They tried to stop the killing. Nobody listened. Now, the truth will be told. A French priest in Cambodia. An idealistic U.S. Senate staffer in Iraq. A Canadian general in Rwanda. Each one tried to focus the world's attention on genocide. Each time, they were shunned, ignored or told it was someone else's problem. CNN's Christiane Amanpour traveled to the world's killing fields to understand the world's indifference, even as courageous voices tried to "Scream Bloody Murder." A CNN worldwide investigation and two-hour documentary.