The UN-backed Khmer Rouge tribunal is set to deliver its verdict on whether the last two surviving leaders of the Pol Pot regime are guilty of genocide.
Nuon Chea, 92, was Pol Pot’s deputy, and Khieu Samphan, 87, was the regime’s head of state.
They are on trial for genocide against Cambodia’s Cham Muslim minority and ethnic Vietnamese.
Up to two million people are thought to have died under brutal Khmer Rouge regime between 1975 and 1979.
Many of them succumbed to starvation and overwork, or were executed as enemies of the state.
The pair are already serving life sentences after they were found guilty of some crimes against humanity in 2014.
But a guilty verdict on Friday would be the first official acknowledgement that what the Khmer Rouge regime did was in fact genocide as defined under international law.
The pair will also be judged on more crimes against humanity – including murder, enslavement and torture – and violations of the Geneva Conventions.
Who were the Khmer Rouge?
The Khmer Rouge were radical Maoists who formed a regime that ruled Cambodia from 1975 to 1979, led by Saloth Sar who was better known as Pol Pot.
The regime – founded by French-educated intellectuals – sought to create a self-reliant, agrarian society: cities were emptied and their residents forced to work on rural co-operatives. Many were worked to death while others starved as the economy imploded.
During the four violent years they were in power, the Khmer Rouge also killed all those perceived to be enemies – intellectuals, minorities, former government officials – and their families.
That included people from ethnic minorities, but largely consisted of ethnic Khmer people.
The regime was defeated in a Vietnamese invasion in 1979. Pol Pot fled and remained free until 1997, and died under house arrest a year later.
Why is this tribunal controversial?
Officially called the Extraordinary Chambers in the Courts of Cambodia, this could be the tribunal’s final decision.
Established in 2006 with both Cambodian and international judges, it has so far only convicted three people for the atrocities of the Khmer Rouge regime at a cost of $300m (£231.5m).
In 2010 it convicted Kaing Guek Eav, also known as Duch, who was in charge of the infamous Tuol Sleng torture centre and prison in Phnom Penh.
Former Khmer Rouge foreign minister Ieng Sary was a co-defendant with Khieu Samphan and Nuon Chea but died before judges delivered a verdict in the first of the two sub-trials in 2014. His wife Ieng Thirith, the regime’s social affairs minister and the fourth co-defendant, was ruled mentally unfit to stand trial and died in 2015.
Although there are cases against four other Khmer Rouge members, Cambodian Prime Minister Hun Sen has been vocal about his opposition to the tribunal starting any new trials and there is little chance this will happen.
A former mid-level member of the Khmer Rouge regime himself, he says his people want to move on and that further prosecutions could lead to violence.
The Khmer Rouge waged an insurgency after they were toppled from power, although thousands defected to the government in the 1990s before the group disbanded completely in 1999. There are parts of the country where victims and perpetrators live side by side in villages.
But many Cambodians pay little attention to the tribunal, and young people in particular are keen for their country to be known for something other than the “killing fields”.