Before Sunday (May 1), the last time an American President thought he had Osama bin Laden in his sights was the late summer of 2007.

Al-Qaeda and Taliban commanders, terrorist volunteers and insurgent foot soldiers would be meeting in the Tora Bora region of Afghanistan, a stream of intelligence reports showed. And there were hints that bin Laden himself might travel from his hiding place in Pakistan to rally militants training for large-scale suicide attacks in Europe or the United States.

“We thought we had ‘No. 1' on this side of the border,” said a senior American military officer involved in planning the operation. “It was the best intelligence we'd had on him in a long time.”

The military set into motion one of the largest strike missions of its kind, with long-range bombers, attack helicopters, artillery and commandos all ready to pummel the rugged mountain valley along Afghanistan's border with Pakistan, according to military officers and former government officials.

But just as the half dozen B-2 Stealth bombers were halfway on the 3,000-mile flight to their target, commanders ordered them to return to their secret base in the Indian Ocean, because of doubts about the intelligence on Bin Laden and concerns about civilian casualties from the bombs.

A smaller, more precise raid was carried out by commandos and attack helicopters, killing several dozen militants in the episode, which has not been previously disclosed.

But the founder and formative figure of al-Qaeda was not there.

Inside the White House, the disappointment was palpable, according to senior aides to former President George W. Bush. What might have been Mr. Bush's last chance at redeeming his administration's failure to capture or kill Bin Laden after the 2001 invasion of Afghanistan, when he was cornered in the same Tora Bora region but escaped into Pakistan, did not materialise.

Amid the national relief over the killing of bin Laden by a Navy Seal team in Abbottabad, Pakistan, this secret chapter in the hunt for the world's most famous fugitive is a reminder of the years of frustration and false hopes government officials endured in trying to pick up his trail.

Lessons of the 2007 mission

Lessons of the 2007 mission echoed through the White House and the Pentagon in recent months, as a fresh stream of intelligence pointed to a compound in Abbottabad that appeared to house bin Laden. The options presented to President Barack Obama for the raid that killed bin Laden were strikingly similar to those drawn up in 2007, as tensions in Washington heated up over reports of possible terrorist plots emanating from Pakistan.

At that time, Afghan intelligence officers, eavesdropping on insurgent conversations in the early summer of 2007, first picked up strong indications that Taliban and Qaeda fighters were planning the largest gathering in Afghanistan since early in the war. The intelligence was so compelling that President Hamid Karzai of Afghanistan summoned American officers to his palace in Kabul to request a major American operation to crush the fighters.

It was not just the Afghans who were tracking bin Laden's potential movements. Independently, the American Special Operations unit assigned to hunt high-level Qaeda and Taliban leaders in Afghanistan, with analysts from the Central Intelligence Agency and other American spy organisations working alongside, had gathered information that more than 100 Taliban and Qaeda commanders and fighters planned to enter Afghanistan from Pakistan through Tora Bora.

Part of a new book

This intelligence stream suggesting a bin Laden plan to slip into Tora Bora, and the attack devised to kill him in 2007, was uncovered in reporting about the episode conducted for a book, “Counterstrike: The Untold Story of America's Secret Campaign Against Al Qaeda.” It will be published in August by Times Books, an imprint of Henry Holt and Company.

The account of the 2007 attack is based on interviews with almost a dozen military officers and former Bush administration officials, speaking only on the condition of anonymity, who were involved in planning the mission. On Thursday (May 5), Bryan Whitman, a Pentagon spokesman, declined to comment about the episode, saying the Defence Department did not discuss, or even confirm, such classified missions.

The rugged, rocky region of Tora Bora is honeycombed with caves, some of which were used by the mujahedeen in their standoff against the Soviet Army in the 1980s. The terrain, easy to defend and hard to attack, had been the site of bin Laden's last stand before he escaped into Pakistan in the winter of 2001-2002, a missed chance that was a blow to the Bush administration.

Faint if tantalising hints that bin Laden was going to join the insurgent and terrorist gathering, a meeting described by military officers as akin to a congress of Mafia dons, seized the attention of senior administration officials. The intelligence reports were viewed as solid enough that they were briefed all the way up to Mr. Bush, former White House aides said.

Because Afghanistan was a declared war zone, the regional military commander had authority to carry out the raid without requiring Mr. Bush's approval in advance, officials said.

Top military and intelligence officers who read the reports said the camps in Tora Bora were used not merely as a staging area for attacks across Afghanistan but as a planning and training area for an intended high-visibility, mass-casualty attack somewhere outside Afghanistan, in Western Europe or perhaps even the United States.

That larger threat is what led some to interpret the intelligence as indicating Bin Laden himself might be in attendance — to motivate suicide bombers and bless a mission that would perhaps try to replicate the scale of the September 11, 2001, attacks.

“The threat stream was viable,” said one senior military officer. “The area was a hub for high-value leaders, midlevel commanders and foot soldiers. It was a command-and-control centre. They went there as a launching pad to fight inside Afghanistan, but also to plan and train for a spectacular attack outside the theatre of combat.”

As often happens in the uncertain world of intelligence, there were divisions among analysts over whether bin Laden would show up. “If UBL had been there, it would have been just luck,” scoffed one commander, using the government's initials for al-Qaeda's founder.

Others who thought it more likely that bin Laden might address the militants argued that Tora Bora was one of the few areas of Afghanistan in which he might feel safe moving.

Even as the analysts argued over the intelligence in 2007, Special Operations planners were taking no chances. If this terrorist war council did convene, and bin Laden might be there, he would not escape Tora Bora again, they vowed.

One of the largest missions

Planners, over a period of weeks, began building one of the largest missions of its kind.

In addition to assigning about half a dozen B-2 bombers to the mission, dozens of attack jets were in place, ready to strike with precision-guided bombs. On the ground, the military deployed a new, long-range artillery system. Helicopter gunships and Special Operations troops were in place to go in to kill or capture any insurgents who escaped the initial aerial bombardment.

“It was going to be a piling on,” said one senior American officer. The size of the mission, coupled with the ambiguity of the intelligence, alarmed some senior United States commanders, including Adm. William J. Fallon, then the head of Central Command.

“Fallon's view was you're swatting a fly with a 16-pound hammer,” said the senior American officer, who was familiar with the commander's thinking.

Diplomatic and political concerns also surfaced. The B-2s would be flying from a British air base in Diego Garcia, a tiny island in the Indian Ocean, and would need to fly through Pakistani airspace to carry out the mission. While the bombs aboard each B-2 were satellite-guided, there was a risk that one could fall into Pakistan territory.

In late July, as the date of the militants' meeting approached, civilian and military analysts pored over intelligence reports and communications intercepts for fresh clues. The picture was still murky. Even so, commanders were given the green light a few days later and ordered the B-2s to take off, to be in position if the meeting materialised.

But roughly halfway to their targets, Admiral Fallon called them off. “This was carpet bombing, pure and simple,” said another top military officer who had openly voiced disagreement with the operation. “It was not precision-targeted. There was no way to separate the al-Qaeda leadership that might be on hand, and the fighters, from the local population and the camp followers.”

More than three years later, Mr. Obama was presented with a near carbon copy of such a bombing option as he considered how to attack a compound in Abbottabad believed to be bin Laden's refuge.

But the President and his war council decided that it was important to be able to prove that they had, in fact, killed or captured bin Laden. Rather than obliterating the three-story house and everyone inside, they rejected a large bombing attack and approved the riskier commando raid that killed him.

To this day, senior military and intelligence officials debate whether bin Laden had decided not to travel to the meeting in Tora Bora in 2007 because the risk was too high, whether the American operation was tipped off to al-Qaeda or Taliban operatives through Afghan or Pakistani sources — or whether the intelligence had been interpreted incorrectly from the outset.

“What we thought was happening didn't happen,” said one former senior administration official. “And nobody knows why.” — New York Times News Service

More In: Comment | Opinion