(CNN) -- Bou Meng walks into a big open room, sits down on the floor and points to a number, which is stenciled on the wall. Number 13. It was his prison number and the spot on the floor where he says he was shackled in Cambodia's infamous Tuol Sleng Prison. The prisoners who entered were often killed. Bou was one of the few who survived the torture, starvation and executions routine when the Khmer Rouge were in power. Led by the late Pol Pot, the regime was responsible for the deaths of millions of ordinary Cambodians during a four-year reign of terror that was eventually halted in 1979 by invading Vietnamese forces.
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Survivors of torture, disease, starvation have many questions
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Tens of thousands died under Khmer Rouge
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Remaining leaders of Khmer Rouge to stand trial
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Thousands expected to come watch the trial
But the memories of this dark chapter continue to haunt victims such as Bou more than 30 years later, as four surviving members of the Khmer leadership, including @placeholder's "number two," prepare to stand trial for their alleged role in the genocide.