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.

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.