Timeline: The intelligence hunt leading to Bin Laden

A man walks near the compound in Abbottabad where Osama Bin Laden was killed. File photo US intelligence agencies monitored the compound for months before the raid

The moment that led to Osama Bin Laden's death in a raid by US Navy Seals was a culmination of years of intelligence gathering.

The search lasted several years and ended at a secure compound in the Pakistani town of Abbottabad in the early hours of 2 May 2011.

Here is a breakdown of the pivotal moments in the process.

2002

Following the 11 September 2001 attacks and the subsequent invasion of Afghanistan, the Central Intelligence Agency (CIA) and US military began rounding up suspected al-Qaeda members and interrogating them either at the Guantanamo Bay detention centre in Cuba, or at secret overseas prisons. Officials began compiling information about major players, foot soldiers, couriers and money men.

Some prisoners - often after being subjected to "Enhanced Interrogation Techniques" (EITs) such as water-boarding and sleep deprivation - revealed that Bin Laden had a trusted courier whose pseudonym was Abu Ahmed al-Kuwaiti.

2003

Khalid Sheikh Mohammed, the alleged mastermind of 9/11, was captured in the Pakistani city of Karachi in March 2003 and sent to a secret prison in Thailand.

Khalid Sheikh Mohammed (2003) Mohammed eventually confirmed knowing al-Kuwaiti

When asked about the courier's name by interrogators, he claimed never to have heard it, raising suspicions and suggesting he was probably an important figure.

Jose Rodriguez, who was director of the CIA's Counterterrorism Center (CTC) from 2002 to 2005, told Time magazine that Mohammed eventually provided information on the courier "weeks or months after he was subjected to EITs".

Mohammed confirmed knowing al-Kuwaiti but denied he had anything to do with al-Qaeda.

2004

Top al-Qaeda operative Hassan Ghul was captured in January 2004 in northern Iraq. He told interrogators at a CIA "black site" where he was held that al-Kuwaiti was someone crucial to al-Qaeda and its leader. In particular, Ghul said, the courier was close to Abu Faraj al-Libi, who succeeded Khalid Sheikh Mohammed.

"Hassan Ghul was the linchpin," an official told the Associated Press.

2005

Abu Faraj al-Libi was captured in May 2005 in the northern Pakistani city of Mardan.

Abu Faraj al-Libi (2005) Libi revealed the courier carried messages from Bin Laden to the outside world every two months

Under CIA interrogation, he admitted that when he was promoted to succeed Khalid Sheikh Mohammed he received the word through a courier, but made up a name and denied knowing al-Kuwaiti - much like Mohammed did.

But Mr Rodriguez said that after a week of Enhanced Interrogation Techniques - though not water-boarding - Libi acknowledged knowing al-Kuwaiti and provided "key" information on him. Libi revealed that the courier carried messages from Bin Laden to the outside world only every two months or so, Mr Rodriguez added, suggesting Bin Laden was not running al-Qaeda's operations.

However, Mr Rodriguez's assertion that information obtained following the use of ETIs was decisive in finding Bin Laden was denied by the White House.

The year also saw the CIA place more case officers on the ground in Pakistan and Afghanistan.

They discovered the courier's family name and the National Security Agency (NSA) set to work intercepting telephone calls and emails between his family and anyone inside Pakistan. From there they got his full name, Sheikh Abu Ahmed, a Pakistani man who was born in Kuwait.

2009

US intelligence agencies finally identified an area of Pakistan where the courier and his brother were operating, but could not pinpoint exactly where they lived.

Meanwhile, the intelligence arm of the Pakistan military, the Inter Services Intelligence Directorate (ISI), provided information about the compound in Abbottabad where Bin Laden was found, according to the Pakistani foreign ministry.

"The intelligence flow indicating some foreigners in the surroundings of Abbottabad continued till mid-April 2011," a statement said.

July 2010

Satellite phone calls that the courier made - reportedly to known al-Qaeda associates in the cities of Kohat and Charsada in Pakistan's Khyber Pakhtunkhwa province - were monitored by the US National Security Agency (NSA).

Pakistani agents working for the CIA then spotted al-Kuwaiti driving his vehicle near the northern city of Peshawar. They began tracking his movements.

August 2010

Al-Kuwaiti unknowingly led the agents to a compound in Abbottabad, 56km (35 miles) north of Islamabad and about a kilometre from the Pakistan Military Academy, with a three-storey building inside and concrete walls as high as 5.5m (18ft).

The compound was so large, secluded and secure that analysts concluded it was being used to shelter a "high-value target", perhaps even Bin Laden.

CIA Director Leon Panetta briefed President Barack Obama and his most senior national security aides, including Vice-President Joe Biden, Secretary of State Hillary Clinton and Defence Secretary Robert Gates.

Autumn 2010

US intelligence agencies continued monitoring the compound to ascertain whether Bin Laden was located inside.

A Navy Seals team trains. File photo The Navy Seals team rehearsed the Abbottabad raid at training facilities

A safe house was set up in Abbottabad, from which the CIA officers were able to observe daily activities at the compound for some months, a US official was quoted as saying in the US media.

The official said the CIA used cameras with telephoto lenses, infrared imaging equipment and also high-tech eavesdropping tools to try to pick up voices from inside the compound, which had neither a telephone line nor internet connections.

The National Geospatial-Intelligence Agency (NGA) also developed highly detailed maps of the area and imagery of the compound for the CIA. "Patterns of life" there were recorded.

Mr Panetta and CIA officials discussed whether to mount a surveillance operation on the ground, but it was feared the occupants might notice and flee.

The CIA also ruled out bringing in the Pakistani authorities because "it was decided that any effort to work with the Pakistanis could jeopardise the mission", Mr Panetta told Time. "They might alert the targets."

February 2011

By mid-February, following a series of meetings at the White House that included the president, it was determined that there was a "sound intelligence basis" for developing courses of action to pursue Bin Laden at the location.

Mr Panetta called the commander of the US military's Joint Special Operations Command (JSOC), Vice Admiral William McRaven, to the CIA's headquarters in Langley, Virginia, to ask him to begin planning a strike.

After several weeks, he came up with three proposals, a high-altitude bombing raid by B-2 bombers, a "direct shot" with cruise missiles, and a helicopter assault using a team of US commandos. The first two might have obliterated the compound and risked causing much "collateral damage".

14 March

President Obama chaired his first of five National Security Council (NSC) meetings to discuss the options presented by Adm McRaven, because evidence was mounting that Bin Laden was indeed in the compound.

Administration officials were reportedly split on whether to launch a commando assault, order an air or missile strike, or wait and continue monitoring until they were more confident that Bin Laden was there.

22 March

The president asked his advisers their opinions on the options at an NSC meeting.

Mr Gates was sceptical about a helicopter assault, calling it risky, and instructed military officials to look at using smart bombs, according to the New York Times. But he was later told it would take some 32 bombs of 2,000 pounds each, which would have created a giant crater and destroyed any bodies.

A helicopter assault emerged as the favourite, and the Navy Seals team - reportedly Seal Team Six (ST6), officially known as the Naval Special Warfare Development Group - began rehearsing the operation at training facilities, where models of the compound were built. They were not told who their target was initially.

26 April

Mr Panetta held a meeting with 15 aides to assess the credibility of the intelligence on the compound they had collected. They had significant "circumstantial evidence" that Bin Laden was there, but no satellites had been able to photograph him or any members of his family, Mr Panetta said.

The CIA chief concluded that the evidence was strong enough to risk the raid, despite the fact that his aides were only 60-80% confident that Bin Laden was there, and decided to make his case to the president.

28 April

Mr Panetta told the president and his national security advisers at an afternoon meeting in the White House Situation Room that it was time to decide. They discussed the negative scenarios, and the room was divided 50-50 on whether to go for a helicopter assault or a missile strike, one official said.

"When you put it all together we have the best evidence since [the 2001 battle of] Tora Bora [where Bin Laden was last seen], and that then makes it clear that we have an obligation to act," Mr Panetta said he told the room.

Eventually, Mr Obama concluded the meeting by saying: "I'm not going to tell you what my decision is now - I'm going to go back and think about it some more." But he added: "I'm going to make a decision soon."

29 April

At about 0800 EST, shortly before he boarded a helicopter that would take him to tour tornado damage in Alabama, President Obama called his senior aides to the White House Diplomatic Room. He handed over a signed order instructing them to proceed with a helicopter assault. "It's a go," he said.

Mr Panetta ordered Adm McRaven to undertake the mission at 1322 EST. He told him "to go in there [and] get Bin Laden, and if Bin Laden isn't there, get the hell out!"

30 April

Mr Obama took a break from rehearsing for the White House Correspondents Dinner that night to call Adm McRaven to wish him luck.

1 May

All West Wing tours were cancelled so tourists and visiting celebrities would not see high-level national security officials gathered in the Situation Room monitoring the feeds they were getting from Mr Panetta, who was based at Langley.

Between 1600 and 1640 EST - about 0100-0140 on 2 May Pakistan time - US commandos raided the compound.

At 2335 EST, Mr Obama announced that Bin Laden was dead.

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