This is the moving, and horrifying, story of Brian Steidle, a captain who left the US Marines to become a military observer in Darfur in the Sudan. He took photographs of what he found there, got them published in the New York Times and spent several years trying to prompt the international community into action against what was obviously genocide.

He talked to Condoleezza Rice, who thanked him for his efforts and gave the photos back, and to Barack Obama, who told him the nation was too fixed on the problems in Iraq and Afghanistan to do much about the wholesale massacre of the people of Darfur by the Arab-run government of the Sudan.

The devils on horseback are the Janjaweed who, with the obvious if now denied complicity of the government, are still burning, raping and murdering to this day.

What Steidle did manage to secure was millions of dollars of aid from individual Americans who learned of Darfur for the first time. But, as one black Muslim, who lost both his house and half his family, tells him, there had not been a single piece of aid from any Islamic organisation, at least at the time of making the film.

This is often not pleasant to look at, but there is little doubt that the admirable Steidle’s work, put together by Annie Sundberg and Ricki Stern with a commentary from himself, ought to be shown as widely as possible on TV as well as in the cinema. Its only fault is that it doesn’t discuss the geopolitical reasons for the world’s inaction, especially after its failure in Rwanda.