Washington:
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 sprawling mansion 35 miles north of the Pakistani capital, close to one of the hubs of American counterterrorism operations. The compound 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 the death of Osama bin Laden, and concluded one of history's most extensive and frustrating manhunts.
American officials said that Osama bin Laden was shot in the head after he tried to resist the assault force, and that one of his sons died along with him.
For nearly a decade, American military and intelligence forces have chased the specter of Osama bin Laden throughout Pakistan and Afghanistan, once coming agonizingly close and losing him in a pitched battle at Tora Bora, in the mountains of eastern Afghanistan. As Obama administration officials describe it, the real breakthrough came when they finally figured out the name and location of Osama bin Laden's most trusted courier, whom the Qaeda chief appeared to rely on to maintain contacts with the outside world.
Detainees at the Guantánamo Bay prison had given the courier's pseudonym to American interrogators, and said the manwas a protégé of Khalid Shaikh Mohammed, the confessed mastermind of the September 11 attacks.
American intelligence officials said Sunday night that 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.
Still, it was not until August when they tracked him to the compound in Abbottabad, a medium sized city about an hour's drive north of Islamabad, the capital.
C.I.A. analysts spent the next several weeks examining satellite photos and intelligence reports to determine who might be living at the mansion, and a senior administration official said that by September the C.I.A. had determined there was a "strong possibility" that Osama bin Laden himself was hiding there.
It was hardly the spartan cave in the mountains where many had envisioned Osama bin Laden hiding. Rather, it was a large mansion on the outskirts of the town 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.
American officials believed that the mansion, built in 2005, was designed for the specific purpose of hiding Osama bin Laden.
Months more of intelligence work would follow before American spies felt highly confident that it was indeed Osama bin Laden and his family who were hiding in the compound -- and before President Obama believed the intelligence was solid enough to begin planning a mission to go after the Al Qaeda leader.
On March 14, Mr. 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 aides scrambled 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.