The timeline of the mission to kill Osama bin Laden

The mission to kill Osama bin Laden was years in the making, but began in earnest last fall with the discovery of a suspicious compound near Islamabad, and culminated with a helicopter based raid in the early morning hours in Pakistan Sunday.

"Last August, after years of painstaking work by our intelligence community, I was briefed on a possible lead to bin Laden. It was far from certain, and it took many months to run this thread to ground," President Obama told the nation in a speech Sunday night.

"Today, at my direction, the United States launched a targeted operation against that compound in Abbottabad, Pakistan. A small team of Americans carried out the operation with extraordinary courage and capability. No Americans were harmed. They took care to avoid civilian casualties. After a firefight, they killed Osama bin Laden and took custody of his body," he said.

Sitting in a row of chairs beside the podium were National Security Advisor Tom Donilon, Director of National Intelligence James Clapper, CIA Director Leon Panetta, Joint Chiefs Chairman Adm. Mike Mullin, Secretary of State Hillary Clinton, and Vice President Joe Biden. White House Chief of Staff Bill Daley and Press Secretary Jay Carney stood in the back with about a dozen White House staffers.

Since last August, Obama convened at least 9 meetings with national security principals about this operation and the principals met 5 times without the president, a senior administration official said. Their deputies met 7 times formally amid a flurry of other interagency communications and consultations.

ABC News reported that the principals’ meetings were held on March 14, March 29, April 12, April 19 and April 28.

Last week Obama finally had enough intelligence last to take action. The final decision to go forward with the operation was made at 8:20 AM on Friday, April 29 in the White House’s Diplomatic Room. In the room at the time were Donilon, his deputy Denis McDonough, and counterterrorism advisor John Brennan. Donilon prepared the formal orders.

On Sunday, Obama went to play golf in the morning at Andrews Air Force Base. He played 9 holes in chilly, rainy weather and spent a little time on the driving range, as well. Meanwhile, the principals were assembling in the situation room at the White House. They were there from 1:00 PM and stayed put for the rest of the day.

At 2:00, Obama met with the principals back at the White House. At 3:32 he went to the situation room for another briefing. At 3:50 he was told that bin Laden was "tentatively identified." At 7:01 Obama was told there was a "high probability" the high value target at the compound was bin Laden. At 8:30 Obama got the final briefing.

Before speaking to the nation, Obama called former presidents Bill Clinton and George W. Bush.

Three senior administration officials briefed reporters late Sunday night on the surveillance, intelligence, and military operations that ended with bin Laden’s death at the hands of U.S. operatives.

"The operation was the culmination of years of careful and highly advanced intelligence work," a senior administration official said.

The stream of information that led to Sunday’s raid began over four years ago, when U.S. intelligence personnel were alerted about two couriers who were working with al Qaeda and had deep connections to top al Qaeda officials. Prisoners in U.S. custody flagged these two couriers as individuals who might have been helping bin Laden, one official said

"One courier in particular had our constant attention," the official said. He declined to give that courier’s name but said he was a protégé of Khalid Sheikh Mohammed and a "trusted assistant" of Abu Faraj al-Libbi, a former senior al Qaeda officer who was captured in 2005.

"Detainees also identified this man as one of the few couriers trusted by bin Laden," the official said. The U.S. intelligence community uncovered the identity of this courier four years ago, and two years ago, the U.S. discovered the area of Pakistan this courier and his brother were working in.

In August 2010, the intelligence agencies found the exact compound where this courier was living, in Abbottabad, Pakistan. The neighborhood is affluent and many retired Pakistani military officials live there.

"When we saw the compound where the brothers lived, we were shocked by what we saw," one official said.

The compound was 8 times larger than the other homes around it. It was built in 2005 in an area that was secluded at that time. There were extraordinary security measures at the compound, including 12 to 18 foot walls topped with barbed wire.

There were other suspicious indicators at the compound. Internal sections were walled off from the rest of the compound. There were two security gates. The residents burned their trash. The main building had few windows.

The compound, despite being worth over $1 million, had no telephone or internet service. There’s no way the courier and his brother could have afforded it, the official said.

"Intelligence officials concluded that this compound was custom built to hide someone of significance," the official said, adding that the size and makeup of one of the families living there matched the suspected makeup of bin Laden’s entourage.

The intelligence community had high confidence that the compound had a high value target, and the analysts concluded there was high probability that target was bin Laden, one official said.

When the small team of U.S. operatives raided the compound in the early morning hours Sunday Pakistan time, they encountered resistance and killed three men besides bin Laden and one woman. The three men were the two couriers and one of bin Laden’s sons. The woman was being used as a human shield, one official said. Two other women were injured.

One U.S. helicopter was downed due to unspecified "maintenance" issues, one official said. The U.S. personnel blew up the helicopter before leaving the area. The team was on the ground for only 40 minutes.

A senior defense official told CNN that US Navy SEALs were involved in the mission.

No other governments were briefed on the operation before it occurred, including the host government Pakistan.

"That was for one reason and one reason alone. That was essential to the security of the operation and our personnel," one official said. Only a "very small group of people" inside the U.S. government knew about the operation. Afterwards, calls were made to the Pakistani government and several other allied countries.

"Since 9/11 the United States has made it clear to Pakistan that we would pursue bin Laden wherever he might be," one official said. "Pakistan has long understood we are at war with al Qaeda. The United States had a moral and legal obligation to act on the information it had."

Americans abroad should stay indoors be aware of the increased threat of attacks following bin Laden’s killing, the State Department said in a new travel warning issued Sunday night. State also issued a specific travel warning for Pakistan.

"Al Qaeda operatives and sympathizers may try to respond violently to avenge bin Laden’s death and other terrorist leaders may try to accelerate their efforts to attack the United States," one official said. "We have always understood that this fight would be a marathon and not a sprint."