For nearly a decade, a former Al Qaeda operative named Jamal Ahmed al-Fadl has been living in the United States government’s witness-protection program, under an assumed identity. A Sudanese citizen and a onetime confidant of Osama bin Laden’s, Fadl is expected to serve as a central witness in the prosecutions of at least two suspected terrorists being held at the U.S. detention facility in Guantánamo Bay, Cuba. Fadl, a dark-skinned man with close-cropped hair and a mischievous smile, entered government custody in 1996, after walking into the U.S. Embassy in Eritrea and confessing to membership in Al Qaeda. Since then, he has lived in at least half a dozen American towns. (He spent the first eighteen months in a Residence Inn in New Jersey, guarded by several armed F.B.I. agents; subsequently, his wife and children joined him in America, and the family was transferred to a series of undisclosed locations.) Fadl, who is now in his forties, is arguably the United States’ most valuable informant on Al Qaeda; he has provided crucial intelligence about the group’s operations and has made positive identifications of suspected members. At the same time, Fadl—an incessant troublemaker who is known to a small group of F.B.I. agents simply as Junior—has tried the patience of the officials in whose care he resides. “Junior’s a problem child,” Jack Cloonan, a former special agent for the F.B.I., who is now the president of a crisis-management firm, says.

Fadl’s only public appearance to date as a state’s witness occurred in Manhattan in 2001, eight months before the September 11th attacks on the Pentagon and the World Trade Center. Fadl, who was identified only as “Confidential Source 1,” spoke for several days, and his testimony proved critical in the conviction of four Al Qaeda associates who were being tried for their roles in the 1998 bombings of the U.S. Embassies in Kenya and Tanzania, which killed two hundred and twenty-four people. Photographers and courtroom artists were forbidden to depict his face, but reporters described him as testifying calmly in heavily accented English and wearing a white skullcap, an open-collared shirt, and jeans.

According to Fadl, he met bin Laden in Afghanistan, where he had gone in his early twenties to fight against the Soviet Union. He testified that he was one of the first people to join Al Qaeda, in 1989; soon afterward, he moved back to Sudan, where he helped bin Laden acquire properties and front companies. At a time when most Americans knew little about Al Qaeda, Fadl provided the jury with a lengthy tutorial, describing the organization’s cellular structure and its training camps, where recruits learned how to handle weapons and were taught a militant view of Islam. He characterized bin Laden as a man determined to attack the United States—even with nuclear weapons if he could. In the early nineties, he testified, bin Laden issued a secret fatwa at a meeting in Sudan: “It say, ‘We cannot let the American army stay in the Gulf area and take our oil, take our money, and we have to do something to take them out. We have to fight them.’ ” (Fadl also admitted to a life style that was less than pious. Under questioning, he confessed that, prior to joining Al Qaeda, he had nearly been arrested for smoking marijuana with a friend, on a trip to Saudi Arabia; the friend had gone to jail for two years, he said, adding, “I escaped to Sudan.”) In the end, the four Embassy-bombing suspects were convicted on three hundred and two terrorism-related charges, and were given life sentences.

According to the F.B.I., Fadl has continued to provide assistance to government officials working to understand and combat Al Qaeda. Dan Coleman, a senior consultant at Harbinger Technologies Group, who was the F.B.I.’s top specialist on Al Qaeda until 2004, when he retired, said of Fadl, “He’s been very, very important to us. When it comes to understanding Al Qaeda, he’s the Rosetta stone.” Jessica Stern, a terrorism scholar at Harvard, says that Fadl’s testimony in the Embassy-bombing trials created an invaluable public record. “Fadl explained the nature of the enemy to us when we knew very little,” she said. “He showed us that bin Laden was like any other C.E.O., and that Al Qaeda was a real bureaucracy.” (Fadl had explained, for example, that Al Qaeda’s main advisory council, the majlis al-shura, functioned much like a board of directors.) Michael Anticev, an F.B.I. special agent on the New York-based Joint Terrorism Task Force, told me that as soon as U.S. authorities started to interrogate him “we realized we had struck gold.” He went on, “He spoke to us in great detail, and everything that he told us panned out.” Anticev likened Fadl’s value to that of Joseph Valachi, the government informant on organized crime who, in 1962, became the first member of the Mafia to acknowledge its existence to law-enforcement officials.

In the immediate aftermath of the September 11th attacks, Fadl proved disappointingly unable to shed light on the plot. He had been out of Al Qaeda for too long, and knew none of the hijackers. But, a few months later, when the F.B.I. showed him photographs of prisoners who had been captured on the battlefields of Afghanistan and transferred to Guantánamo, “he went right to work,” Anticev told me. Fadl was shown photographs of between sixty and seventy detainees. F.B.I. sources say that he recognized two men as longtime Al Qaeda figures. L’Houssaine Kherchtou, another former Al Qaeda member interviewed by the agency—and known to U.S. officials as Joe the Moroccan—corroborated Fadl’s claims. Kherchtou, a Moroccan citizen who became an informant after the Embassy bombings, is also in the U.S. witness-protection program. (American law-enforcement officials declined to say how many former terrorists are in the program, but the number is believed to be extremely small.)

Three F.B.I. agents flew to Guantánamo and tried to get both suspects to confess. They succeeded with one of them; the other is still being investigated. Information from Fadl eventually anchored one of only seven formal claims of criminality that the U.S. government has so far been able to make against the Guantánamo detainees, who still number more than four hundred. The prosecutions have been stymied by protracted arguments about the constitutionality of the Bush Administration’s effort to try terrorist suspects not in courtrooms but before military commissions. In June, the Supreme Court ruled, in Hamdan v. Rumsfeld, that the commissions system was illegal.

The F.B.I. has declined to disclose the name of either Guantánamo suspect, for fear of jeopardizing any eventual prosecution. But a close look at government records reveals that Fadl’s name appears as a co-conspirator in a document enumerating the charges against a detainee named Ibrahim Ahmed Mahmoud al-Qosi—also known by the aliases Mohammed Salih Ahmed and Abu Khobaib al-Sudani. According to the document, Qosi is charged with conspiring with Al Qaeda; between 1992 and 1995, he allegedly served as a financial accountant and treasurer for a Sudanese front company, run by bin Laden, which raised money and procured weapons for terrorist operations. Qosi is also accused of serving as a bodyguard, driver, and cook for bin Laden in Afghanistan. According to the charges, Qosi was captured after helping other Al Qaeda members flee Kandahar in the wake of the September 11th attacks.

Another indication that Fadl is an informant behind the charges is that the document names Fadl’s brother-in-law Mohammed Suliman al-Nalfi as an additional co-conspirator. In 2000, four years after acknowledging his own role in Al Qaeda, Fadl led U.S. officials to Nalfi, an Al Qaeda member in Kenya. Authorities had hoped to recruit Nalfi, who was close to Al Qaeda’s co-founder, the Egyptian Ayman al-Zawahiri, as a double agent. But when he proved resistant U.S. officials arrested him and brought him to America, where he eventually pleaded guilty to terrorist-related activities; in 2003, he was sentenced to ten years in prison.

Since September 11, 2001, the Bush Administration has often characterized criminal law-enforcement approaches to fighting terrorism as inadequate and obsolete, and assigned the principal responsibility for fighting Al Qaeda to the military. But Fadl’s role in convicting terrorists and bolstering indictments suggests, to some experts, that the government needs to devote more resources to law-enforcement efforts that yield solid eyewitness testimony. This is especially true, they say, in the wake of the Hamdan decision, which will likely result in Al Qaeda suspects being tried under more conventional rules, where the evidentiary burden is high. Cloonan said, “If your intent is to prosecute somebody, there are rules and regulations that you have to follow—the federal rules of criminal procedure.” He acknowledged that the legal system wasn’t perfect: “I’m not going to tell you that this isn’t cumbersome and slow and plodding at points.” Nevertheless, he said, his experience with Fadl and other informants has taught him that the American legal system is “set up very well to handle these kinds of cases.”

At the 2001 Embassy-bombings trials, defense lawyers revealed that, since 1997, Fadl had received nearly a million dollars from the U.S. government, in the form of housing, food, medical care, and other subsidies. He has also required the oversight of F.B.I. agents, who have lived with him in one safe house after another. Mike Anticev, Fadl’s designated handler, has spent the most time with the former terrorist. Sitting at a small conference table earlier this month at the F.B.I.’s headquarters in lower Manhattan, Anticev, a powerfully built man with high cheekbones and brown eyes, said that keeping Fadl and taking care of him have been “absolutely worth it for the government. Junior wrote the book on Al Qaeda, and the well still isn’t dry.” He paused. “But for me? What a lot of headaches! I have a very good relationship with him, but he’s a full-time job. I’m his big brother, his coach, his psychiatrist, and his marriage counsellor. If he has trouble with his family, I’m almost like a parent—I have to be the bearer of bad news. At times, I spend hours a day on the phone. Weekends. Nights. Whatever the problem of the day is, I have to deal with it.”

Anticev’s cell phone rang. He glanced at the phone’s display and sighed. “That’s him,” he said. He normally answers Fadl’s calls immediately, but this time he let him leave a message.

Dan Coleman, the former Al Qaeda specialist at the F.B.I., spent many hours debriefing Fadl. “He’s a lovable rogue,” he said. “He’s fixated on money. And he loves women.” U.S. officials allegedly exploited the latter enthusiasm during Fadl’s initial interrogations, in order to cement his loyalty. Fadl told two counterterrorism officials that, while he was being debriefed by the C.I.A. in Eritrea, the agency provided him with free housing, which he shared with a “girlfriend.” Later, one of the officials said, Fadl “used to carry a photograph” of the woman, and cried about having left her behind. A former C.I.A. official, who was involved with Fadl’s case at the time, denied this, saying, “There was no girlfriend I knew of in Eritrea.”

At first, Fadl was reluctant to speak freely on various personal matters, in particular his reasons for breaking with bin Laden. But he provided a surprisingly full picture of Al Qaeda, depicting it as an international criminal network intent on attacking the United States. Fadl said that he had handled many of Al Qaeda’s financial transactions after bin Laden left Afghanistan and moved the hub of his operations to Khartoum, in 1992. In this role, Fadl had access to bin Laden’s payroll and knew the details of Al Qaeda’s global banking networks, its secret membership lists, and its paramilitary training camps in Afghanistan, one of which he had attended, in the late eighties. Two years before the Embassy bombings in East Africa, Fadl warned U.S. officials that bin Laden’s followers might try to attack U.S. embassies abroad or targets inside America.

His story astounded U.S. officials. Anticev recalled, “In the beginning, it was hard to get your arms around how big this conspiracy really was and how many people were involved. There were all of these players, and a global organization of all these different terrorist groups. He told us about all the different committees, and about bin Laden himself.” Fadl described bin Laden as soft-spoken, and said that he had a good sense of humor. He noted that one Al Qaeda member, Abu Rida al-Suri, was unusually witty and frequently made bin Laden laugh—a description that was borne out when Anticev had a chance to talk to Suri, in Khartoum. Fadl displayed a firm command of Al Qaeda’s financial structure, and asserted that it resembled that of an international conglomerate. Bin Laden’s business decisions hadn’t always pleased him, however. Among other things, he said that jihadis from Egypt were often paid better and given more responsibility than those from other countries. Fadl complained to bin Laden bitterly about this, but his plea for equal pay and equal work was rejected.

Fadl told U.S. officials, and later testified in court, that he had been charged with exploring the possibility of purchasing uranium—Al Qaeda, he said, had been interested in obtaining nuclear and chemical weapons. And he revealed tradecraft secrets, explaining that Al Qaeda operatives were taught to disguise their identities by appearing Western—shaving beards, wearing cologne, and carrying cigarettes—and never discussing jihad in public.

C.I.A. officials debriefed Fadl for a month and a half. In the fall of 1996, the C.I.A. flew him from Eritrea to a U.S. military base in Germany, where he entered the custody of the F.B.I. The C.I.A. also handed over transcripts of its interviews with Fadl. (The smooth coöperation between the two agencies in this case contradicts the widespread notion that the C.I.A. and the F.B.I. were incapable of working together.) Dan Coleman interrogated Fadl at the base. At first, Fadl claimed that his motives for talking were an interest in writing a tell-all book and a love for the United States. (He had lived in America for two years in the mid-eighties, primarily in Brooklyn and in Atlanta, learning English and working in various delis and grocery stores.) After a week or so, Coleman coaxed him into admitting that his real reason for breaking with Al Qaeda was that he had skimmed a large sum of money from bin Laden’s business ventures. He had stolen more than a hundred thousand dollars, and he knew that bin Laden wouldn’t forgive him. Coleman said that, in his experience, the hardest story to get from any suspect is a narrative in which he incriminates himself. “We had to know everything, warts and all, if he was going to be a witness,” Coleman recalled. “It caused tears and gnashing of teeth. He thought we’d think less of him. He was ashamed.” At the same time, Coleman said, “he likes to please. Most people do.” Coleman said that he got Fadl to confess through persistence and persuasion, not through threats or violence. (Cloonan, the former special agent, said that the same was true for Kherchtou, the Moroccan informant, who was persuaded to coöperate while enjoying three-course meals at a large Moroccan estate.)

Coleman was surprised to learn that Fadl wasn’t particularly religious. “I never saw him pray once,” he said. For Fadl, jihad was less a spiritual quest than “a socially acceptable form of bad behavior.” As Coleman put it, “You get to blow stuff up and kill people, and your colleagues and peers think you’re good. It’s fun, and you can be a hero.” Coleman acknowledged that most Al Qaeda members were deeply committed to Islam, but he said that it had been a breakthrough to realize that some were more like ordinary criminals, and could be manipulated in ways familiar to law-enforcement officials. (Kherchtou was a pilot who worked for bin Laden for money, and he was angered when Al Qaeda refused to pay for his wife’s Cesarean-section operation.)

The F.B.I. used the information provided by Fadl to strengthen a criminal indictment that was being drawn up against bin Laden by Mary Jo White, the U.S. Attorney in New York. Before the government acquired Fadl as a witness, prosecutors had worried that the legal case against bin Laden might be hard to make. Cloonan recalled, “All of a sudden, out of nowhere, comes this Junior. It was something. He’s telling you how they work, what they were planning, how they recruit. . . . His life story becomes the spine of the prosecution—a walking, talking body who will sit up on the witness stand and look the jury in the eye. This is powerful stuff!” In 1998, the indictment was completed. It charged bin Laden with running a terrorist organization that, among other things, had played a role in the 1993 attack on American troops in Mogadishu, Somalia, and had bombed the U.S. Embassies in East Africa.

The Justice Department worked out a plea agreement with Fadl that would keep him in its custody but out of jail, at least for the time being. Fadl pleaded guilty to two terrorism-related charges, stemming from his help in smuggling weapons for bin Laden. He faced up to fifteen years in prison, depending upon how helpful he proved to be. Because he has continued to assist U.S. authorities, he has yet to be sentenced, and may never be.

Soon after the F.B.I. took custody of Fadl, agents realized that his scheming, which had once been bin Laden’s problem, was now theirs. Cloonan says of Fadl, “For one thing, he’s a gambler.” He recalled that Fadl once won a modest sum in a New Jersey lottery, after persuading his overseers to let him play the scratch-off cards at a 7-Eleven. (The guards confiscated his earnings.) At one point, Fadl persuaded the government to give him a business loan, and he then opened a deli. But financial problems ensued, and the business ran aground. Fadl asked officials again and again for permission to write and publish his memoirs, but they repeatedly turned him down. More recently, he tried unsuccessfully to get permission to go to Sudan to claim his share of a family inheritance, following the death of his father. Anticev said that it would be “far too dangerous” for Fadl to return home, because he would likely be killed by former comrades-in-arms.

Cloonan said that Fadl’s pursuit of women had posed numerous perils. “The last thing we wanted was for him to get involved with women,” he said. “What would the court think? It would blow his cover!” The F.B.I. agents recalled Fadl flirting with female agents and young female lifeguards at the swimming pool of the New Jersey hotel where he was staying before his wife’s arrival. “He’s a very outgoing guy,” Cloonan said. “He was like a heat-seeking missile.” He went on, “He didn’t know how to swim, so we got him some noodles. We loved to just watch Junior floating around the pool and making a fool of himself. He was, like, the mayor of the motel.” He discovered other pleasures of American life. “Waffles!” Cloonan said. “Junior absolutely loved them. He ordered them for breakfast every day. If you ate like him, you’d have gained fifty pounds.”

Fadl loves sports, and, to keep him busy, the F.B.I. gave him money to buy a Ping-Pong table. His favorite game, however, is soccer, and when he lived in New Jersey he begged the agents to let him coach a local girls’ team. Permission was denied.

“It was to our advantage to let him blow off steam,” Cloonan explained. “It made him feel more like a human being than a prisoner. You have to worry about mood swings. Sometimes he’d have trouble sleeping. At three in the morning on a winter’s night, you’d counsel him. ‘I’m a traitor,’ he’d say. ‘I miss my wife.’ You’re always concerned about someone’s mental state.” As time wore on, and Fadl complained increasingly of loneliness, the F.B.I. helped find his wife, Nadia, and their four children, in Khartoum, and brought them to the United States. Cloonan witnessed the reunion, and was quietly disappointed. “We thought they’d be running at each other,” he recalled. “Instead, they just looked at each other, and it was, like, ‘Oh, hi. How are you?’ ”

Coleman said that the domestic tensions rapidly escalated. “Nadia would really break Junior’s chops, unmercifully,” he said. “She basically did nothing but complain from the time she arrived in the U.S.” There were numerous cultural conflicts. When the agents gave her lobsters as a Fourth of July treat, she accused them of trying to poison her family with “water spiders.” Once, she cooked dinner for them, placing a pigeonlike bird directly over the burners of a gas stove. “It was brutal,” Cloonan said, but he added that he politely ate his meal. When Nadia first arrived, Fadl asked to have her undergo a ritual cleansing that involved covering her in mud and then placing her over warm embers in a back-yard pit. “Suffice it to say that we did not allow Junior to smoke Nadia in a pit,” Cloonan said.

Although Nadia did not learn English or adapt to American culture as easily as her husband, she happily returned from a trip to a department store—sponsored by the F.B.I., which wanted her to have more American-looking clothes—with a pair of pink-and-white L.A. Gear sneakers. She also proved to be a better softball player than Fadl. (When he sulked after being humiliated in a game, she shook her finger at him and said, “I’m in America now. I have rights!”) At the urging of several female agents, she even consented, despite her strict Muslim background, to remove her veil and get her hair done at a salon, along with a manicure and pedicure. When she showed off her new look, several agents applauded while Cloonan announced on the P.A. system of his F.B.I. car, “Now, for the first time in public, Mrs. Nadia al-Fadl!”

But the agents who took turns living with the couple said that Nadia was overwhelmed by taking care of four children without help from relatives. “She wanted her grandmother, her mother, her sisters, and her sisters’ children,” Coleman said. “She was used to a huge extended family. In Sudan, basically, what people do from the moment they get up in the morning is talk. And she didn’t have anybody to talk to but him. And the kids were underfoot.”

In the late nineties, the F.B.I. imported eight more relatives. Nadia wanted them all to live in the same house, but the Marshals Service, which oversees the protection of government witnesses, couldn’t deal with the security issues. Instead, the extended family was housed nearby. But soon, the agents said, some relatives began to complain that it was haram—forbidden by Islam—for Fadl to be coöperating as a witness with the U.S. government. The discontent spread, and the relatives had to be sent back to Africa.

Fadl’s older children spoke only Arabic, and they were provided with tutors for their schooling. Soon they were playing American sports and begging for trips to McDonald’s and water parks. But the process of assimilation was bumpy. At one point, when a supermarket-checkout person stared suspiciously at the agents and the Fadl family, the agents explained that they were “missionaries” and that the Fadls were converts. Cloonan recalled that the checkout person was overcome with admiration, offering to do anything she could to help the family.

Fadl has occasionally had trouble keeping his identity and whereabouts a secret. Once, after being stopped for speeding by a state trooper, he tried to get out of the situation by announcing that he knew Osama bin Laden personally. Another time, during a secure videoconference, Fadl mentioned that it was snowing outside his window; the Marshals Service severely reprimanded him for the slip.

Nadia has chafed at the boundaries of life in the witness-protection program, and has periodically threatened to return to Sudan. Two years ago, on a Sunday night in the middle of the summer, Anticev received a call from Fadl. “He said that Nadia was leaving, and that she’d taken the kids on a Greyhound bus to New York. He was crying, and asking me, ‘What do I do?’ ” Soon afterward, Anticev received a call from Nadia, who was at the Port Authority. He met her and the children at the F.B.I.’s headquarters in lower Manhattan, and persuaded her to go back home.

A prime source of marital trouble, Anticev said, has been Fadl’s desire for other women. Not long ago, Anticev declined Fadl’s request to marry a second wife. Fadl argued that the American government had promised to support his entire family. He reminded Anticev that, under his agreement with the authorities, his family was defined as anyone he loved. He swore that he loved this new woman. Back in the eighties, in America, Fadl had briefly married a second wife, without telling her about Nadia; this time, Anticev said, “I told him I was responsible for the well-being of his wife and kids, and I didn’t see another wife as in their interest.”

Although the U.S. government draws the line at polygamy, the F.B.I. agents say they are happy to publicize the fact that they have been giving the former Al Qaeda operative considerable financial support for the past ten years. The government even paid hundreds of thousands of dollars in hospital bills when one of Fadl’s children required heart surgery. “It’s what you have to do,” Anticev said. “And it’s a good story to put out. If you’ve got valuable information, we’ll do what we can to help.”

Anticev, Cloonan, and Coleman—three men who have spent countless hours debriefing Al Qaeda operatives—all take issue with the kinds of rough interrogations that have characterized the Bush Administration’s approach since September 11th. Anticev says, “Just building a relationship with a person, and knowing your subject matter, is what works.”

Coleman, for his part, believes that “people don’t do anything unless they’re rewarded.” He says that if the F.B.I. had beaten a confession out of Fadl with what he calls “all that alpha-male shit,” it would never be able to talk to him now. Brutality may yield a timely scrap of information, he conceded. But in the longer fight against terrorism such an approach is “completely insufficient,” he says. “You need to talk to people for weeks. Years.”

Cloonan, too, is a skeptic about the Bush Administration’s commands to handle terrorism suspects roughly. (In 2001, Vice-President Cheney declared that it was time for the U.S. to enter “sort of the dark side.”) Few suspects, he acknowledged, are as eager to confess as Fadl was. Nevertheless, he suggested, there is always the possibility that other people with useful information about Al Qaeda will consider becoming informants. “You think all of this stuff about torture is going to make people want to come to us?” Cloonan asked. “That’s why I get upset when I hear people talking about stress positions, loud music, and dogs.” Looking back, he said, “There’s a lot of stuff Junior talked about in casual, non-threatening moments.” He smiled. “You could talk about everything with Fadl. That’s the beauty of it.” ♦