A United Nations-backed tribunal in Cambodia on Thursday convicted two former leaders of the Khmer Rouge for crimes against humanity.

Khieu Samphan and Nuon Chea, sentenced to life imprisonment, were the first senior Khmer Rouge officials to face prison for their roles in leader Pol Pot’s regime, which killed nearly 2 million people between 1975 and 1979 through forced labor, evacuations, executions and starvation.