Cambodia's UN-backed genocide court is to deliver its final verdict in the case of Khmer Rouge jailer Duch.
Duch, born Kaing Guek Eav, was sentenced to 30 years' jail in 2010 for his role in running a notorious prison where up to 15,000 inmates were killed.
The first senior Khmer Rouge official to face charges before the court, he appealed against his conviction for crimes against humanity in March 2011.
The verdict will be shown live across the country.
Hundreds of survivors are expected to turn up at the Phnom Penh court to witness the conclusion of the first case to be brought against perpetrators of crimes committed during Khmer Rouge rule.
The regime attempted to create an ideal communist society by forcing city residents to work as peasants in the countryside, and by purging intellectuals, middle class people and any supposed enemies of the state.
Up to two million people - about one-third of the population - are believed to have been killed or died of over-work or starvation.
The court's decision may have a significant impact on the tribunal as a whole, says the BBC's Guy De Launey in Cambodia.
In November 2011 the three most senior surviving leaders of the regime were put on trial for genocide and crimes against humanity.
Duch, 69, had argued that he should never have been tried, claiming that he was a junior official following his superiors' orders on pain of death. His sentence was met with disappointment from both prosecution and defence.
Many survivors were outraged because he could be free in 18 years, given time already served, if the sentence is upheld today. They are hoping for a harsher sentence.
If the court decides that Duch was indeed just a small fish, says our correspondent, then investigations into other Khmer Rouge members of a similar rank would be untenable.
Most observers do not expect Duch to go free.