JOURNALISTS are trained to mourn, and Marines are trained to fight. With that in mind, you can see the problem facing Brian Steidle, a retired captain in the USMC and the subject and narrator of the documentary The Devil Came on Horseback. Steidle was a military observer with the African Union for six months just as the Darfur situation worsened. With camera and notebook, Steidle recorded the aftermath of the attacks and suffered all the resulting nightmares. As an unarmed observer, his problem was obvious. Some of the most eloquent parts of The Devil Came on Horseback consists of Steidle's accounts of his frustration at watching a convoy of murderers—and not having a gun in his hands.

The dreaded janjaweed—mounted thugs with guns, "devils on horseback"—have been spending the last few years crushing a popular uprising in the south of Sudan. These rapists, castrators, child burners and systematic annihilators of villages have really only been opposed by the African Union, a group even more powerless than the U.N. Because black slavery was still going on in Sudan up to 2001, the janjaweed attacks are as much racist as they are political. There have also been efficient; the janjaweed have killed an estimated 400,000 and sent 2.5 million refugees into exile.

Sudan's government supports the raiders with air cover, weapons and money, covering for the janjaweed with what could be called implausible deniability. Confronted with evidence, Sudan's dictator Omar al-Bashir told the U.N. Assembly, "We are the government, and we will do the right thing."

It is not blaming America first to consider that the United States might be persuaded to do something about Darfur. China, which is importing 80 percent of Sudan's oil, isn't going to do anything to disturb that flow. The Arab countries, reportedly so sensitive to the mistreatment of Muslims everywhere, are standing by mute as the janjaweed murder their co-religionists. (Bin Laden, being bin Laden, has broadcast his support for the forces destroying Darfur.)

There's blame to go around, but there are also opportunities. And we have a chance to intervene in an actual genocide instead of weeping about it later. As I was saying, journalists are trained to mourn. But as we see in The Devil Came on Horseback, Steidle keeps fighting. He took his photos to the U.S. government, which is still dawdling over any potential action. (They're the government, and they will do the right thing.)

Now, Steidle is on the lecture circuit, trying to keep Darfur in the public eye despite both Sudan's craven denial and public apathy. On the recording track of one of his videos, Steidle says, "If these pictures reach the American public, there will be troops in here in a matter of days." It's been a matter of years now, but it's still not too late. Savedarfur.org.

The Devil Came on Horseback (Unrated; 85 min.), a documentary by Ricki Stern and Anne Sundberg, opens Aug. 24 at selected theaters.

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