When one of Osama Bin Laden's aides made a phone call last year, he unwittingly led U.S. pursuers to the doorstep of his boss, the world's most wanted terrorist.

That phone call became a key break in the search for the world's top terrorist, US officials recounted. It led U.S. intelligence to a walled compound in northeast Pakistan, where eventually a special team of US forces shot him.

The violent final minutes were the culmination of years of intelligence work.

In order for bin Laden to get messages in and out, he needed to rely on a close network of trusted couriers. Not even his top officials knew where he was or could communicate with him directly.

But in a secret CIA prison in Eastern Europe years ago, al-Qaida's No. 3 leader, Khalid Sheikh Mohammed, gave US interrogators the names a number of authorities the nicknames of several of bin Laden's couriers.

Those names were among thousands of leads the CIA was pursuing in an investigation spanning nearly a decade.

One man, Abu Faraj al-Libi, stood out. Interrogators learned that he was promoted to succeed Mohammed as al-Qaida's operational leader and he received the word through a courier. If they could find that courier, they'd find bin Laden.

The revelation that intelligence gleaned from the CIA's operations was seen as vindication for some after years of global outrage.

Former Defense Secretary Donald Rumsfeld told Politico that structures and processes put into place by Bush are paying benefits.

Rumsfeld did not directly credit intelligence obtained in during the Bush administration as contributing to Sunday's operation. However he said it may very well have been from the interrogation process that took place under Bush.

But Mohammed did not reveal the names while being subjected to the simulated drowning technique known as waterboarding, former officials said.

He identified them many months later under standard interrogation, opening up the debate as to whether the harsh technique was a valuable tool.

CIA operatives could not find him immediately. But in the middle of last year, the courier had a telephone conversation with someone who was being monitored by U.S.

The courier was located somewhere away from bin Laden's hideout when he had the discussion, but it was enough to help intelligence officials locate and watch him.

In August 2010, the courier unknowingly led authorities to a compound in the northeast Pakistani town of Abbottabad, where al-Libi had once lived.

Officials knew of the place for years but never suspected it was where bin Laden was.

But the fact that no one came in or out, and there were no phones or Internet connections led he CIA soon believed that bin Laden was hiding in plain sight. But since bin Laden never traveled and nobody could get inside, it was uncertain.

Still officials realized this could represent the best chance ever to get to bin Laden.

By mid-February, the officials were convinced a high-value target was hiding in the compound. President Barack Obama wanted to take action.

They were confident and their confidence was growing: 'This is different. This intelligence case is different. What we see in this compound is different than anything we've ever seen before,' John Brennan, the president's top counterterrorism adviser, said Monday. I was confident that we had the basis to take action.

Options were limited. The compound was in a residential neighborhood in a sovereign country. If Obama ordered an airstrike and bin Laden was not in the compound, it would be a huge diplomatic problem. Even if Obama was right, obliterating the compound might make it nearly impossible to confirm bin Laden's death.

Said Brennan: The president had to evaluate the strength of that information, and then made what I believe was one of the most gutsiest calls of any president in recent memory.

Obama tapped two dozen members of the Navy's elite SEAL Team Six to carry out a raid with surgical accuracy.

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