As helicopters descended out of darkness on the most important counterterrorism mission in U.S. history, President Barack Obama watched from the White House.

It was an operation so secret, only a select few U.S. officials knew what was about to happen.

And after giving the go-ahead for the mission, the president kept a poker face over the weekend while consoling tornado victims in the South, delivering a college commencement address and cracking jokes at a black-tie dinner for Washington correspondents.

The location of the raid was a fortified compound in the affluent Pakistani town of Abbottabad, about 150 kilometres north of Islamabad. The target: Osama bin Laden.

Intelligence officials discovered the compound in August while monitoring an al-Qaeda courier, a Kuwaiti-born man named Sheikh Abu Ahmed.

Ahmed was a shadowy figure for U.S. intelligence, someone it took many years to identify. For a long time, intelligence officials knew him only by his nom de guerre, Abu Ahmed al-Kuwaiti.

The first indications about his significance came shortly after the Sept. 11, 2001, terrorist attacks from CIA detainees who told interrogators the courier was so trusted by bin Laden that he might be living with the al-Qaeda leader.

Ahmed, his brother and an unidentified woman were killed along with bin Laden in the attack on the compound.

Nestled in an affluent neighbourhood, the compound was surrounded by walls as high as 5½ metres, topped with barbed wire. Two security gates guarded the only way in. A third-floor terrace was shielded by a 2.1-metre privacy wall. No phone lines or internet cables ran to the property. The residents burned their garbage rather than put it out for collection.

Accidental liveblog? Sohaib Athar's profile picture (@ReallyVirtual) One witness unknowingly posted live updates of the raid on his Twitter account Sunday evening. Sohaib Athar, whose profile says he is an "IT consultant taking a break from the rat-race by hiding in the mountains with his laptops," inadvertently broke word of the event with one tweet: "Helicopter hovering about Abbottabad at 1 a.m. (is a rare event)." That was soon followed by a "huge window shaking bang in Abbottabad. I hope it is not the start of something nasty." As he realized the sounds he was hearing were related to Osama bin Laden's death after U.S. President Obama confirmed it, he tweeted: "Uh oh, now I'm the guy who liveblogged the Osama raid without knowing it." The number of people following his formerly obscure account exploded to more than 33,000 within hours of his initial tweet. "Bin Laden is dead. I didn't kill him. Please let me sleep now," he tweeted before signing off at around 8 a.m. ET on Monday.

Intelligence officials believed the million-dollar compound was built five years ago to protect a major terrorist figure. The question was, who?

The CIA asked itself again and again who might be living behind those walls. Each time, officials concluded it was almost certainly bin Laden.

Many meetings held

By mid-February, intelligence from multiple sources was clear enough that Obama wanted to "pursue an aggressive course of action," a senior administration official said. Over the next 2½ months, Obama led five meetings of the National Security Council focused solely on whether bin Laden was in the compound and, if so, how to get him, the official said.

Normally, the U.S. shares its counterterrorism intelligence widely with trusted allies in Britain, Canada, Australia and elsewhere. And normally, the U.S. does not carry out ground operations inside Pakistan without collaboration with Pakistani intelligence. But this mission and the need for secrecy were too important. No allies were made aware of the plan, the White House confirmed Monday.

It was a mission that required surgical accuracy, even more precision than could be delivered by the government's sophisticated Predator drones. To execute it, Obama tapped a small contingent of U.S. forces under the command of CIA director Leon Panetta, whose analysts monitored the compound from afar.

Panetta was directly in charge of the team, a U.S. official said, and his conference room was transformed into a command centre.

Details of exactly how the raid unfolded remain murky, but a few things are known.

On Friday morning, Obama approved the mission before leaving Washington to inspect tornado damage in Alabama. A small contingent of the navy's elite SEAL Team Six, a top military counterterrorism unit, was approved to carry out the mission.

A map of the compound where Osama bin Laden was living in Abbottabad. ((CBC))

On Sunday, Obama cut short a round of golf to return to the White House for a meeting where he and top aides reviewed final preparations. The raid began within hours of that final meeting. It involved four U.S. Black Hawk helicopters, about two dozen troops and took about 40 minutes from start to finish.

"The minutes passed like days," John Brennan, the U.S. government's counterterrorism chief, said at a news conference Monday, adding that Obama monitored the raid from the White House Situation Room and expressed relief that no American lives had been lost.

White House officials said two dozen SEALs in night-vision goggles dropped into the high-walled compound in Pakistan by sliding down ropes from helicopters.

One of the helicopters broke down and was later destroyed so it wouldn't fall into enemy hands. Among many others, the tailed al-Qaeda courier and bin Laden's son are also believed to have been killed during the mission. The compound itself belonged to the courier, the White House said.

A Pentagon official said a woman identified bin Laden name during the U.S. raid.

Brennan said bin Laden used human shields, some of whom were women, in his final moments.

"He was hiding behind women who were put in front of him as a shield," Brennan told the news conference. "I think that speaks to just how false his narrative has been over the years."

Osama bin Laden went down firing at the Navy SEALs who stormed his compound.

"He was engaged in a firefight," Brennan said.

An official familiar with the operation says bin Laden was hit by a barrage of carefully aimed return fire. Three other people were also killed: two of bin Laden's couriers and an unidentified woman.

The official spoke on condition of anonymity because aspects of the operation remain classified.

Senior U.S. officials said bin Laden's body was transferred to the aircraft carrier USS Carl Vinson where traditional Islamic procedures for handling the remains were followed, including washing the corpse, placing it in a white sheet and committing the body to the waters of the North Arabian Sea.

When Panetta and his team received word that bin Laden was dead, cheers and applause broke out across the conference room.

Later that evening, Obama delivered a public address to the world, announcing bin Laden's death. White House officials later revealed DNA testing had confirmed his identity.

Compound close-up

Click on the graphic below to get a zoomed in view of the Abbottabad compound that housed Osama bin Laden.