Traditionally, our best excuse for inaction in the face of genocide was that we didn’t fully know what was going on — until too late.

During the Holocaust, reports trickled out of Nazi areas of atrocities and extermination camps, but they encountered widespread skepticism. “I don’t believe you,” Felix Frankfurter, the Supreme Court justice, told Jan Karski, a Polish Catholic who at extraordinary risk had visited a Nazi death camp as well as the Warsaw Ghetto and finally escaped with hundreds of documents.

Likewise, the Turks mostly barred access to the scene as they industriously killed off Armenians (a pattern of denial that persists in Turkey today). Cambodia sealed itself off during Pol Pot’s rule. And when Westerners evacuated from Rwanda in 1994 (the French airlifted out their embassy dog, while leaving behind local employees to be butchered), few witnesses were left to chronicle the savagery day by day.

That’s what makes Darfur so unusual in the history of genocide: the savagery is unfolding in plain view, and yet as world leaders gather in Russia for the Group of 8 summit meeting, the basic international response is to look the other way.

No genocide has ever been publicly chronicled so extensively as this one. We have satellite images of the burned villages, and detailed reports from groups like Human Rights Watch and Amnesty International. Aid workers interact daily with the two million displaced people, and we can watch as Sudan spreads instability into neighboring countries.

Indeed, now we have a witness who has come all the way to America: Hashim Adam Mersal, a young man now living in Pennsylvania with the help of the Pittsburgh Refugee Center.

Mr. Hashim, who is 26, is a member of the Zaghawa tribe, which has been particularly targeted for death in Darfur. He grew up in a village called Tomorna and lived a relatively prosperous life because of his family’s large herd of 400 cattle and 150 sheep.

Then in August 2003, the Sudanese government sent the janjaweed militias to attack black African villages in his region. Mr. Hashim escaped with some of the livestock, but his father and brother (a 24-year-old father of two) were both killed, along with many others — including eight children in one family. Mr. Hashim isn’t sure what happened to the rest of his family.

“It was humans and livestock all mixed together, running for survival,” Mr. Hashim remembers. “Some kids were falling behind, and we just couldn’t help. We couldn’t do anything for those falling back. There was lots of crying, but you were too scared to stop and help anyone. Some were wounded and couldn’t keep up. Some were left behind and died.”

In that flight, Mr. Hashim passed other villages that had been burned. “Bodies were scattered everywhere,” he said.

Eventually, Mr. Hashim made his way to the Chadian capital. He used cash and tribal connections to obtain a fake Chadian passport and, somehow, a diplomatic visa to the U.S. So Mr. Hashim came to the U.S. — only to be jailed on immigration charges. He was released on bail and is fighting deportation back to Sudan; a hearing is scheduled for October.

Frankly, the best place to put Mr. Hashim isn’t in jail, but in the White House Rose Garden for a photo-op with President Bush to call attention to the genocide.

Mr. Hashim studies English into the wee hours in hopes of communicating better, so as to plead with Americans to help save his people. At the same time, he is wracked by guilt at having survived when so many others died. “I am alive and breathing, but I am like a dead man who walks,” he said. “The rest of my life will be nothing but sorrow.”

In the small community of Darfur-watchers in America, there is deepening gloom. There has been an outcry at the grass-roots level — www.savedarfur.org gathered one million signatures demanding a greater response — but the genocide is still spreading. John Prendergast of the International Crisis Group, just back from the region, warns that “the international community is actually missing the potential enormity of the crisis as it metastasizes to Chad and the Central African Republic.”

A conference of donors on Tuesday in Brussels will be an important test of whether there is any international resolve to save lives.

But increasingly it appears that even when the world has no excuse at all for inaction — when it is fully informed about a genocide in real time — it still cannot be bothered to do much about it.