By Brian Ross, Matthew Cole and Avni Patel
The United States had been trying to kill Osama bin Laden for 13 years, since the administration of President Bill Clinton.
"Bin Laden has been our national enemy self declared for far longer than any one person in our history," said Richard Clarke, an ABC News contributor who served as a counterterrorism advisor to Clinton and both presidents Bush.
For years the trail had gone cold, some thought he had left the region and Pakistani officials even claimed bin Laden must be dead. In the end he was found in a house where he may have been living for as many as six years, almost next door to Pakistani military installations and less than 100 miles from the Pakistani capital of Islamabad.
The son of a prominent and wealthy Saudi family, bin Laden first went to Afghanistan to fight the Russians but then turned on the United States.
On his orders thousands died, in the 1998 attacks on two U.S. embassies in Africa, in the attack on the USS Cole in Yemen in 2000, and the 9/11 attacks of which he seemed so proud. Bin Laden boasted on tape that "We calculated in advance the number of casualties."
The discovery of bin Laden's hiding place in a million-dollar mansion in Pakistan was the result of a masterful CIA intelligence operation that focused on the courier who was his connection to the outside world.
"We had to piece it together," explained John Brennan, counterterrorism advisor to President Obama, "get [the courier's] nom de guerre, associate it with a real name and track it until we got to the compound."
Every video or audio message recorded by bin Laden went by courier, so each new message became an opportunity for the CIA to find him.
"That was his Achilles heel," said John Nagl, president of the Center for a New American Security and former lieutenant colonel in the U.S. Army. "We were able to use the information provided by tracking his couriers to hunt him down and bring him to justice."
U.S. officials say detainees held at Guantanamo helped lead them to the courier.
In one early clue, according to a secret Pentagon cable made public by Wikileaks, senior Al Qaeda commander Abu al Libi told interrogators he became "the official messenger" for bin Laden and for a year in 2003 "moved his family to Abbottabad, Pakistan" -- the city near Islamabad where bin Laden was killed Sunday.
By August of last year, the CIA had a sharp focus on a newly built compound in the Abbottabad, suspicious of its large size and extensive security features, including a seven-foot wall on the terrace so the very tall bin Laden could be outside without being seen.
A family of the same size as bin Laden's was seen here, although bin Laden himself was never actually spotted.
But since August he had sent out, at least two new taped messages. One of them, remarkably, last October, focused on the severe flooding that had just occurred in the Abbottabad region.
Finding Osama Bin Laden
Bin Laden had long been said to be in the mountainous region along the Afghanistan, Pakistan border, hiding in a cave as the U.S. sought to kill him with drone strikes from above. Instead, he was in a house with many peculiar features that brought it to the attention of U.S. authorities.
After locating the Al Qaeda courier in 2009 and then tracking him to the structure in 2010, the CIA noted that the house, built in 2005, had high exterior walls topped with barbed wire, high windows and few points of access. Residents burned their trash instead of putting it out. U.S. officials wondered if the extra seven-foot-high wall on a third-floor terrace was built to shield a man as tall as bin Laden, whose height was estimated at between 6'4" and 6'6".
The CIA began to believe that a high-value target was in the house. A CIA "red team" assigned to assess the house decided that it could well be sheltering bin Laden, even though he'd never been seen in the compound.
The CIA was responsible for "finding" and "fixing" the target, said a U.S. official, and the military "finished" the job.
According to U.S. officials, the Navy's SEAL Team Six practiced the assault in a replica of the compound built inside the United States.
Late Sunday night local time, two U.S. helicopters from Joint Special Operations Command (JSOC) and carrying Team Six SEALs flew in low from Afghanistan and swept into the compound. As CIA director Leon Panetta listened in, the Navy SEALs stormed the compound and engaged bin Laden and his men in a firefight, killing bin Laden and all those with him.
Two Bin Laden couriers were killed, as was Osama Bin Laden's son Khalid and a woman. Two women were injured. Children were present in the compound but were not harmed. U.S. officials said that bin Laden was asked to surrender but did not. He was shot in the head and then shot again to make sure he was dead.
The raid began on the smaller of two buildings in the compound, where the couriers were believed to live. The raid then moved to the larger three-story building. The couriers were killed downstairs, while bin Laden was upstairs.
After the raid, blood covered the floor of one room to the right inside the sprawling larger structure. In another room to the left that held a small kitchenette, broken computers could be seen, minus their hard drives. The SEALs also recovered papers, CDs, laptops, which were taken away for analysis.
One of the U.S. Blackhawk helicopters was damaged but not destroyed during the operation, and U.S. forces elected to destroy it themselves with explosives. At least a dozen individuals who were present in the compound were left flex cuffed by the side of the road by the SEALs when they departed, according to a senior administration official.
The Americans took bin Laden's body into custody after the firefight, taking it back to Afghanistan by helicopter, and confirmed his identity. His DNA matched DNA taken from multiple bin Laden relatives with almost 100 percent certainty, and his body was found to be more than 6'4". He was also identified by two women at the compound after he was killed, and via facial recognition analysis from photos sent back to CIA headquarters.
A U.S. official said bin Laden was later buried at sea in accordance with Islamic practice at 2 a.m. Washington time. Bin Laden's body was taken to the U.S.S. Carl Vinson, a U.S. aircraft carrier in the North Arabian Sea, according to officials. His body was washed and wrapped in the prescribed way. A military officer read religious remarks that were translated by a native Arabic speaker before bin Laden's remains were sent into the deep.
Remarkably, bin Laden was hiding almost under the nose of the Pakistani military, which has a major garrison in Abbottabad and the Pakistani version of West Point. A senior U.S. official says the U.S. government believes that bin Laden may have been living in the house ever since it was built in 2005.
U.S. officials say Pakistan was not informed in advance of the military operation inside their borders. The U.S. team was back inside Afghanistan before 6 p.m. Washington time.
Jake Tapper and Luis Martinez contributed to this report.