In 1974, Thet Sambath’s father became one of the nearly two million people who were murdered by the Khmer Rouge when he refused to give them his buffalo. Sambath's mother was forced to marry a Khmer Rouge militiaman and died in childbirth in 1976, while his eldest brother disappeared in 1977. Sambath himself escaped Cambodia at age 10 when the Khmer Rouge fell in 1979. Fast forward to 1998, and Sambath, now a journalist, got to know the children of some senior Khmer Rouge cadre and gradually earned their trust. Then, for a decade, he spent weekends visiting the home of the most senior surviving leader, Nuon Chea, aka Brother Number Two under Pol Pot. "But he never used to say anything different from what he told Western journalists," says Sambath, "I was low-ranking, 'I knew nothing, I am not a killer.' Then one day he said to me 'Sambath, I trust you, you are the person I would like to tell my story to. Ask me what you want to know.' For the next five years he told me the truth, as he saw it, including all the details of killing." Sambath also won the confidence of lower-level Khmer Rouge soldiers, now ordinary fathers and grandfathers, who demonstrated for him how they slit people's throats. It was the first time these murderers admitted what they had done. He taped their interactions, and together with British documentarian Rob Lemkin created this landmark film.