"The way he is managing their affairs, the way he is controlling things, he is not an ordinary man," said one top Pakistani intelligence official. "He is very sharp and brave -- an unusual combination."
Sometimes Mohammed's escapes have been abetted by the caution of his pursuers. In one instance, in 1996, U.S. intelligence had determined that Mohammed was in Doha, Qatar. Some American officials wanted to organize what they call a "snatch and grab," essentially a commando raid, to seize him.
"Good intel had placed him in Qatar. This was, 'Oh my God! This bastard is in Doha -- let's get him," said one person involved in the investigation.
This plan was defeated when high-level managers complained during a White House meeting that it was too risky and might result in American deaths, according to two people involved in the decision. They said this failure to act decisively characterized the U.S. government's lack of a serious approach to terrorism before the Sept. 11 attacks.
"Look at what has happened in the last six years -- you would have to assume that he played a role in everything from that point on. We absolutely believe that," said Neil Herman, a former top FBI counter-terrorism officer. "He is right there. He is a common denominator. If he had been caught in 1996, who knows what could have been prevented."
Pakistani and American officials say catching Mohammed now could turn the tide in the war on terrorism. The senior Pakistani intelligence official said: "If you catch Khalid Shaikh at this point, you will break the backbone of the entire network."
Almost every Al Qaeda suspect whom the Pakistanis have arrested since last year has had some connection to Mohammed, authorities say. Many of those arrested have no links to one another, but they all know Mohammed.
Even those investigators who have been most involved in the hunt for Mohammed say they know very little about him. In the small, closed world of international counter-terrorism, he has become a mythic figure -- a ghost in the machine -- whose vague presence lurks behind innumerable plots but never comes completely into view.
Kuwait: Oil Town
Khalid Shaikh Mohammed was born in 1965, according to records, and reared in Fahaheel, a busy oil settlement south of Kuwait City, on the road to Saudi Arabia. The town was historically part of a sleepy agricultural zone on the edge of an oasis, a traditional site of palm and vegetable cultivation. Older Kuwaitis recall driving the route from Kuwait City through miles of desert, with the occasional vehicle, camel and Bedouin tent as the only landmarks.
