Erik de Castro/Reuters/Corbis

Dec. 16, 2001 Despite the Afghan and American assault on Tora Bora, Osama bin Laden escaped.

well past midnight one morning in early December 2001, according to American intelligence officials, Osama bin Laden sat with a group of top aides - including members of his elite international 055 Brigade - in the mountainous redoubt of Tora Bora in eastern Afghanistan. Outside, it was blustery and bitterly cold; many of the passes of the White Mountains, of which Tora Bora forms a part, were already blocked by snow. But inside the cave complex, where bin Laden had sought his final refuge from the American war in Afghanistan - a war in which Washington, that October, had struck back for the Sept. 11 terrorist attacks - bin Laden munched on olives and sipped sugary mint tea. He was dressed in his signature camouflage jacket, and a Kalashnikov rested by his side. Captured Qaeda fighters, interviewed separately, told American interrogators that they recalled an address that bin Laden had made to his followers shortly before dawn. It concerned martyrdom. American bombs, including a 15,000-pound "daisy cutter," were raining from the sky and pulverizing a number of the Tora Bora caves. And yet, one American intelligence official told me recently, if any one thing distinguished Osama bin Laden on that cold December day, it was the fact that the 44-year-old Saudi multimillionaire appeared to be supremely confident.

The first time bin Laden had seen the Tora Bora caves, he had been a young mujahedeen fighter and a recent university graduate with a degree in civil engineering. It had been some 20 years before, during Washington's first Afghan war, the decade-long, C.I.A.-financed jihad of the 1980's against the Soviet occupation. Rising to more than 13,000 feet, 35 miles southwest of the provincial capital of Jalalabad, Tora Bora was a fortress of snow-capped peaks, steep valleys and fortified caves. Its miles of tunnels, bunkers and base camps, dug deeply into the steep rock walls, had been part of a C.I.A.-financed complex built for the mujahedeen. Bin Laden had flown in dozens of bulldozers and other pieces of heavy equipment from his father's construction empire, the Saudi Binladin Group, one of the most prosperous construction companies in Saudi Arabia and throughout the Persian Gulf. According to one frequently told story, bin Laden would drive one of the bulldozers himself across the precipitous mountain peaks, constructing defensive tunnels and storage depots. Indeed, by December 2001, when the final battle of Tora Bora took place, the cave complex had been so refined that it was said to have its own ventilation system and a power system created by a series of hydroelectric generators; bin Laden is believed to have designed the latter. Tora Bora's walls and the floors of its hundreds of rooms were finished and smooth and extended some 350 yards into the granite mountain that enveloped them. Now, as the last major battle of the war in Afghanistan began, hidden from view inside the caves were an estimated 1,500 to 2,000 well-trained, well-armed men. A mile below, at the base of the caves, some three dozen U.S. Special Forces troops fanned out. They were the only ground forces that senior American military leaders had committed to the Tora Bora campaign.

Yunis Khalis long worried that such a moment would arrive. A theologian and warrior of considerable repute, Khalis knew the Americans well: he had fought for them two decades before. And if there was one thing that the octogenarian leader knew, it was that he really didn't like the Americans much at all. Nevertheless, as one head of the fratricidal alliance of Afghan resistance groups, he had accepted Washington's largess, and over the years, as the war against the Soviet occupiers progressed, Khalis, among the seven resistance leaders, would receive the third-largest share of the more than $3 billion of weapons and funds that the C.I.A. invested in the jihad. As the godfather of Jalalabad, the capital of the province of Nangarhar, Khalis controlled a vast territory, including Tora Bora. It had been a key operational center for his fighters during the anti-Soviet war. And it was a key operational center for Osama bin Laden now. The caves were so close that Khalis could see them from the verandah of his sprawling stucco home.

One evening earlier this summer, I asked Masood Farivar, a former Khalis officer who had fought in Tora Bora during the jihad, to tell me why the caves were so important. "They're rugged, formidable and isolated," he said. "If you know them, you can come and go with ease. But if you don't, they're a labyrinth that you can't penetrate. They rise in some places to 14,000 feet, and for 10 years the Soviets pummeled them with everything they had, but to absolutely no avail. Another reason they're so important is their proximity to the border and to Pakistan" - less than 20 miles away.

Bin Laden knew the caves as well as Farivar and Khalis did. He had fought in nearby Jaji and Ali Khel and in the 1989 battle of Jalalabad. He knew every ridge and mountain pass, every C.I.A. trail. For this was the area where bin Laden had spent more than a decade of his life.

It was also during the war years that bin Laden first met Khalis; the two men became very close friends. Indeed, when bin Laden returned to Afghanistan in May 1996 from his base in the Sudan (after the United States insisted that the Sudanese government expel him), it was Khalis, along with two of his key commanders - Hajji Abdul Qadir and Engineer Mahmoud - who first invited him. And it was also Khalis who, later that year, would introduce bin Laden to the one-eyed leader of the Taliban, Mullah Muhammad Omar, who had fought with Khalis - and would later become his protégé - during the jihad.

"Khalis had an avuncular interest in bin Laden," Michael Scheuer, the former head of the C.I.A.'s bin Laden unit and the author of "Imperial Hubris," told me recently when we met at a Washington coffeehouse. "Osama lost his father when he was young, and Khalis became a substitute father figure to him. As far as Khalis was concerned, he considered Osama the perfect Islamic youth."

Bin Laden, along with his four wives and 20-some children, moved into the well-fortified Khalis family compound nine years ago and then to a farm on the outskirts of Jalalabad. But shortly thereafter, Engineer Mahmoud was assassinated, and there were two assassination attempts against bin Laden, too. "They were both very crude," Scheuer said, "and they smacked of the Saudis" - who had earlier tried to assassinate bin Laden in Khartoum. "As a result, bin Laden wanted to move away from the main road. So Khalis gave him two of his fighting positions in the mountains - Tora Bora and Milawa. Bin Laden immediately began to customize and rebuild the two: Tora Bora for his family and his key aides; Milawa for his fighters and as a command center and logistics hub. By the time bin Laden moved to Kandahar" - then a Taliban stronghold - "in May of 1997, the two mountain redoubts had been completely refurbished and modernized: they were there, just waiting for him in 2001."

Some six weeks after the Sept. 11 attacks and nearly two weeks after the bombing of Afghanistan began on Oct. 7, American military leaders - who had no off-the-shelf invasion plans, not even an outline, for Afghanistan - finally succeeded in getting the first forces in: a 12-man Special Forces A-team helicoptered in from Uzbekistan to the Panjshir Valley. There they joined forces with the Northern Alliance, an anti-Taliban militia that controlled only 10 percent of Afghanistan but to whom Washington delegated the ground war. The view prevailing among senior American military leaders was that overwhelming air power, suitcases full of cash and surrogate militias could win the war. The intricacies of Afghan tribal life appeared to elude everyone.

In late October or early November, according to Scheuer, American operatives went to see Khalis to seek his support. "Khalis said that he was retired and doing nothing now," Scheuer told me. "It was the last time" American intelligence officials saw him. "It was so bizarre! Didn't anybody know about Khalis's friendship with bin Laden? Or that Khalis was the only one of the seven mujahedeen leaders who remained neutral about, and sometimes even supported, the Taliban?" He shook his head and then went on: "And even after Sept. 11, indeed in spite of it, as soon as our bombing of Afghanistan began, Khalis issued a well-publicized call for jihad against U.S. forces in Afghanistan."

When Khalis turned the Americans down, Special Forces troops recruited two of his former commanders. They made an unlikely couple: Hazarat Ali and Hajji Zaman. The former, with just a fourth-grade education, was barely literate, a bully and unrefined; the other was a wealthy drug smuggler, fluent in English and French, and a polished raconteur who was lured back to Afghanistan from his exile in France by the United States. Both were schemers who had come of age on the battlefields of the anti-Soviet war, Ali as a teenager in Tora Bora and Zaman in Jalalabad. Ali had joined the Taliban for a time, then moved north and embraced the Northern Alliance; Zaman had supported neither, and when the Taliban came to power, he chose exile. Ali owed his rise largely to the Pentagon, which ultimately enlisted him to lead the ground battle in the Tora Bora caves; Zaman, a Pashtun leader and member of the Khugyani Tribe, had his own base of support, something that Ali, a member of a minor, non-Pashtun tribal grouping, lacked.

A third militia leader - less experienced but of more distinguished pedigree - who would bring his forces to Tora Bora was Hajji Zahir, the 27-year-old somewhat skittish son of Hajji Abdul Qadir, Yunis Khalis's former military commander and one of the three men who had welcomed bin Laden when he returned to Afghanistan. Indeed, as the Americans were recruiting his son, Hajji Abdul Qadir was about to reclaim the governorship of Nangarhar Province, a post he had relinquished when the Taliban arrived, in a power transfer Khalis and bin Laden would help to consummate.

Bin Laden had returned to Jalalabad on or about Nov. 10, a U.S. intelligence official told me recently, and that same afternoon, according to a March 4, 2002, report in The Christian Science Monitor, he gave a fiery speech at the Jalalabad Islamic studies center - as American bombs exploded nearby - to a thousand or so regional tribal leaders, vowing that if united they could teach the Americans "a lesson, the same one we taught the Russians" when many of the chieftains had fought in America's first Afghan war. Dressed in a gray shalwar kameez, the long shirt and bloused trousers favored in Afghanistan, and his camouflage jacket, bin Laden held a small Kalakov, a shorter version of the Kalashnikov, in his hand. As the crowd began to shout "Zindibad [Long live] Osama," the leader of Al Qaeda moved through the banquet hall dispensing white envelopes, some bulky, some thin, the thickness proportionate to the number of extended families under each leader's command. Lesser chieftains, according to those present, received the equivalent of $300 in Pakistani rupees; leaders of larger clans, up to $10,000.

Bin Laden really didn't have to buy the loyalty of the Pashtun tribal chiefs; they were already devoted to him. He was, after all, the only non-Afghan Muslim of any consequence in the past half-century who had stood with the Afghans. But on that November afternoon, and on the nights that followed it, as bin Laden began to lay the groundwork for his escape from the Tora Bora caves, the elusive Qaeda leader was determined to be absolutely sure.

The following evening, or the evening after, bin Laden, according to an Afghan intelligence official, dined in Jalalabad with other Pashtun tribal chiefs from Parachinar, Pakistan, an old military outpost I first visited nearly 20 years before. Parachinar had been a key staging area for the C.I.A. during the jihad, and its tribal leaders had profited immensely. A picturesque town in the Kurram Valley, Parachinar was also Pakistan's first line of defense against any Afghan incursion. Beyond it lie only the White Mountains - and the caves of Tora Bora - and desolate stretches of no man's land.

The last time bin Laden was seen in Jalalabad was the evening of Nov. 13, when he, along with Khalis's son, Mujahid Ullah, and other tribal leaders negotiated a peaceful hand-over of power from the Taliban to a caretaker government. Under its terms, Khalis would take temporary control of the city until the formation of a newly appointed U.S.-backed government. He, of course, made certain that the Eastern Shura, as the government is called, was stacked with men who owed their loyalty to him. Hajji Abdul Qadir, his former military commander, became Nangarhar Province's governor again.

Bin Laden's Arab fighters had used Jalalabad as a base and as a command center for a number of years, and now they dispersed, loading their weapons and their clothing, their children and their wives into the backs of several hundred lorries, armored vehicles and four-wheel-drive trucks. Some Taliban fighters followed suit. Others disappeared, removing their signature black turbans and returning to their villages and towns.

As the convoy was being readied, bin Laden said his goodbyes: to the Taliban governor; to Mujahid Ullah, Khalis's son; and to scores of the tribal leaders who had received his white envelopes three days before. He was dressed now as he had been dressed then and cradled his Kalakov, even though he was surrounded by some 60 armed guards.

Then he entered a custom-designed white Toyota Corolla, and the convoy sped away toward the mountains of Tora Bora, where he waited for the Americans to arrive.

By late November, Hazarat Ali, Hajji Zaman and Hajji Zahir had assembled a motley force of some 2,500 men - supplemented by a fleet of battered Russian tanks - at the base of Tora Bora. The Afghans were ill equipped and poorly trained. They also lacked the commitment that bin Laden's fighters had. Hidden from view at 5,000 feet and above in the scores of valleys, forests and caves, the Qaeda fighters not only had the tremendous advantage of the terrain; their redoubts were replete with generators, electricity and heat and copious stocks of provisions. Snow covered the mountain, and it was bitterly cold. The Afghan fighters at its base grumbled and quarreled endlessly. It was also the holy month of Ramadan, when Muslims fast from dawn to dusk, and some of the Afghans had the irritating tendency to leave their posts and return home to celebrate iftar, the evening meal that breaks the fast.

Perhaps more ominous was the growing antipathy between Hazarat Ali and Hajji Zaman: both ruthless, both greedy, both corrupt, both flashing fistfuls of new $100 bills - one a Pashtun, the other not. Their mutual loathing became so intense that on more than one occasion they and their fighters, instead of fighting Al Qaeda, shot each other's men.

The American bombardment of Tora Bora, which had been going on for a month, yielded to saturation airstrikes on Nov. 30 in anticipation of the ground war. Hundreds of civilians died that weekend, along with a number of Afghan fighters, according to Hajji Zaman, who had already dispatched tribal elders from the region to plead with bin Laden's commanders to abandon Tora Bora. Three days later, on Dec. 3, in one of the war's more shambolic moments, Hazarat Ali announced that the ground offensive would begin. Word quickly spread through the villages and towns, and hundreds of ill-prepared men rushed to the mountain's base. The timing of the call to war was so unexpected that Hajji Zahir, one of its three lead commanders, told journalists at the time that he nearly slept through it.

On a map, it was little more than a mile from the bottom of the White Mountains to the first tier of the Qaeda caves, but the snow was thick and the slopes were steep and, for the Afghan fighters, it was a three-hour climb. They were ambushed nearly as soon as they arrived. The battle lasted for only 10 minutes before bin Laden's fighters disappeared up the slope and the Afghans limped away. Over the coming days, a pattern would emerge: the Afghans would strike, then retreat. On some occasions, a cave would change hands twice in one day. It was only on the third day of the battle that the three dozen Special Forces troops arrived. But their mission was strictly limited to assisting and advising and calling in air strikes, according to the orders of Gen. Tommy Franks, the head of U.S. Central Command, who was running the war from his headquarters in Tampa, Fla.

Even after the arrival of the Special Forces, the Afghan militias were making little headway in their efforts to assault the Qaeda caves - largely as a result of heavier resistance than they had expected - despite having launched simultaneous attacks from the east, west and north. They had sent none of their forces to the south, where the highest peaks of the White Mountains are bisected by the border with Pakistan. The commanders, according to news reports, argued vehemently among themselves on what the conditions on the southern side of the mountain were: some insisted it was uncrossable, closed in by snow; other commanders were far less sure.

By now, the Taliban's stronghold in Kandahar had fallen or, more correctly, had been abandoned by the soldiers of the regime. The Taliban retreat from Kandahar was emblematic of the war. None of Afghanistan's cities had been won by force alone. Taliban fighters, after intense bombing, had simply made strategic withdrawals. A number of American officers were now convinced that this was about to happen at Tora Bora, too.

One of them was Brig. Gen. James N. Mattis, the commander of some 4,000 marines who had arrived in the Afghan theater by now. Mattis, along with another officer with whom I spoke, was convinced that with these numbers he could have surrounded and sealed off bin Laden's lair, as well as deployed troops to the most sensitive portions of the largely unpatrolled border with Pakistan. He argued strongly that he should be permitted to proceed to the Tora Bora caves. The general was turned down. An American intelligence official told me that the Bush administration later concluded that the refusal of Centcom to dispatch the marines - along with their failure to commit U.S. ground forces to Afghanistan generally - was the gravest error of the war.

A week or so after General Mattis's request was denied, the turning point in the battle of Tora Bora came. It was Dec. 12. Hajji Zaman had by now realized that the Qaeda fighters were better armed than his men and that they were also prepared to die rather than surrender to him. He was also becoming increasingly irritated with Hazarat Ali and with the snow. And in a few days the feast of Eid al-Fitr, which ends Ramadan, would begin. The stalemate, the Americans' surrogate commander decided, simply had to end. So, through a series of intermediaries and then directly, Hajji Zaman made radio contact with some of bin Laden's commanders and offered a cease-fire. The Americans were furious. The negotiations - to which Hazarat Ali acquiesced since he, too, was now holding secret talks with Al Qaeda - continued for hours. By the time they came to an end, Hajji Zaman's interlocutor, hidden somewhere in the caves above, was probably bin Laden's son Salah Uddin. If the Qaeda forces surrendered, Hajji Zaman's contact said, it would be only to the United Nations. Then he requested additional time to meet with other commanders. He would be back in touch by 8 the following morning, the younger bin Laden said.

American intelligence officials now believe that some 800 Qaeda fighters escaped Tora Bora that night. Others had already left; still others stayed behind, including bin Laden. "You've got to give him credit," Gary Schroen, a former C.I.A. officer who led the first American paramilitary team into Afghanistan in 2001, told me. "He stayed in Tora Bora until the bitter end." By the time the Afghan militias advanced to the last of the Tora Bora caves, no one of any significance remained: about 20 bedraggled young men were taken prisoner that day, Dec. 17.

On or about Dec. 16, 2001, according to American intelligence estimates, bin Laden left Tora Bora for the last time, accompanied by bodyguards and aides. Other Qaeda leaders dispersed by different routes, but bin Laden and his men are believed to have journeyed on horseback directly south toward Pakistan, crossing through the same mountain passes and over the same little-known smugglers' trails through which the C.I.A.'s convoys passed during the jihad years. And all along the route, in the dozens of villages and towns on both sides of the frontier, the Pashtun tribes would have lighted campfires along the way to guide the horsemen as they slowly continued through the snow and on toward the old Pakistani military outpost of Parachinar.

Tora Bora was the one time after the 9/11 attacks when United States operatives were confident they knew precisely where Osama bin Laden was and could have captured or killed him. Some have argued that it was Washington's last chance; others say that although it will be considerably more difficult now, bin Laden is not beyond our reach. But the stakes are considerably higher than they were nearly four years ago, and terrain and political sensibilities are far more our natural enemies now.

There is no indication that bin Laden ever left Pakistan after he crossed the border that snowy December night; nor is there any indication that he ever left the country's Pashtun tribal lands, moving from Parachinar to Waziristan, then north into Mohmand and Bajaur, one American intelligence official told me. The areas are among the most remote and rugged on earth, and they are vast. Had bin Laden been surrounded at Tora Bora, he would have been confined to an area of several dozen square miles; now he could well be in an area that snakes across some 40,000 square miles.

Defending its decision not to commit forces to the Tora Bora campaign, members of the Bush administration - including the president, the vice president and Gen. Tommy Franks - have continued to insist, as recently as the last presidential campaign, that there was no definitive information that bin Laden was even in Tora Bora in December 2001. "We don't know to this day whether Mr. bin Laden was at Tora Bora," Franks wrote in an Oct. 19, 2004, Op-Ed article in The New York Times. Intelligence assessments on the Qaeda leader's location varied, Franks continued, and bin Laden was "never within our grasp." It was not until this spring that the Pentagon, after a Freedom of Information Act request, released a document to The Associated Press that says Pentagon investigators believed that bin Laden was at Tora Bora and that he escaped.

The document's release came at a particularly delicate time for the United States. A newly resurgent Taliban was on the rise. Its attacks on American forces - launched from Pakistan, according to Afghan officials - were more lethal, better organized and more widespread than at any time since the war against terror began. And President Pervez Musharraf, the military ruler of Pakistan who is ostensibly our key ally in that war, had, to a growing extent, become an ally on his own terms. It was only in the last days of July that he once again committed himself to embark on a campaign against his country's Islamic militants. And this was only as a result of suggestions that there were Pakistani links to the bombings that month in London and the Egyptian resort of Sharm el-Sheikh.

At the same time, to Musharraf's irritation, reports surfaced again - from Indian and Afghan officials, Taliban prisoners and opposition politicians in Pakistan - of terrorist training camps in the Mansehra district of northern Pakistan and the restive southern province of Baluchistan. There, the provincial capital of Quetta had, for all intents and purposes, become a Taliban town. Black-turbaned Talibs swaggered through its bazaars, photographs of bin Laden and Taliban banners adorned its muddy lanes and the Taliban leader Mullah Omar was believed to be in residence.

I puzzled over whether Musharraf's new determination would include finally becoming serious about the hunt for bin Laden. No one to whom I spoke was at all convinced. A few weeks earlier, I had asked George Perkovich of the Carnegie Endowment for International Peace, an expert on South Asian security issues, what he thought about Musharraf's commitment to the search generally. "For me, the outstanding question is, At the highest levels in Islamabad is there a conviction that capturing or killing bin Laden would be good for the leadership of Pakistan?" Perkovich replied. "And given the answer to that question, how hard are they willing to try? And can they afford to be seen as being solidly on America's side? I think Musharraf also worries about whether or not Washington will stay the course. Therefore, he's got to keep the Americans online: hold back something that they want. And, in that respect, Osama could be seen as an insurance policy for them." According to Gary Schroen, the former C.I.A. officer, "We're never going to get bin Laden without the total cooperation of Pakistan, and there's a lot more they could do." "Such as?" I asked. "Winning over their military is imperative," he said. "We've got to convince them that it's in their interest to bring bin Laden in. And that means allowing us to send Special Forces and C.I.A. teams, in sufficient numbers, into the northern areas with the ability to move around, to establish networks on the ground. We've also got to refocus U.S. military strategy in Afghanistan in order to have coordinated military operations between the two sides of the frontier." He paused and said, "It's all up to the Pakistanis now."

"How would this affect Musharraf if he agreed?" I asked.

He thought for a moment, and then he replied, "If his hand was ever seen as the one that turned bin Laden over, he wouldn't be able to survive."

Mary Anne Weaver, who has been a Guggenheim fellow and a Council on Foreign Relations fellow this year, is the author of "Pakistan: In the Shadow of Jihad and Afghanistan."

Copyright 2005 The New York Times Company. Reprinted from The New York Times magazine of Sunday, September 11, 2005.

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