After years of dead ends and promising leads gone cold, the big break came last August.
A trusted courier of Osama bin Laden's whom American spies had been hunting for years was finally located in a compound 35 miles north of the Pakistani capital. The property was so secure, so large, that American officials guessed it was built to hide someone far more important than a mere courier.
What followed was eight months of painstaking intelligence work, culminating in a helicopter assault by American military and intelligence operatives that ended in bin Laden's death on Sunday and concluded one of history's most extensive and frustrating manhunts.
For nearly a decade, American military and intelligence forces had chased the specter of bin Laden through Pakistan and Afghanistan, once coming agonizingly close and losing him in a pitched battle at Tora Bora, in the mountains of eastern Afghanistan in December 2001. As Obama administration officials described it, the real breakthrough came when they finally figured out the name and location of bin Laden's most trusted courier, whom the Al Qaeda chief appeared to rely on to maintain contacts with the outside world.
Detainees at the prison at Guantánamo Bay, Cuba, had given the courier's pseudonym to American interrogators and said that the man was a protégé of Khalid Shaikh Mohammed, the confessed mastermind of the Sept. 11 attacks.
U.S. intelligence officials say they finally learned the courier's real name four years ago, but that it took another two years for them to learn the general region where he operated. And it was not until August that they tracked him to the compound in Abbottabad, a medium-sized city about an hour's drive north of Islamabad, the capital of Pakistan.
C.I.A. analysts spent the next several weeks examining satellite photos and intelligence reports to determine who might be living at the compound. By September, the C.I.A. had decided that there was a "strong possibility" that bin Laden himself was hiding there.
It was hardly the spartan cave in the mountains that many had envisioned as bin Laden's hiding place. Rather, it was a mansion on the outskirts of the town's center, set on an imposing hilltop and ringed by 12-foot-high concrete walls topped with barbed wire.
The property was valued at $1 million, but it had neither a telephone nor an Internet connection. Its residents were so concerned about security that they burned their trash rather than putting it on the street for collection the way their neighbors did. American officials believed that the compound, built in 2005, was designed for the specific purpose of hiding bin Laden.
Months more of intelligence work followed before American spies felt highly confident that it was indeed bin Laden and his family who were hiding there—and before President Obama determined that the intelligence was solid enough to begin planning a mission to go after the Al Qaeda leader.
On March 14, Obama held the first of what would be five national security meetings in the course of the next six weeks to go over plans for the operation.
The meetings, attended by only the president's closest national security aides, took place as other White House officials were scrambling to avert a possible government shutdown over the budget. Four more similar meetings to discuss the plan would follow, until President Obama gathered his aides one final time last Friday.
At 8:20 that morning, Obama met with Thomas Donilon, the national security adviser; John O. Brennan, the counterterrorism adviser; and other senior aides in the Diplomatic Room at the White House. The president was traveling to Alabama later that morning to witness the damage from last week's tornadoes. But first he had to approve the final plan to send operatives into the compound where the administration believed that bin Laden was hiding.
Even after he signed the formal orders authorizing the raid, President Obama chose to keep Pakistan's government in the dark about the operation. As a senior administration official put it, "We shared our intelligence on this compound with no other country, including Pakistan."