The legend of John P. O'Neill, who lost his life at the World Trade Center on September 11th, begins with a story by Richard A. Clarke, the national coördinator for counter-terrorism in the White House from the first Bush Administration until last year. On a Sunday morning in February, 1995, Clarke went to his office to review intelligence cables that had come in over the weekend. One of the cables reported that Ramzi Yousef, the suspected mastermind behind the first World Trade Center bombing, two years earlier, had been spotted in Pakistan. Clarke immediately called the F.B.I. A man whose voice was unfamiliar to him answered the phone. "O'Neill," he growled.

"Who are you?" Clarke said.

"I'm John O'Neill," the man replied. "Who the hell are you?"

O'Neill had just been appointed chief of the F.B.I.'s counter-terrorism section, in Washington. He was forty-two years old, and had been transferred from the bureau's Chicago office. After driving all night, he had gone directly to headquarters that Sunday morning without dropping off his bags. When he heard Clarke's report about Yousef, O'Neill entered the F.B.I.'s Strategic Information Operations Center (SIOC) and telephoned Thomas Pickard, the head of the bureau's National Security Division in New York. Pickard then called Mary Jo White, the United States Attorney for the Southern District of New York, who had indicted Yousef in the bombing case.

One of O'Neill's new responsibilities was to put together a team to bring the suspect home. It was composed of agents who were working on the case, a State Department representative, a medical doctor, a hostage-rescue team, and a fingerprint expert whose job was to make sure that the suspect was, in fact, Ramzi Yousef. Under ordinary circumstances, the host country would be asked to detain the suspect until extradition paperwork had been signed and the F.B.I. could place the man in custody. There was no time for that. Yousef was reportedly preparing to board a bus for Peshawar. Unless he was apprehended, he would soon cross the Khyber Pass into Afghanistan, where he would be out of reach. There was only one F.B.I. agent in Pakistan at the time, along with several agents from the Drug Enforcement Administration and the State Department's diplomatic-security bureau. "Our Ambassador had to get in his car and go ripping across town to get the head of the local military intelligence," Clarke recalled. "The chief gave him his own personal aides, and this ragtag bunch of American law-enforcement officials and a couple of Pakistani soldiers set off to catch Yousef before he got on the bus." O'Neill, working around the clock for the next three days, coördinated the entire effort. At 10 A.M. Pakistan time, on Tuesday, February 7th, SIOC was informed that the World Trade Center bomber was in custody.

During the next six years, O'Neill became the bureau's most committed tracker of Osama bin Laden and his Al Qaeda network of terrorists as they struck against American interests around the world. Brash, ambitious, often full of himself, O'Neill had a confrontational personality that brought him powerful enemies. Even so, he was too valuable to ignore. He was the point man in the investigation of the terrorist attacks in Saudi Arabia, East Africa, and Yemen. At a time when the Clinton Administration was struggling to decide how to respond to the terrorist threat, O'Neill, along with others in the F.B.I. and the C.I.A., realized that Al Qaeda was relentless and resourceful and that its ultimate target was America itself. In the last days of his life, after he had taken a new job as the chief of security for the World Trade Center, he was warning friends, "We're due."

"I am the F.B.I.," John O'Neill liked to boast. He had wanted to work for the bureau since boyhood, when he watched Efrem Zimbalist, Jr., as the buttoned-down Inspector Lewis Erskine in the TV series "The F.B.I." O'Neill was born in 1952 and brought up in Atlantic City, where his mother drove a cab for a small taxi business that she and his father owned. After graduating from Holy Spirit High School, he got a job as a fingerprint clerk with the F.B.I. During his first semester in college, he married his high-school sweetheart, Christine, and when he was twenty their son, John P. O'Neill, Jr., was born. O'Neill put himself through a master's program in forensics at George Washington University by serving as a tour guide at the F.B.I. headquarters. In 1976, he became a full-time agent in the bureau's office in Baltimore; ten years later, he returned to headquarters and served as an inspector. In 1991, he was named assistant special agent in charge in the Chicago office. In 1994, he received the additional assignment of supervising VAPCON, a national investigation into violence against abortion providers. The following year, he transferred to headquarters to become the counter-terrorism chief.

John Lipka, an agent who met O'Neill during the VAPCON probe, marvelled at his ability to move so easily from investigating organized crime and official corruption to the thornier field of counter-terrorism. "He was a very quick study," Lipka told me. "I'd been working terrorism since '86, but he'd walk out of the Hoover building, flag a cab, and I'd brief him on the way to the White House. Then he'd give a presentation, and I'd be shocked that he grasped everything I had been working on for weeks."

O'Neill entered the bureau in the J. Edgar Hoover era, and throughout his career he had something of the old-time G-man about him. He talked tough, in a New Jersey accent that many loved to imitate. He was darkly handsome, with black eyes and slicked-back hair. In a culture that favors discreet anonymity, he cut a memorable figure. He favored fine cigars and Chivas Regal and water with a twist, and carried a nine-millimetre automatic strapped to his ankle. His manner was bluff and dominating, but he was always immaculately, even fussily, dressed. One of his colleagues in Washington took note of O'Neill's "night-club wardrobe"—black double-breasted suits, semitransparent black socks, and ballet-slipper shoes. "He had very delicate feet and hands, and, with his polished fingernails, he made quite an impression."

In Washington, O'Neill became part of a close-knit group of counter-terrorism experts which formed around Richard Clarke. In the web of federal agencies concerned with terrorism, Clarke was the spider. Everything that touched the web eventually came to his attention. The members of this inner circle, which was known as the Counter-terrorism Security Group (C.S.G.), were drawn mainly from the C.I.A., the National Security Council, and the upper tiers of the Defense Department, the Justice Department, and the State Department. They met every week in the White House Situation Room. "John could lead a discussion at that level," R. P. Eddy, who was an N.S.C. director at the time, told me. "He was not just the guy you turned to for a situation report. He was the guy who would say the thing that everybody in the room wishes he had said."

In July of 1996, when T.W.A. Flight 800 crashed off the coast of Long Island, there was widespread speculation in the C.S.G. that it had been shot down by a shoulder-fired missile from the shore. Dozens of witnesses reported having seen an ascending flare that culminated in an explosion. According to Clarke, O'Neill, working with the Defense Department, determined the height of the aircraft and its distance from shore at the time of the explosion, and demonstrated that it was out of the range of a Stinger missile. He proposed that the flare could have been caused by the ignition of leaking fuel from the aircraft, and he persuaded the C.I.A. to do a video simulation of this scenario, which proved to be strikingly similar to the witnesses' accounts. It is now generally agreed that mechanical failure, not terrorism, caused the explosion of T.W.A. Flight 800.

Clarke immediately spotted in O'Neill an obsessiveness about the dangers of terrorism which mirrored his own. "John had the same problems with the bureaucracy that I had," Clarke told me. "Prior to September 11th, a lot of people who were working full time on terrorism thought it was no more than a nuisance. They didn't understand that Al Qaeda was enormously powerful and insidious and that it was not going to stop until it really hurt us. John and some other senior officials knew that. The impatience really grew in us as we dealt with the dolts who didn't understand."

Osama bin Laden had been linked to terrorism since the first World Trade Center bombing, in 1993. His name had turned up on a list of donors to an Islamic charity that helped finance the bombing, and defendants in the case referred to a "Sheikh Osama" in a recorded conversation. "We started looking at who was involved in these events, and it seemed like an odd group of people getting together," Clarke recalled. "They clearly had money. We'd see C.I.A. reports that referred to 'financier Osama bin Laden,' and we'd ask ourselves, 'Who the hell is he?' The more we drilled down, the more we realized that he was not just a financier—he was the leader. John said, 'We've got to get this guy. He's building a network. Everything leads back to him.' Gradually, the C.I.A. came along with us."

O'Neill worked with Clarke to establish clear lines of responsibility among the intelligence agencies, and in 1995 their efforts resulted in a Presidential directive giving the F.B.I. the lead authority both in investigating and in preventing acts of terrorism wherever Americans or American interests were threatened. After the April, 1995, bombing in Oklahoma City, O'Neill formed a separate section for domestic terrorism, but he concentrated on redesigning and expanding the foreign-terrorism branch. He organized a swap of deputies between his office and the C.I.A.'s counter-terrorism center, despite resistance from both agencies.

"John told me that if you put the resources and talents of the C.I.A.'s counter-terrorism center and the F.B.I.'s counter-terrorism section together on any issue, we can solve it—but we need both," Lipka recalled. In January, 1996, O'Neill helped create a C.I.A. station, code-named Alex, with a single-minded purpose. "Its mission was not just tracking down bin Laden but focussing on his infrastructure, his capabilities, where he got his funding, where were his bases of operation and his training centers," Lipka said. "Many of the same things we are doing now, that station was already doing then."

The coöperation that O'Neill achieved between the bureau and the C.I.A. was all the more remarkable because opinions about him were sharply polarized. O'Neill could be brutal, not only with underlings but also with superiors when they failed to meet his expectations. An agent in the Chicago office who felt his disapproval told me, "He was smarter than everybody else, and he would use that fine mind to absolutely humiliate people."

In Washington, there was one terrorist-related crisis after another. "We worked a bomb a month," Lipka recalled. Often, O'Neill would break for dinner and be back in the office at ten. "Most people couldn't keep up with his passion and intensity," Lipka said. "He was able to identify those people who shared his work ethic, and then he tasked the living shit out of them, with E-mails and status briefings and phones and pagers going off all the time, to the point that I asked him, 'When do you sleep?' " O'Neill began acquiring nicknames that testified to his relentlessness, among them the Count, the Prince of Darkness, and Satan.

But many in the bureau who disliked O'Neill eventually became devoted followers. He went to extraordinary lengths to help when they faced health problems or financial difficulty. "He was our Elvis—you knew when he was in the house," Kevin Giblin, the F.B.I.'s head of terrorist warning, recalled.

O'Neill's tenure in the F.B.I. coincided with the internationalization of crime and law enforcement. Prior to his appointment as the bureau's counter-terrorism chief, the F.B.I. had limited its involvement to operations in which Americans had been killed. "O'Neill came in with a much more global approach," Lipka told me. One of his innovations was to catalogue all the explosives used by terrorists worldwide. "He thought, When a bomb goes off in the Egyptian Embassy in Islamabad, even though no Americans were killed, why don't we offer our assistance, so that we can put that information on a global forensic database," Lipka said. Since 1984, the F.B.I. had had the authority to investigate crimes against Americans abroad, but that mandate had been handicapped by a lack of coöperation with foreign police agencies. O'Neill made a habit of entertaining every foreign cop or intelligence agent who entered his orbit. He called it his "night job."

"John's approach to law enforcement was that of the old Irish ward boss to governance: you collect friendships and debts and obligations, because you never know when you're going to need them," Clarke told me. He was constantly on the phone, doing favors, massaging contacts. By the time he died, he had become one of the best-known policemen in the world. "You'd be in Moscow at some bilateral exchange," Giblin recalled, "and you'd see three or four men approach and say, in broken English, 'Do you know John O'Neill?' "

The need to improve relationships with foreign police agencies became apparent in November, 1995, when five Americans and two Indians died in the bombing of an American-run military-training center in Riyadh, Saudi Arabia. The F.B.I. sent over a small squad to investigate, but the agents had scarcely arrived when the Saudis arrested four suspects and beheaded them, foreclosing any opportunity to learn who was behind the operation.

In the spring of 1996, Jamal Ahmed al-Fadl, who had supported a plot by Al Qaeda against American soldiers in Somalia four years earlier, arrived at the American Embassy in Asmara, Eritrea. The C.I.A. debriefed him for six months, then turned him over to the F.B.I., which put him in the witness-protection program. Fadl provided the first extensive road map of the bin Laden terrorist empire. "Fadl was a gold mine," an intelligence source who was present during some of the interviews told me. "He described the network, bin Laden's companies, his farms, his operations in the ports." Fadl also talked about bin Laden's desire to attack Americans, including his ambition to obtain uranium. The news was widely circulated among members of the intelligence community, including O'Neill, and yet the State Department refused to list Al Qaeda as a terrorist organization.

On June 25, 1996, O'Neill arranged a retreat for F.B.I. and C.I.A. agents at the bureau's training center in Quantico, Virginia. "We had hot dogs and hamburgers, and John let the C.I.A. guys on the firing range, because they never get to shoot," Giblin recalled. "Then everyone's beeper went off." Another explosion in Saudi Arabia, at the Khobar Towers, a military-housing complex in Dhahran, had killed nineteen American soldiers and injured more than five hundred other people, including Saudis. O'Neill assembled a team of nearly a hundred agents, support personnel, and members of various police agencies. The next day, they were on an Air Force transport plane to Saudi Arabia. A few weeks later, they were joined by O'Neill and the F.B.I. director, Louis Freeh.

It was evening when the two men arrived in Dhahran. The disaster site was a vast crater illuminated by lights on high stanchions; nearby lay charred automobiles and upended Humvees. Looming above the debris were the ruins of the housing complex. This was the largest bomb that the F.B.I. had ever investigated, even more powerful than the explosives that had killed a hundred and sixty-eight people in Oklahoma City in 1995. O'Neill walked through the rubble, greeting exhausted agents who were sifting the sand for evidence. Under a tarp nearby, investigators were gradually reconstructing fragments of the truck that had carried the bomb.

In the Khobar Towers case, neither the Saudis nor the State Department seemed eager to pursue a trail of evidence that pointed to Iranian terrorists as the likeliest perpetrators. The Clinton Administration did not relish the prospect of military retaliation against a country that seemed to be moderating its anti-Western policies, and, according to Clarke, the Saudis impeded the F.B.I. investigation because they were worried about the American response. "They were afraid that we would have to bomb Iran," I was told by a Clinton Administration official, who added that that would have been a likely course of action.

Freeh was initially optimistic that the Saudis would coöperate, but O'Neill became increasingly frustrated, and eventually a rift seems to have developed between the two men. "John started telling Louis things Louis didn't want to hear," Clarke said. "John told me that, after one of the many trips he and Freeh took to the Mideast to get better coöperation from the Saudis, they boarded the Gulfstream to come home and Freeh says, 'Wasn't that a great trip? I think they're really going to help us.' And John says, 'You've got to be kidding. They didn't give us anything. They were just shining sunshine up your ass.' For the next twelve hours, Freeh didn't say another word to him."

Freeh denies that this conversation took place. "Of course, John and I discussed the results of every trip at that time," he wrote to me in an E-mail. "However, John never made that statement to me. . . . John and I had an excellent relationship based on trust and friendship."

O'Neill longed to get out of Washington so that he could "go operational," as he told John Lipka, and supervise cases again. In January, 1997, he became special agent in charge of the National Security Division in New York, the bureau's largest and most prestigious field office. When he arrived, he dumped four boxes of Rolodex cards on the desk of his new secretary, Lorraine di Taranto. Then he handed her a list of everyone he wanted to meet—"the mayor, the police commissioner, the deputy police commissioners, the heads of the federal agencies, religious and ethnic leaders," di Taranto recalled. Within six months, O'Neill had met everyone on the list.

"Everybody knew John," R. P. Eddy, who left Washington in 1999 for a job at the United Nations, told me. "You would walk into Elaine's or Bruno's with him, and everyone from the owner to the waiters to the guy who cleaned the floor would look up. And the amazing thing is they would all have a private discussion with him at some point. The waitress wanted tickets to a Michael Jackson concert. One of the wait staff was applying for a job with the bureau, and John would be helping him with that. After a night of this, I remember saying, 'John, you've got this town wired.' And he said, 'What's the point of being sheriff if you can't act like one?' "

O'Neill was soon on intimate terms with movie stars, politicians, and journalists—what some of his detractors called "the Elaine's crowd." In the spring of 1998, one of O'Neill's New York friends, a producer at ABC News named Christopher Isham, arranged an interview for a network reporter, John Miller, with Osama bin Laden. Miller's narration contained information to the effect that one of bin Laden's aides was coöperating with the F.B.I. The leak of that detail created, in Isham's words, "a firestorm in the bureau." O'Neill, because of his friendship with Isham and Miller, was suspected of providing the information, and an internal investigation was launched. The matter died down after the newsmen denied that O'Neill was their informant and volunteered to take polygraphs.

In New York, O'Neill created a special Al Qaeda desk, and when the bombings of the American embassies in Kenya and Tanzania occurred, in August, 1998, he was sure that bin Laden was behind them. "He was pissed, he was beside himself," Robert M. Blitzer, who was head of the F.B.I.'s domestic-terrorism section at the time, remembered. "He was calling me every day. He wanted control of that investigation." O'Neill persuaded Freeh to let the New York office handle the case, and he eventually dispatched nearly five hundred investigators to Africa. Mary Jo White, whose prosecuting team subsequently convicted five defendants in the case, told me, "John O'Neill, in the investigation of the bombings of our embassies in East Africa, created the template for successful investigations of international terrorism around the world."

The counter-terrorist community was stunned by the level of coördination required to pull off the simultaneous bombings. Even more troubling was the escalation of violence against civilians. According to Steven Simon, then a terrorist expert at the N.S.C., as many as five American embassies had been targeted—luck and better intelligence had saved the others. It was discouraging to learn that, nearly a year before, a member of Al Qaeda had walked into the American Embassy in Nairobi and told the C.I.A. of the bombing plot. The agency had dismissed this intelligence as unreliable. "The guy was a bullshit artist, completely off the map," an intelligence source said. But his warnings about the impending attacks proved accurate.

Moreover, key members of the Al Qaeda cell that planned the operation had been living in one of the most difficult places in the Western world to gain intelligence: the United States. The F.B.I. is constrained from spying on American citizens and visitors without probable cause. Lacking evidence that potential conspirators were actively committing a crime, the bureau could do little to gather information on the domestic front. O'Neill felt that his hands were tied. "John was never satisfied," one of his friends in the bureau recalled. "He said we were fighting a war, but we were not able to fight back. He thought we never had the tools in place to do the job."

O'Neill never presumed that killing bin Laden alone would be sufficient. In speeches, he identified five tools to combat terrorism: diplomacy, military action, covert operations, economic sanctions, and law enforcement. So far, the tool that had worked most effectively against Al Qaeda was the last one—the slow, difficult work of gathering evidence, getting indictments, hunting down the perpetrators, and gaining convictions.

O'Neill was worried that terrorists had established a beachhead in America. In a June, 1997, speech in Chicago, he warned, "Almost all of the groups today, if they chose to, have the ability to strike us here in the United States." He was particularly concerned that, as the millennium approached, Al Qaeda would seize the moment to dramatize its war with America. The intelligence to support that hypothesis was frustratingly absent, however.

On December 14, 1999, a border guard in Port Angeles, Washington, stopped an Algerian man, Ahmed Ressam, who then bolted from his car. He was captured as he tried to hijack another automobile. In the trunk of his car were four timers, more than a hundred pounds of urea, and fourteen pounds of sulfate—the makings of an Oklahoma City-type bomb. It turned out that Ressam's target was Los Angeles International Airport. The following day, Jordanian authorities arrested thirteen suspected terrorists who were believed to be planning to blow up a Radisson Hotel in Amman and a number of tourist sites frequented by Westerners. The Jordanians also discovered an Al Qaeda training manual on CD-ROM.

What followed was, according to Clarke, the most comprehensive investigation ever conducted before September 11th. O'Neill's job was to supervise the operation in New York. Authorities had found several phone numbers on Ressam when he was arrested. There was also a name, Ghani, which belonged to Abdel Ghani Meskini, an Algerian, who lived in Brooklyn and who had travelled to Seattle to meet with Ressam. O'Neill oversaw the stakeout of Meskini's residence and spent much of his time in the Brooklyn command post. "I doubt he slept the whole month," David N. Kelley, an assistant United States Attorney and chief of organized crime and terrorism for the Southern District, recalled. A wiretap picked up a call that Meskini had made to Algeria in which he spoke about Ressam and a suspected terrorist in Montreal. On December 30th, O'Neill arrested Meskini on conspiracy charges and a number of other suspected terrorists on immigration violations. (Meskini and Ressam eventually became coöperating witnesses and are both assisting the F.B.I.'s investigation of the September 11th attacks.)

O'Neill was proud of the efforts of the F.B.I. and the New York Joint Terrorism Task Force to avert catastrophe. On New Year's Eve, he and his friend Joseph Dunne, then the Chief of Department for the New York City Police, went to Times Square, which they believed was a highly likely target. At midnight, O'Neill called friends at SIOC and boasted that he was standing directly under the giant crystal ball.

After the millennium roundup, O'Neill suspected that Al Qaeda had sleeper cells buried in America. "He started pulling the strings in Jordan and in Canada, and in the end they all led back to the United States," Clarke said. "There was a general disbelief in the F.B.I. that Al Qaeda had much of a presence here. It just hadn't sunk through to the organization, beyond O'Neill and Dale Watson"—the assistant director of the counter-terrorism division. Clarke's discussions with O'Neill and Watson over the next few months led to a strategic plan called the Millennium After-Action Review, which specified a number of policy changes designed to root out Al Qaeda cells in the United States. They included increasing the number of Joint Terrorism Task Forces around the country; assigning more agents from the Internal Revenue Service and the Immigration and Naturalization Service to monitor the flow of money and personnel; and creating a streamlined process for analyzing information obtained from wiretaps.

Many in the F.B.I. point to the millennium investigation as one of the bureau's great recent successes. A year earlier, O'Neill had been passed over when the position of assistant director in charge of national security became available. When the post of chief of the New York office opened up, in early 2000, O'Neill lobbied fiercely for it. The job went to Barry Mawn, a former special agent in charge of the Boston office. As it happened, the two men met at a seminar just after the decision was announced. "I got a knock on the door, and there was John holding two beers," Mawn recalled. O'Neill promised complete loyalty in return for Mawn's support of his work on counter-terrorism. "It turns out that supporting him was a full-time job," Mawn said.

O'Neill had many detractors and very few defenders left in Washington. Despite occasional disagreements, Louis Freeh had always supported O'Neill, but Freeh had announced that he would retire in June, 2001. A friend of O'Neill's, Jerry Hauer, of the New York-based security firm Kroll, told me that Thomas Pickard, who had become the bureau's deputy director in 1999, was "an institutional roadblock." Hauer added, "It was very clear to John that Pickard was never going to let him get promoted." Others felt that O'Neill was his own worst enemy. "He was always trying to leverage himself to the next job," Dale Watson said. John Lipka, who considers himself a close friend of O'Neill, attributes some of O'Neill's problems to his flamboyant image. "The bureau doesn't like high-profile people," he said. "It's a very conservative culture."

The World Trade Center had become a symbol of America's success in fighting terrorism, and in September, 2000, the New York Joint Terrorism Task Force celebrated its twentieth anniversary in the Windows on the World restaurant. The event was attended by representatives of seventeen law-enforcement agencies, including agents from the F.B.I. and the C.I.A., New York City and Port Authority policemen, United States marshals, and members of the Secret Service. Mary Jo White praised the task force for a "close to absolutely perfect record of successful investigations and convictions." White had served eight years as the United States Attorney for the Southern District, and she had convicted twenty-five Islamic terrorists, including Yousef, six other World Trade Center bombers, the blind cleric Sheikh Omar Abdel Rahman, and nine of Rahman's followers, who had planned to blow up the Lincoln and Holland Tunnels, the United Nations headquarters, and the F.B.I. offices.

O'Neill seemed at ease that night. Few of his colleagues knew of a troubling incident that had occurred two months earlier at an F.B.I. pre-retirement conference in Orlando. During a meeting, O'Neill had been paged. He left the room to return the call, and when he came back, a few minutes later, the other agents had broken for lunch. His briefcase, which contained classified material, was missing. O'Neill immediately called the local police, and they found the briefcase a couple of hours later, in another hotel. A Montblanc pen had been stolen, along with a silver cigar cutter and a lighter. The papers were intact; fingerprint analysis soon established that they had not been touched.

"He phoned me and said, 'I gotta tell you something,' " Barry Mawn recalled. O'Neill told Mawn that the briefcase contained some classified E-mails and one highly sensitive document, the Annual Field Office Report, which is an overview of every counter-terrorist and counter-espionage case in New York. Mawn reported the incident to Neil Gallagher, the bureau's assistant director in charge of national security. "John understood the seriousness of what he had done, and if he were alive today he'd tell you he made a stupid mistake," Gallagher told me. Even though none of the information had been compromised, the Justice Department ordered a criminal inquiry.

Mawn said that, as O'Neill's supervisor, he would have recommended an oral reprimand or, at worst, a letter of censure. Despite their competition for the top job in New York, Mawn had become one of O'Neill's staunchest defenders. "He demanded perfection, which was a large part of why the New York office is so terrific," Mawn said. "But underneath his manner, deep down, he was very insecure."

On October 12, 2000, a small boat filled with C4 explosives motored alongside a U.S. destroyer, the Cole, which was fuelling up off the coast of Yemen. Two men aboard the small craft waved at the larger vessel, then blew themselves to pieces. Seventeen American sailors died, and thirty-nine others were seriously wounded.

O'Neill knew that Yemen was going to be an extremely difficult place in which to conduct an investigation. In 1992, bin Laden's network had bombed a hotel in Aden, hoping to kill a number of American soldiers. The country was filled with spies and with jihadis and was reeling from a 1994 civil war. "Yemen is a country of eighteen million citizens and 50 million machine guns," O'Neill reported. On the day the investigators arrived in Yemen, O'Neill warned them, "This may be the most hostile environment the F.B.I. has ever operated in."

The American Ambassador to Yemen, Barbara Bodine, saw things differently. In her eyes, Yemen was the poor and guileless cousin of the swaggering petro-monarchies of the Persian Gulf. Unlike other countries in the region, it was a constitutional democracy—however fragile—in which women were allowed to vote. Bodine had had extensive experience in Arab countries. During the Iraqi invasion and occupation of Kuwait, she had been the deputy chief of mission in Kuwait City, and she had stayed through the hundred-and-thirty-seven-day siege of the American Embassy by Iraqi troops until all the Americans were evacuated.

Bodine, who is on assignment from the State Department as diplomat-in-residence at the University of California at Santa Barbara, contends that she and O'Neill had agreed that he would bring in a team of no more than fifty. She was furious when three hundred investigators, support staff, and marines arrived, many carrying automatic weapons. "Try to imagine if a military plane from another country landed in Des Moines, and three hundred heavily armed people took over," she told me recently. Bodine recalled that she pleaded with O'Neill to consider the delicate diplomatic environment he was entering. She quoted him as responding, "We don't care about the environment. We're just here to investigate a crime."

"There was the F.B.I. way, and that was it," she said to me. "O'Neill wasn't unique. He was simply extreme." According to Michael Sheehan, who was the State Department's coördinator for counter-terrorism at the time, such conflicts between ambassadors and the bureau are not unusual, given their differing perspectives; however, Bodine had been given clear instructions from the outset of the investigation. "I drafted a cable under [then Secretary of State] Madeleine Albright's signature saying that there were three guiding principles," Sheehan said. "The highest priorities were the immediate safety of American personnel and the investigation of the attack. No. 3 was maintaining a relationship with the government of Yemen— but only to support those objectives."

O'Neill's investigators were billeted three or four to a room in an Aden hotel. "Forty-five F.B.I. personnel slept on mats on the ballroom floor," he later reported. He set up a command post on the eighth floor, which was surrounded by sandbags and protected by a company of fifty marines.

O'Neill spent much of his time coaxing the Yemeni authorities to coöperate. To build a case that would hold up in American courts, he wanted his agents present during interrogations by local authorities, in part to insure that none of the suspects were tortured. He also wanted to gather eyewitness testimony from residents who had seen the explosion. Both the Yemeni authorities and Bodine resisted these requests. "You want a bunch of six-foot-two Irish-Americans to go door-to-door?" Bodine remembers saying to O'Neill. "And, excuse me, but how many of your guys speak Arabic?"

There were only half a dozen Arabic speakers in the F.B.I. contingent, and even O'Neill acknowledged that their competence was sometimes in question. On one occasion, he complained to a Yemeni intelligence officer, "Getting information out of you is like pulling teeth." When his comment was translated, the Yemeni's eyes widened. The translator had told him, "If you don't give me the information I want, I'm going to pull out your teeth."

When O'Neill expressed his frustration to Washington, President Clinton sent a note to President Ali Abdullah Saleh. It had little effect. According to agents on the scene, O'Neill's people were never given the authority they needed for a proper investigation. Much of their time was spent on board the Cole, interviewing sailors, or lounging around the sweltering hotel. Some of O'Neill's requests for evidence mystified the Yemenis. They couldn't understand, for instance, why he was demanding a hat worn by one of the conspirators, which O'Neill wanted to examine for DNA evidence. Even the harbor sludge, which contained residue from the bomb, was off limits until the bureau paid the Yemeni government a million dollars to dredge it.

There were so many perceived threats that the agents often slept in their clothes and with their guns at their sides. Bodine thought that much of this fear was overblown. "They were deeply suspicious of everyone, including the hotel staff," she told me. She assured O'Neill that gunfire outside the hotel was probably not directed at the investigators but was simply the noise of wedding celebrations. Still, she added that, for the investigators' own safety, she wanted to lower the bureau's profile by reducing the number of agents and stripping them of heavy weapons. Upon receiving a bomb threat, the investigators evacuated the hotel and moved to an American vessel, the U.S.S. Duluth. After that, they had to request permission just to come ashore.

Relations between Bodine and O'Neill deteriorated to the point that Barry Mawn flew to Yemen to assess the situation. "She represented that John was insulting, and not getting along well with the Yemenis," he recalled. Mawn talked to members of the F.B.I. team and American military officers, and he observed O'Neill's interactions with Yemeni authorities. He told O'Neill that he was doing "an outstanding job." On Mawn's return, he reported favorably on O'Neill to Freeh, adding that Bodine was his "only detractor."

An ambassador, however, has authority over which Americans are allowed to stay in a foreign country. A month after the investigation began, Assistant Director Dale Watson told the Washington Post, "Sustained cooperation" with the Yemenis "has enabled the F.B.I. to further reduce its in-country presence. . . . The F.B.I. will soon be able to bring home the F.B.I.'s senior on-scene commander, John O'Neill." It appeared to be a very public surrender. The same day, the Yemeni Prime Minister told the Post that no link had been discovered between the Cole bombers and Al Qaeda.

The statement was premature, to say the least. In fact, it is possible that some of the planning for the Cole bombing and the September 11th attacks took place simultaneously. It is now believed that at least two of the suspected conspirators in the Cole bombing had attended a meeting of alleged bin Laden associates in Malaysia, in January, 2000. Under C.I.A. pressure, Malaysian authorities had conducted a surveillance of the gathering, turning up a number of faces but, in the absence of wiretaps, nothing of what was said. "It didn't seem like much at the time," a Clinton Administration official told me. "None of the faces showed up in our own files." Early last year, the F.B.I. targeted the men who were present at the Malaysia meeting as potential terrorists. Two of them were subsequently identified as hijackers in the September 11th attacks.

After two months in Yemen, O'Neill came home feeling that he was fighting the counter-terrorism battle without support from his own government. He had made some progress in gaining access to evidence, but so far the investigation had been a failure. Concerned about continuing threats against the remaining F.B.I. investigators, he tried to return in January of 2001. Bodine denied his application to reënter the country. She refuses to discuss that decision. "Too much is being made of John O'Neill's being in Yemen or not," she told me. "John O'Neill did not discover Al Qaeda. He did not discover Osama bin Laden. So the idea that John or his people or the F.B.I. were somehow barred from doing their job is insulting to the U.S. government, which was working on Al Qaeda before John ever showed up. This is all my embassy did for ten months. The fact that not every single thing John O'Neill asked for was appropriate or possible does not mean that we did not support the investigation."

After O'Neill's departure, the remaining agents, feeling increasingly vulnerable, retreated to the American Embassy in Sanaa, the capital of Yemen. In June, the Yemeni authorities arrested eight men who they said were part of a plot to blow up the Embassy. New threats against the F.B.I. followed, and Freeh, acting upon O'Neill's recommendation, withdrew the team entirely. Its members were, he told me, "the highest target during this period." Bodine calls the pullout "unconscionable." In her opinion, there was never a specific, credible threat against the bureau. The American Embassy, Bodine points out, stayed open. But within days American military forces in the Middle East were put on top alert.

Few people in the bureau knew that O'Neill had a wife and two children (John, Jr., and his younger sister, Carol) in New Jersey, who did not join him when he moved to Chicago, in 1991. In his New York office, the most prominent pictures were not family photographs but French Impressionist prints. On his coffee table was a book about tulips, and his office was always filled with flowers. He was a terrific dancer, and he boasted that he had been on "American Bandstand" when he was a teen-ager. Some women found him irresistibly sexy. Others thought him a cad.

Shortly after he arrived in Chicago, O'Neill met Valerie James, a fashion sales director, who was divorced and was raising two children. Four years later, when he transferred to headquarters, in Washington, he also began seeing Anna DiBattista, who worked for a travel agency. Then, when he moved to New York, Valerie James joined him. In 1999, DiBattista moved to New York to take a new job, complicating his life considerably. His friends in Chicago and New York knew Valerie, and his friends in Washington knew Anna. If his friends happened to see him in the company of the "wrong" woman, he pledged them to secrecy.

On holidays, O'Neill went home to New Jersey to visit his parents and to see his children. Only John P. O'Neill, Jr., who is a computer expert for the credit-card company M.B.N.A., in Wilmington, Delaware, agreed to speak to me about his father. His remarks were guarded. He described a close relationship—"We talked a few times a week"—but there are parts of his father's past that he refuses to discuss. "My father liked to keep his private life private," he said.

Both James and DiBattista remember how O'Neill would beg for forgiveness and then promise better times. James told me, "He'd say, 'I just want to be loved, just love me,' but you couldn't really trust him, so he never got the love he asked for."

The stress of O'Neill's tangled personal life began to affect his professional behavior. One night, he left his Palm Pilot in Yankee Stadium; it was filled with his police contacts all around the world. On another occasion, he left his cell phone in a cab. In the summer of 1999, he and James were driving to the Jersey shore when his Buick broke down near the Meadowlands. As it happened, his bureau car was parked nearby, at a secret office location, and O'Neill switched cars. One of the most frequently violated rules in the bureau is the use of an official vehicle for personal reasons, and O'Neill's infraction might have been overlooked had he not let James enter the building to use the bathroom. "I had no idea what it was," she told me. Still, when the F.B.I. learned about the violation, apparently from an agent who had been caught using the site as an auto-repair shop, O'Neill was reprimanded and docked fifteen days' pay. He regarded the bureau's action as part of a pattern. "The last two years of his life, he got very paranoid," James told me. "He was convinced there were people out to get him."

In March, 2001, Richard Clarke asked the national-security adviser, Condoleezza Rice, for a job change; he wanted to concentrate on computer security. "I was told, 'You've got to recommend somebody similar to be your replacement,' " Clarke recalled. "I said, 'Well, there's only one person who would fit that bill.' " For months, Clarke tried to persuade O'Neill to become a candidate as his successor.

O'Neill had always harbored two aspirations—to become a deputy director of the bureau in Washington or to take over the New York office. Freeh was retiring in June, so there were likely to be some vacancies at the top, but the investigation into the briefcase incident would likely block any promotion in the bureau. O'Neill viewed Clarke's job as, in many ways, a perfect fit for him. But he was financially pressed, and Clarke's job paid no more than he was making at the F.B.I. Throughout the summer, O'Neill refused to commit himself to Clarke's offer. He talked about it with a number of friends but became alarmed when he thought that headquarters might hear of it. "He called me in a worked-up state," Clarke recalled. "He said that people in the C.I.A. and elsewhere know you are considering recommending me for your job. You have to tell them it's not true." Clarke dutifully called a friend in the agency, even though O'Neill still wanted to be a candidate for the position.

In July, O'Neill heard of a job opening in the private sector which would pay more than twice his government salary—that of chief of security for the World Trade Center. Although the Justice Department dropped its inquiry into the briefcase incident, the bureau was conducting an internal investigation of its own. O'Neill was aware that the Times was preparing a story about the affair, and he learned that the reporters also knew about the incident in New Jersey involving James and had classified information that probably came from the bureau's investigative files.The leak seemed to be timed to destroy O'Neill's chance of being confirmed for the N.S.C. job. He decided to retire.

O'Neill suspected that the source of the information was either Tom Pickard or Dale Watson. The antagonism between him and Pickard was well known. "I've got a pretty good Irish temper and so did John," Pickard, who retired last November, told me. But he insisted that their differences were professional, not personal. The leak was "somebody being pretty vicious to John," but Pickard maintained that he did not do it. "I'd take a polygraph to it," he said. Watson told me, "If you're asking me who leaks F.B.I. information, I have no idea. I know I don't, and I know that Tom Pickard doesn't, and I know that the director doesn't." For all the talk about polygraphs, the bureau ruled out an investigation into the source of the leak, despite an official request by Barry Mawn, in New York.

Meanwhile, intelligence had been streaming in concerning a likely Al Qaeda attack. "It all came together in the third week in June," Clarke said. "The C.I.A.'s view was that a major terrorist attack was coming in the next several weeks." On July 5th, Clarke summoned all the domestic security agencies—the Federal Aviation Administration, the Coast Guard, Customs, the Immigration and Naturalization Service, and the F.B.I.—and told them to increase their security in light of an impending attack.

On August 19th, the Times ran an article about the briefcase incident and O'Neill's forthcoming retirement, which was to take place three days later. There was a little gathering for coffee as he packed up his office.

When O'Neill told ABC's Isham of his decision to work at the Trade Center, Isham had said jokingly, "At least they're not going to bomb it again." O'Neill had replied, "They'll probably try to finish the job." On the day he started at the Trade Center—August 23rd—the C.I.A. sent a cable to the F.B.I. saying that two suspected Al Qaeda terrorists were already in the country. The bureau tried to track them down, but the addresses they had given when they entered the country proved to be false, and the men were never located.

When he was growing up in Atlantic City, O'Neill was an altar boy at St. Nicholas of Tolentine Church. On September 28th, a week after his body was found in the rubble of the World Trade Center, a thousand mourners gathered at St. Nicholas to say farewell. Many of them were agents and policemen and members of foreign intelligence services who had followed O'Neill into the war against terrorism long before it became a rallying cry for the nation. The hierarchy of the F.B.I. attended, including the now retired director Louis Freeh. Richard Clarke, who says that he had not shed a tear since September 11th, suddenly broke down when the bagpipes played and the casket passed by.

O'Neill's last weeks had been happy ones. The moment he left the F.B.I., his spirits had lifted. He talked about getting a new Mercedes to replace his old Buick. He told Anna that they could now afford to get married. On the last Saturday night of his life, he attended a wedding with Valerie, and they danced nearly every number. He told a friend within Valerie's hearing, "I'm gonna get her a ring."

On September 10th, O'Neill called Robert Tucker, a friend and security-company executive, and arranged to get together that evening to talk about security issues at the Trade Center. Tucker met O'Neill in the lobby of the north tower, and the two men rode the elevator up to O'Neill's new office, on the thirty-fourth floor. "He was incredibly proud of what he was doing," Tucker told me. Then they went to a bar at the top of the tower for a drink. Afterward, they headed uptown to Elaine's, where they were joined by their friend Jerry Hauer. Around midnight, the three men dropped in on the China Club, a night spot in midtown. "John made the statement that he thought something big was going to happen," Hauer recalled.

Valerie James waited up for O'Neill. He didn't come in until 2:30 A.M. "The next morning, I was frosty," she recalled. "He came into my bathroom and put his arms around me. He said, 'Please forgive me.' " He offered to drive her to work, and dropped her off at eight-thirteen in the flower district, where she had an appointment, and headed to the Trade Center.

At 8:46 A.M., when American Airlines Flight 11 crashed into the north tower, John P. O'Neill, Jr., was on a train to New York, to install some computer equipment and visit his father's new office. From the window of the train he saw smoke coming from the Trade Center. He called his father on his cell phone. "He said he was O.K. He was on his way out to assess the damage," John, Jr., recalled.

Valerie James was arranging flowers in her office when "the phones started ringing off the hook." A second airliner had just hit the south tower. "At nine-seventeen, John calls," James remembered. He said, "Honey, I want you to know I'm O.K. My God, Val, it's terrible. There are body parts everywhere. Are you crying?" he asked. She was. Then he said, "Val, I think my employers are dead. I can't lose this job."

"They're going to need you more than ever," she told him.

At nine-twenty-five, Anna DiBattista, who was driving to Philadelphia on business, received a call from O'Neill. "The connection was good at the beginning," she recalled. "He was safe and outside. He said he was O.K. I said, 'Are you sure you're out of the building?' He told me he loved me. I knew he was going to go back in."

Wesley Wong, an F.B.I. agent who had known O'Neill for more than twenty years, raced over to the north tower to help set up a command center. "John arrived on the scene," Wong recalled. "He asked me if there was any information I could divulge. I knew he was now basically an outsider. One of the questions he asked was 'Is it true the Pentagon has been hit?' I said, 'Gee, John, I don't know. Let me try to find out.' At one point, he was on his cell phone and he was having trouble with the reception and started walking away. I said, 'I'll catch up with you later.' "

Wong last saw O'Neill walking toward the tunnel leading to the second tower.