Where Is Osama Bin Laden?

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As Osama bin Laden urges Americans to convert to Islam in a new video released Friday, the al Qaeda leader's location remains a mystery.

But informed sources tell CBS News U.S. intelligence believes Osama bin Laden is hiding out in the Chitral district of northern Pakistan. A number of reports from human sources, including some alleged sightings, have put him there, reports CBS News national security correspondent David Martin.

None of the reports has been independently confirmed, but there are enough of them to persuade intelligence analysts that it's his most likely location.

Chitral is a remote, rugged area governed by tribes that will not allow even the Pakistani army to operate there.

"They have a code of hospitality for guests, and they've probably also gotten a fair amount of money from bin Laden," says Daniel Benjamin of the Brookings Institute, who tracked bin Laden during the Clinton administration. He believes bin Laden is surrounded by body guards armed with surface-to-air missiles and good intelligence.

"I think it's quite likely he has a very good early warning system (and) that there are perimeters set up so people know who's coming and going in the area that he's living," Benjamin said.

Before 9/11, bin Laden's deputy Ayman al Zawahiri always seemed to be at his side. But no longer.

"They're separated for good reasons," says Benjamin. "Most countries don't let their top two people travel together or undertake anything that would be risky together."

Last year, a U.S. missile strike narrowly missed Zawahiri after the CIA tracked him to a meeting of senior al Qaeda operatives south of Chitral. Al Qaeda seems willing to risk Zawahiri in order to protect bin Laden.

"It seems like they've made a decision that bin Laden will have a much higher level of operational security," Benjamin says. "Zawahiri will take more risks and is probably in a more accessible place."

So far, it's working. The only proof U.S. intelligence has that bin Laden is even alive are his own videos.