PHNOM PENH , Cambodia ( CNN ) -- Youk Chhang knows the truth about the Cambodian genocide perhaps better than anyone in the world . Youk Chhang runs the Documentation Center of Cambodia , which has documented 20,000 mass graves . He was 13 when the Khmer Rouge came to power . Separated from his family , forced into slave labor , beaten nearly to death for stealing rice for his pregnant sister , he saw the horrors firsthand . His mother lost a daughter and four siblings ; 30 years later she still searches for them , hoping they survived . Chhang survived by eating whatever he could find . After the fall of the Khmer Rouge , it took him months to walk home to his family . Eventually , he fled to safety in the United States . `` Food was ... more important than God , '' Chhang said . `` I always wish to have a bowl of rice . And one good night 's sleep . That 's all I wanted . I would do anything for it . '' Watch Youk Chhang talk about what he ate , how he survived » . But the ghosts of the genocide brought Chhang back to Cambodia . And for more than a decade , he has run the Documentation Center of Cambodia . `` DC-Cam , '' as it is known , is the world 's largest repository of information about the Cambodian genocide . It holds hundreds of thousands of documents , photos and films as well as interviews with both survivors and former Khmer Rouge members . Chhang said he believes the Khmer Rouge kept such careful records as a measure of their success -- a trophy of sorts . `` At each time when they kill a person , they document it so that they can measure their success one step forward , '' Chhang said . `` If they kill two , then two step forward . If they kill five , then five step forward . So to them , it 's a golden file . But I mean , to us it 's crime against humanity . '' DC-Cam has located and mapped nearly 200 prisons and 20,000 mass graves across the country . For Chhang and DC-Cam , the work is critical to preserving memory and promoting justice . Watch as Chhang takes CNN 's Christiane Amanpour into DC-Cam 's secured vault » . Today in Cambodia , a tribunal is under way to try five of the surviving leaders of the Khmer Rouge -- 30 years after their alleged crimes . DC-Cam is providing much of the evidence for use in the trial , evidence that makes plain the facts of the genocide , the scope of the losses and the personal and national grief . Chhang said he hopes the tribunal will help Cambodians move forward -- and help heal the nation he loves . But even now , the way forward is difficult . Chhang has dedicated a lifetime of work , research , preservation and advocacy to his mother , whose bravery and sacrifice inspired him . Even though his mother survived and they shared much of the same pain and many of the same losses , the two do not talk about what happened . Some in Cambodia are anxious to forget and forgive . Others are angry and searching for justice . Many , like Chhang , said that only by knowing , exploring and exposing the truth will Cambodia be able to rectify its past -- and secure a healthy future .
Youk Chhang was imprisoned when the Khmer Rouge came to power in Cambodia . He survived by eating whatever he could find and eventually escaped to the U.S. Back in his hometown , he now runs the Documentation Center of Cambodia . ` ` DC - Cam '' is the world 's largest repository of information about the country .