An old friend's innocuous, catch-up phone call to Abu Ahmed al-Kuwaiti, the main Pakistani courier for Osama bin Laden, led US forces to his hideout in Pakistan, according to a US media report.
The call marked a key moment in the decade-long US search for Al Qaeda's founder, the Washington Post reported citing US officials.
US intelligence agencies had been hunting for Kuwaiti for at least four years. The call with the friend gave them the number of the courier's cellphone. Using a vast number of human and technical sources, they tracked Kuwaiti to the compound, it said.
The main three-story building, which had no telephone lines or internet service, was impenetrable to eavesdropping technology deployed by the National Security Agency. US officials were stunned to realise that whenever Kuwaiti or others left the compound to make a call, they drove some 90 minutes away before even placing a battery in a cellphone, the Post said.
Turning on the phone made it susceptible to the kind of electronic surveillance that the residents of the compound clearly wished to avoid. As intelligence officials scrutinised satellite images of the compound, they saw that a man emerged most days to stroll the grounds of the courtyard for an hour or two, the Post said.
The man walked back and forth, day after day, and soon analysts began calling him "the pacer." The imagery never provided a clear view of his face. The pacer never left the compound. His routine suggested he was not just a shut-in but almost a prisoner.
Was the pacer bin Laden? A decoy? A hoax? A setup?
Finally several assessments concluded there was a 60 to 80 percent chance that bin Laden was in the compound. Michael
Leiter, the head of the National Counterterrorism Centre, put the probability at about 40 percent, the Post said.
When a participant at a White House meeting suggested that was a low chance of success, Leiter, according to the Post said, "Yes, but what we've got is 38 percent better than we have ever had before."
Officials cited by the Post said Obama's national security advisers were not unanimous in recommending he go ahead with the raid option. But he did and approved the raid at 8:20 a.m. on Friday.