Khieu Samphan and Nuon Chea are the only two senior Khmer Rouge leaders that were still alive to stand trial for their part in orchestrating the forced exodus and mass killings of millions during a period now regarded as the Cambodian Genocide.
The Khmer Rouge attempted to create an agrarian society through genocide and social engineering, forcing people out of cities and to work on rural cooperatives. The offshoot of the Cambodian Communist Party formed in 1968 and was headed by the totalitarian leader, Pol Pot.
Nearly a quarter of the population - at least two million people - died under their rule, through a combination of starvation, medical neglect, overwork and mass execution when the group held power between 1975-79.
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