(CNN) -- They share a deep sorrow: an idealistic American who tried to protect the Kurds of Iraq, a Canadian general who refused to follow orders in Rwanda, a French priest who fought for the soul of Cambodia.





CNN's Christiane Amanpour traveled to the killing fields of Europe, Africa and Asia for "Scream Bloody Murder."





Each one tried to focus the world's attention on the world's most heinous crime: genocide. Each time, they were shunned, ignored or told it was someone else's problem.





To understand why, CNN's Christiane Amanpour traveled to the killing fields of Europe, Africa and Asia for a two-hour documentary, "Scream Bloody Murder."





Having reported on mass atrocities around the world, this time Amanpour traced the personal accounts of those who tried to stop the slaughter.





The yearlong CNN investigation found that instead of using a U.N. treaty outlawing genocide as a springboard to action, political leaders have invoked reason after reason to make intervention seem unnecessary, pointless and even counter-productive.  Map: See the locations featured in the documentary »





December marks the 60th anniversary of the U.N.'s Genocide Convention, when -- in the aftermath of the Holocaust -- the nations of the world pledged to prevent and punish future attempts to eliminate ethnic, religious and national groups. Read the 1948 Genocide Convention (pdf)





"The Genocide Convention should have stopped genocide, but it didn't," said Holocaust survivor and Nobel laureate Elie Wiesel. Intervention is a daunting challenge, he believes, because of a tendency to minimize accounts from refugees and victims. "It's better not to believe, because if you believe, you don't sleep nights. And how can you eat? How can you drink a glass of wine when you know?"  See images from locations in the documentary »





1970s: Cambodia





Father François Ponchaud was a Catholic missionary in Cambodia when the Khmer Rouge guerillas -- communist revolutionaries -- seized power in 1975. They expelled all foreigners from the country.





But working from France, Ponchaud gathered refugee accounts and monitored radio broadcasts to document the slave labor, torture and executions the Khmer Rouge were using to kill one-fourth of Cambodia's population.





He published his findings in a major French newspaper and wrote a book, "Year Zero." But even so, Ponchaud tells Amanpour, "No one believed us."  Watch a behind-the-scenes look at the making of 'Scream Bloody Murder' »





1980s: Iraq





CNN found that intervention is often weighed against political and economic costs.





Declassified U.S. government documents show that while Saddam Hussein was gassing Iraqi Kurds, the U.S. opposed punishing Iraq with a trade embargo because it was cultivating Iraq as an ally against Iran and as a market for U.S. farm exports.





According to Peter Galbraith, then an idealistic Senate staffer determined to stop Hussein from committing genocide, the Reagan administration "got carried away with their own propaganda. They began to believe that Saddam Hussein could be a reliable partner." Read once-secret U.S. documents





1990s: Bosnia





Even extensive news coverage may not lead to intervention.





During the violent breakup of Yugoslavia in the 1990s, the media reported on the Bosnian Serbs' ethnic cleansing of Muslims: the siege of Sarajevo, the concentration camps, the use of rape as a weapon of war.





It was like watching "a color remake of the black-and-white scenes we'd seen in World War II," said U.S. diplomat Richard Holbrooke, whose Jewish grandfather fled Germany when Adolf Hitler came to power.





Holbrooke was an early advocate for a U.S.-led military operation against the Bosnian Serbs.





"I took a stand that I believed was correct," he told Amanpour. "I didn't think it was so controversial."





But it would take three years -- and the massacre of 8,000 Muslim men and boys in the town of Srebrenica -- for Holbrooke to make his case within the Clinton administration.





1994: Rwanda





In Rwanda, where Hutu soldiers and militias massacred their Tutsi countrymen, the Clinton administration
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