The trail that led to Osama bin Laden began before 9/11, before the terror attacks that brought the son of a Saudi construction magnate to prominence. The chase grew more urgent last fall, when U.S. intelligence discovered an elaborate compound in Pakistan, a clue that eventually culminated in Sunday’s raid on a fortified and isolated fortress in the Pakistani city of Abbottabad.
Details of the hunt for and killing of the 54-year-old bin Laden were still being assembled Monday, but briefings by senior White House and CIA officials filled in some gaps in the account of the investigation and death of the world’s most-wanted terrorist.
U.S. intelligence officials were aware of bin Laden’s growing radicalism before the attacks of Sept. 11, 2001, and began assembling a dossier on him.
"From the time that we first recognized bin Laden as a threat, the U.S. gathered information on people in bin Laden's circle, including his personal couriers," a senior official in the Obama administration said in a background briefing from the White House early Monday.
After the Sept. 11, attacks, "detainees gave us information on couriers. One courier in particular had our constant attention. Detainees gave us his nom de guerre, his pseudonym, and also identified this man as one of the few couriers trusted by bin Laden."Video: 2011: Obama confirms bin Laden is dead
In 2007, the U.S. learned the man's name.
It was not immediately clear where the information that opened the end game was obtained. The New York Times reported Monday that detainees at the military prison in Guantanamo Bay, Cuba, gave the courier’s pseudonym to interrogators and identified him as a protégé of Khalid Shaikh Mohammed, the confessed mastermind of the Sept. 11 attacks. But the Associated Press quoted unidentified U.S. officials as saying that CIA interrogators at secret prisons developed strands that led to bin Laden.
In 2009, "we identified areas in Pakistan where the courier and his brother operated. They were very careful, reinforcing belief we were on the right track."
In August 2010, "we found their home in Abbottabad," not in a cave, not right along the Afghanistan border, but in an affluent suburb less than 40 miles from the capital.
"When we saw the compound, we were shocked by what we saw: an extraordinarily unique compound."
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The plot of land was roughly eight times larger than the other homes in the area. It was built in 2005 on the outskirts of town, but now some other homes are nearby.
"Physical security is extraordinary: 12 to 18 foot walls, walled areas, restricted access by two security gates." The residents burn their trash, unlike their neighbors. There are no windows facing the road. One part of the compound has its own seven-foot privacy wall.
And unusual for a compound valued at more than $1 million: It had no telephone or Internet service.
This home, U.S. intelligence analysts concluded, was "custom built to hide someone of significance."
Besides the two brothers, the U.S. "soon learned that a third family lived there, whose size and makeup of family we believed to match those we believed would be with bin Laden. Our best information was that bin Laden was there with his youngest wife."
There was no proof, but everything seemed to fit: the security, the background of the couriers, the design of the compound.
"Our analysts looked at this from every angle. No other candidate fit the bill as well as bin Laden did," an official said.
"The bottom line of our collection and analysis was that we had high confidence that the compound held a high-value terrorist target. There was a strong probability that it was bin Laden."
That conclusion was reached in mid-February, officials said. Beginning in mid-March, the president led five National Security Council meetings on the plans for an operation.
Few in the know
On Friday, the president gave the order.
This information was shared "with no other country," an official said. "Only a very small group of people inside our own government knew of this operation in advance."
With bin Laden believed found, focus shifted to taking him out. A senior U.S. security official told Reuters that it was a "kill operation," removing the option for the team to simply capture bin Laden. Other US officials have publicly said that bin Laden could have been taken alive if he did not resist capture.
Bin Laden did not surrender, retired U.S. Army general Barry McCaffrey told NBC News.
"His security agents had been told to kill him if it looked like they were about to lose him to a U.S. snatch operation," he said.
Senior U.S. officials told NBC News Monday that CIA Director Leon Panetta had overall command of the operation.
The officials, both in the intelligence community and the Pentagon, said Panetta ran the operation from the CIA Directors conference room on the seventh floor for the CIA.
With Obama having authorized the operation, Panetta gave the order at midday Sunday for the joint special operations-military team that carried out the assault to raid the compound, the officials said. A senior U.S. official declined comment on whether CIA officers were on hand at the site, but Panetta's role as commander would suggest they were. The CIA and special operations forces have worked together for years in counterterrorism operations.
US officials watch in real time
According to current and former officials, Panetta was able to watch the operation in real time from the CIA, conferring live with Vice Adm. William H. McRaven, head of the Joint Special Operations Command, who was in Afghanistan. A live video feed of the assault was available in both in the conference room and at the Situation Room at the White House, narrated by McRaven. One official described two moments in particular as "heart-stopping": the moment the choppers arrived on the scene, and when they left the country.
Obama and the Director of National Intelligence, James Clapper, were among those on hand in the Situation Room. One official said it is unlikely that the entire video will be released because it contains operational information.
Following the death of bin Laden, a loud cheer went up from the CIA officials assembled in the conference room, which is just off the director’s main office.Video: US official: Bin Laden 'was hiding in plain sight'
At the same time, attention turned to identifying the remains as bin Laden. First, the commander on the ground (whose name has not been released) made a visual identification. Then, a digital image of bin Laden's remains was fed back to the CIA, where it was processed through a facial recognition system.
For a successful kill or capture, the code word for the U.S. forces on the ground was "Geronimo," sources told NBC News. When the mission was completed, the ground commander transmitted, "For God and country, Geronimo, Geronimo, Geronimo."
Also, bin Laden's' widow, a Yemeni, identified the remains as those of her husband. In addition to bin Laden, one of his adult sons, probably 19 year old Hamza Bin Laden, was killed as were a courier and the courier's brother. Bin Laden's widow remains in Pakistan, the officials said.
When the remains arrived in Afghanistan, an initial DNA test showed a high correlation of a match with the DNA on file. Saudi government had supplied the DNA long ago, having secured it from members of the bin Laden family. Bin Laden is one of 53 children of the late Mohammed Bin Laden. Results of a more complete DNA testing later confirmed the identity with "100 percent certainty," the officials said.
A burial at sea
Early Monday, an official told NBC News that bin Laden's body had already been buried at sea — eliminating the possibility of a burial shrine.
Islamic tradition calls for a body to be buried within 24 hours, but finding a country willing to accept the remains of the world's most wanted terrorist would have been difficult, a senior administration official said.
According to the White House briefing, the military operation went smoothly except for a helicopter landing that was not part of the original plan. The choppers were only intended to hover over the scene, but due to a technical malfunction, one of them landed or fell — "not a crash," the official said — so the military dispatched a third "emergency" helicopter to the scene.
"This operation was a surgical raid by a small team designed to minimize collateral damage. Our team was on the compound for under 40 minutes and did not encounter any local authorities."
The special ops team carrying out the mission was not certain if it even would encounter bin Laden in the compound until forces came face-to-face with him.
Video: Death of bin Laden
Two dozen SEALs in night-vision goggles dropped into the high-walled compound in Pakistan by sliding down ropes from Chinook helicopters in the overnight raid, an official told the Associated Press.
"If we had the opportunity to take bin Laden alive, if he didn't present any threat, the individuals involved were able and prepared to do that," Obama's counterterrorism adviser John Brennan said Monday. "We had discussed that extensively in a number of meetings in the White House and with the president. ... There was a firefight. He therefore was killed in that firefight."
Shot in the eye
"He did resist the assault force, and he was killed in a firefight," an official said. NBC News reported that he was shot in the left eye.
Later, White House officials said that bin Laden resisted, but was not armed.
Four adult males were killed: bin Laden, his son and the two couriers.
"One woman killed when used as a shield," and other women were injured, the officials said. The women's names were not given; it's not clear whether bin Laden's wife was among them.
The team blew up the disabled chopper upon their departure with bin Laden's remains, which resulted in a "massive explosion," the official told NBC.
Pakistan officials were unaware of the operation and scrambled fighter jets after getting reports of the explosion, according to the U.S. officials. But the U.S. helicopters were able to leave without further incident, the official said.
The Pakistanis "had no idea about who might have been on there, whether it be U.S. or somebody else," Obama's counterterrism adviser Brennan said. "So we were watching and making sure that our people and our aircraft were able to get out of the Pakistani airspace, and thankfully there was no engagement with Pakistani forces."
No U.S. personnel died.
'The single greatest victory'
White House officials proclaimed bin Laden's death "the single greatest victory in the U.S.-led campaign against al-Qaida," as one called it.
The officials also said they expect attacks from bin Laden's loyalists who may step up the timing of previously planned operations.
"In the wake of this operation, there may be a heightened threat to the U.S. homeland. The U.S. is taking every possible precaution." The State Department has sent advisories to embassies worldwide and has issued a travel ban for Pakistan.
"Although al-Qaida will not fragment immediately," an official said, "the death of bin Laden puts al-Qaida on a path of decline that will be difficult to reverse."
Msnbc.com's Bill Dedman and Robert Windrem, NBC News investigative producer for special projects, contributed to this report.
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