Ieng Sary, the Khmer Rouge co-founder who was on trial for genocide and war crimes, died on Thursday, the UN-backed court said, robbing Cambodians of a verdict for his role in the murderous regime.
The death of the 87-year-old, who as Khmer Rouge foreign minister was one of the regime's few public faces, intensified fears the remaining two elderly defendants may also fail to live to see justice at the much-delayed tribunal.
"Ieng Sary died this morning after being hospitalised since March 4," court spokesman Lars Olsen said, adding it was "regrettable we cannot finish the proceedings in the case".
Charges against Nuon Chea and Khieu Samphan will not, however, be affected by Ieng Sary's death, he added.
Only a handful of top regime figures have ever come to trial over the Khmer Rouge's crimes that saw a quarter of Cambodia's population wiped out between 1975 and 1979.
The one-time radical student was the oldest of three former leaders on trial, and -- along with "Brother Number Two" Nuon Chea, 86, and former head of state Khieu Samphan, 81 -- denied charges including war crimes, genocide and crimes against humanity.
Ieng Sary's wife Ieng Thirith, the regime's former social affairs minister, was last year deemed unfit for trial after being diagnosed with Alzheimer's disease.
Rights groups expressed dismay that the ex-foreign minister cheated justice despite evidence he oversaw the wholesale purging and murder of intellectuals, many of them taken from his ministry with his knowledge.
"His death is no victory and it carries little value for the regime's victims who patiently wait to see justice done. The court must move on," said Youk Chhang, of the Documentation Centre of Cambodia, which researches atrocities by the hardline communist regime.
Ou Virak of the Cambodian Center for Human Rights, said his death was "a wake-up call... that these cases need to be expedited urgently so that justice can be served."
The court's progress has been blighted by delays with the defendants frequently unfit to attend hearings.
Funding shortages have also left the court's Cambodian workers without wages for several months and a strike over the unpaid salaries by some local staff has stretched into a second week, paralysing proceedings.
Heather Ryan, a trial monitor at the Open Society Justice Initiative, described Ieng Sary's death as "an example of 'justice delayed is justice denied'", which would "leave Cambodians with a sense of frustration".
Born to a poor ethnic Khmer family in south Vietnam, the former foreign minister repeatedly denied knowledge of the mass executions that came to define the Khmer Rouge regime, and claimed he had no powers of arrest.
While he was an advocate for the regime during its reign of terror, Ieng Sary's defection to the government in 1996 proved a hammer blow to a movement which 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 remained defiant after his 2007 arrest at a luxury villa where he lived with his wife in Phnom Penh, challenging the court to prove his guilt for the "Killing Fields" era, where huge numbers of people were slaughtered and buried in mass graves.
Led by "Brother Number One" Pol Pot the Khmer Rouge killed an estimated two million Cambodians through starvation, overwork or execution in a bid to create an agrarian utopia.
The court has so far settled just one case, sentencing former prison chief Kaing Guek Eav, better known as Duch, to life in jail for overseeing the deaths of some 15,000 people.