AZZAM THE AMERICAN.

Adam Gadahn, the first American to be charged with treason in more than fifty years, was born in Oregon, grew up in rural California, and converted to Islam at the age of seventeen. He is now twenty-eight. No one who knew him before his religious awakening ever thought that he would join Al Qaeda, and many people who knew him after he did are still perplexed. And yet, in a short time, Gadahn has become one of Osama bin Laden's senior operatives. (He is believed to be hiding in the North Waziristan region of Pakistan.) He is a member of Al Qaeda's "media committee," and his responsibilities are thought to include those of translator, video producer, and cultural interpreter. Primarily, though, Gadahn is a spokesperson, a role he performs with tremendous conviction. He has addressed the United States in five videos, most of which reach a wide audience on the Internet and, in some form or another, have been discussed on the evening news. Last year, shortly before the fifth anniversary of September 11th, Al Qaeda's leadership featured Gadahn in a video titled "An Invitation to Islam." The video began with an introduction from Ayman al-Zawahiri, Al Qaeda's main theoretician, who referred to Gadahn tenderly as a brother and as "a perceptive person who wants to lead his people out of darkness into the light." Zawahiri implored his Western audience to listen to Gadahn, even to follow his example. Al Qaeda had never before given one of its members, let alone an American, an endorsement so intimate and direct.

There is a certain stylistic uniformity to all forms of propaganda, but the personality of the propagandist is never far from the surface. Bin Laden's murmuring voice belies the contempt in his words. Zawahiri speaks in the confident, rhythmic clauses of a master strategist. Adam Gadahn, though he tries to adopt the composure of a statesman, exudes the zealotry of a convert, and of youth. Sometimes his syntax is so baroque, his sentiment so earnest, that he sounds like a character from "The Lord of the Rings." "The call has gone out," he proclaimed in one video. "The era of jihad and resistance has dawned in all its glory." Mostly, though, Gadahn sounds angry. In 2005, with his head wrapped in a black turban and his face covered with a black veil, he warned, "We love nothing better than the heat of battle, the echo of explosions, and slitting the throats of the infidels." Last July, while discussing civilian casualties in Iraq, he said, "It's hard to imagine that any compassionate person could see pictures, just pictures, of what the Crusaders did to those children, and not want to go on a shooting spree at the Marines' housing facilities at Camp Pendleton." In a feature-length Al Qaeda documentary that was released on the Internet on September 11, 2006, Gadahn referred to the United States as "enemy soil," and celebrated the September 11th hijackers as "dedicated, strong-willed, highly motivated individuals."

"An Invitation to Islam" allowed Americans to observe Gadahn at length. For nearly forty-five minutes, he urged the people of the United States to discard their myriad religious and political beliefs, adopt an uncompromising form of Islam, and "join the winning side." This time, he wore a pristine white robe and a white turban, and he was seated in what appeared to be a modern office; beside him were a flat-screen Compaq computer monitor, a neat row of books, and a full glass of tea. Gadahn has brown eyes, a prominent brow, and thick brown hair. His skin was tanned. A long beard of tight curls puffed outward along the sides of his full cheeks. He is nearly six feet tall, and is thought to weigh more than two hundred pounds. Gadahn cannot keep his body still when he speaks. He points his finger upward, or wields a copy of the Koran, or swipes his hand in front of his chest to dismiss an erroneous idea. "Time is running out," Gadahn said, waving an arm up and down. "So make the right choice before it's too late and you meet the dismal fate of thousands before you."

Adam Gadahn's nom de guerre is Azzam al-Amriki (Azzam the American). He can fluently recite the Koran in classical Arabic, and, since the late nineteen-nineties, when he joined the jihad, his English has acquired a vaguely Middle Eastern accent. At times, he speaks in what might be called Jihadlish--a peculiar fusion of American vernacular and militant Islamist theory. Gadahn may be the first Al Qaeda operative to lace a religious threat with a reference to Monopoly. ("If you die as an unbeliever in battle against the Muslims, you're going straight to hell, without passing Go.") Or to adopt the bluster of a barroom pundit. ("Whoever takes over for Bush probably won't have the guts to bring the troops home.") Once, referring to Abu Jahal, an early enemy of Islam known as the Father of Ignorance, Gadahn said, "I can't forget the day, when, as I was praying a prescribed prayer with one of the brothers in a shopping-center parking lot in suburban America, a man sped by in his sports-utility vehicle shouting from his open window, 'Worship Jesus, your Lord.' The gas guzzler, cell phone, and college diploma notwithstanding, one couldn't help but be reminded of Abu Jahal in the seventh century, abusing the Prophet while he prayed."

In May, 2004, the F.B.I. announced that Gadahn was wanted for questioning, and in October, 2005, several weeks after he threatened an attack on Los Angeles in a video, the Justice Department indicted him under seal for providing material support to Al Qaeda. Treason was added to that charge in October, 2006, following Zawahiri's endorsement in "An Invitation to Islam" and Gadahn's reference to the United States as "enemy soil." Deputy Attorney General Paul McNulty, who announced the new charge in Washington, stressed that Gadahn had "made a choice" to side with bin Laden. "He chose to join our enemy and to provide it with aid and comfort by acting as a propagandist for Al Qaeda," McNulty said. "Terrorists create fear and intimidation through extreme violence. They want Americans to live and walk in fear. They want to demoralize us. That's why propaganda is so important to them, and why facilitating that propaganda is such an egregious crime." Gadahn's name was added to the government's list of most-wanted terrorists, and a million-dollar bounty was offered for information leading to his capture.

Gadahn is the ultimate "homegrown"--a term used by scholars and government officials for Western citizens who are "picking up the sword of the idea," as one senior F.B.I. official put it, and are willing to attack their own societies, even martyr themselves if required. Most homegrowns are second- or third-generation Muslims, but a few--and perhaps the most puzzling--are converts. Jose Padilla (the so-called Dirty Bomber) and Richard Reid (the so-called Shoe Bomber) are well-known examples. In 2004, Ryan Anderson, a Muslim convert in the Washington Army National Guard, was convicted of attempting to provide Al Qaeda with military intelligence. (During a military sting, Anderson said, "I wish to defect from the United States. I wish to join Al Qaeda, train its members, and conduct terrorist attacks.") John Walker Lindh, who grew up in Marin County, California, never plotted against America, but he joined and fought for the Taliban.

Homegrowns in the United States are especially rare and are poorly understood; most of the scholarship about them is only a few years old. And yet, because of their cultural literacy, and because of the mobility that their citizenship provides, they are potentially the most dangerous of terrorists. This fear has recently propelled a small number of specialists to search for a pattern behind homegrown radicalization and recruitment. Their research has led them to examine the sociology of cults, the psychology of fanaticism, even the formation of defunct political terror groups like West Germany's Red Army Faction. Adam Gadahn's transformation into Azzam al-Amriki may turn out to be a valuable case study in this effort. "The thing that concerns me with Adam Gadahn's situation is, how did it happen?" Randy Parsons, who ran the F.B.I.'s counterterrorism division in Los Angeles from 2002 to 2006, told me. "How did he convert, not to Islam, because obviously what he is into is not mainstream Islam, but to a particularly virulent, violent, radical view of Islam? How does somebody get to that?"