On the fifth anniversary of the Sept. 11, 2001, attacks, the resounding question: Where is Osama bin Laden?
Just as urgent is another question: Why has U.S. intelligence failed to find him?
A decade into a manhunt that is surely the most costly and complex in history, senior U.S. diplomats and intelligence officials can only give you "guesstimates" when you ask about bin Laden's location.
The suppositions are generally similar: Very few people know his location, and he probably has only a couple bodyguards.
He never uses the phone or Internet, and likely lives in a dwelling that has no communications to the outside world.
He moves infrequently, if at all, but he's in a friendly area, where the locals would almost certainly protect him in a pinch.
Pressed harder, U.S. officials will sometimes reveal a discomforting fact: Other than that, they can't tell you much more.
For all the millions of dollars spent on spy satellites and phone tapping, for all the agents scouring the globe, and for all the millions in offered rewards, there has been no real-time information on the whereabouts of bin Laden since he slipped away from Tora Bora in December 2001, reportedly on the back of a donkey.
"Those who are trying to get him have very poor intelligence," said ABC News consultant Rahimullah Yusufzai. "They are not up to the mark."
The story of how a rich Saudi kid abandoned a life of excess to become one of Islam's most identifiable figures offers tantalizing clues to his continued ability to elude capture.
From his father -- the poor Yemeni immigrant turned multibillionaire builder and then Saudi king -- bin Laden drew his entrepreneurial spirit and his ability to network, creating a global terror system that now runs itself.
He learned life on the run during his years with the Afghan mujahedeen. It is now a fine-tuned lifestyle, say those who have met him.
According to some reports, he won't even wear a watch, fearing U.S. authorities could use it to track him.
"He has become very cautious, very careful about who gets access," Yusufzai said. "He does not use phones. He does not give interviews."
The latest video release from al Qaeda, shown Thursday, reinforces the general presumption that the world's most famous fugitive has carved out a lair for himself in the mountains between Pakistan and Afghanistan.
In it, you see the al Qaeda leader pick his way down boulder-strewn slopes, smile serenely to the 9/11 plotters, and address his followers inside a simple tent.
The border area is certainly lush with places to hide, and Pakistan's volatile tribal belt offers the added benefit of being off limits to American troops and intelligence agents.
"It has become what we call in the CIA 'a denied area,'" said former CIA agent and author Robert Baer.
"And it is impossible to find someone in a denied area."
Current estimates put bin Laden in the northern districts of the tribal belt, close to the border with volatile Kunar province in Afghanistan.
For about 10 months, U.S. intelligence maintained a small safe house in the Pakistani town of Chitral, near the edge of the tribal belt, where agents apparently stalked bin Laden with sophisticated listening devices.
In July, however, locals say that the operation closed and that the equipment was removed.
Did they conclude he wasn't there? Or were they simply looking in the wrong place?
Some analysts point out that all the high-value al Qaeda arrests have taken place in Pakistani cities and none in the tribal belt: Khalid Sheik Mohammed in Rawalpindi; Abu Zubaydah in Faisalabad; Ramzi bin al Shib in Karachi; and so on.
"There has been no concrete intelligence, or even simple logical rationale, to suggest that anyone of significance is in the [border] areas," said terrorism analyst MJ Gohel.
"Western surveillance efforts need to be directed towards the Pakistani cities and at the Pakistani terror groups closely allied to al Qaeda."
But searching for terrorists in Pakistan, U.S. and British officials say, is deeply hamstrung.
Pakistan's spy agency, the notorious ISI, insists on taking the lead role.
"It's like letting the fox guard the chicken coup," said a frustrated U.S. official. "We will never find Osama until the ISI wants us to."
For domestic, regional and political reasons, the Pakistani government has no good reason to hand over bin Laden, even if authorities here did know how to find him.
"He is a crazed murderer, but he is a symbol of resistance for Muslims," Baer said. "And while he remains a symbol, people are not going to want to turn him in."
Finally, bin Laden seems to be blessed with remarkable luck.
Botched attempts to catch him date back to the Clinton administration -- remember the cruise missiles that struck his camp in Khost in 1998 -- and each time he has made a remarkable getaway.
For his supporters, each great escape only heightens his David-vs.-Goliath status.
For those stalking him, it only reinforces their confidence that his luck is running out.
"I always come back to is this," said a senior U.S. official. "Bin Laden has to be right and get lucky every day. We just have to do it once."