both arrested at their luxurious villa in 2007.
The tribunal decided in November 2011, just weeks before the start of the trial, that Ieng Sary's 1996 amnesty did not bar him from further prosecution, despite his lawyers' objections.
"I don't think he believed he had ever done anything criminal, and I think he felt insulted - and betrayed by (Prime Minister) Hun Sen, perhaps -- by being brought to the court," said historian and Cambodia expert David Chandler.
Ieng Sary is survived by his wife, their son and three daughters.