The United States government has never acknowledged any error in detaining Mr. Boumediene, though a federal judge ordered his release, for lack of evidence, in 2008. The government did not appeal, a Defense Department spokesman noted, though he declined to answer further questions about Mr. Boumediene’s case. A State Department representative declined to discuss the case as well, except to point to a Justice Department statement announcing Mr. Boumediene’s transfer to France, in 2009.

More than a decade has passed since his arrest in Bosnia, since American operatives shackled his feet and hands, dropped a black bag over his head and flew him to Guantánamo. Since his release three years ago, Mr. Boumediene, an Algerian by birth, has lived anonymously in the south of France, quietly enraged but determined to start anew and to resist the pull of that anger.

He calls Guantánamo a “black hole.” Islam carried him through, he says. In truth, though, he still cannot escape it, and is still racked by questions. “I think back over everything in my life, all the stages, who my friends were, who I did this or that with, who I had a simple coffee with,” Mr. Boumediene said. “I do not know, even now, why I was at Guantánamo.”

THERE were early accusations of a plot to bomb the American Embassy in Sarajevo; he lived in that city with his family, working for the Red Crescent, the Muslim branch of the Red Cross. President George W. Bush hailed his arrest in a State of the Union address on Jan. 29, 2002.

In time, those accusations disappeared, Mr. Boumediene says, replaced by questions about his work with Muslim aid groups and suggestions that those groups financed Islamic terrorism. According to a classified detainee assessment from April 2008, published by WikiLeaks, investigators believed that he was a member of Al Qaeda and the Armed Islamic Group of Algeria. Those charges, too, later vanished.