"He's a single individual who has a lot of money at his disposal, and a network of people who work with him and for him and who are willing to go out on a limb to hide him," Col. Roger King, a spokesman for the U.S. military at Bagram Air Base, near the Afghan capital Kabul, said Saturday. "Certainly, that makes it a challenge to catch him." 

Bin Laden apparently escaped an international dragnet at least three times before. 

In December 2001, U.S. and Afghan troops surrounded a giant cave complex in the eastern Afghan region of Tora Bora, and on Dec. 10 intercepted a radio transmission that was believed to have come from the al-Qaida leader. 

U.S. warplanes blanketed the area with bombs, but the Americans relied largely on local Afghan forces on the ground. Hundreds of al-Qaida suspects are believed to have escaped across the border into Pakistan, and bin Laden may have been among them. 

Intelligence officials believe bin Laden has been hiding in the mountains between the two countries ever since. He has not been seen since a November 2001 videotape, but several audiotapes reputedly made by the terror chief have been released in recent months. 

In August 1998, the Clinton Administration ordered a cruise missile strike on two of bin Laden's terrorist training camps in Afghanistan after al-Qaida orchestrated the bombings of two U.S. embassies in Africa. Bin Laden is believed to have been at the Zhawar Kili Al-Badr camp for a meeting with several of his top men, but left shortly before some 70 Tomahawk cruise missiles slammed into the dusty complex. 

Bin Laden could have been caught in Sudan in 1996, before the October 2000 bombing of the USS Cole, the Africa embassy bombings and the Sept. 11 attacks. 

Clinton administration officials have told The Associated Press they tried to convince authorities in bin Laden's native Saudi Arabia to allow Sudan to deport him for trial there. But the Saudis refused, fearing a trial would destabilize the country, the officials said on condition of anonymity. In May of that year he fled to Afghanistan. 

The near misses have given bin Laden an aura of invincibility among his supporters, but that could be fading under the pressure of the biggest manhunt in history. 

Bin Laden's Taliban protectors are gone, and top confidantes like Mohammed and former al-Qaida leader Abu Zubaydah are in U.S. custody. Mohammed Atef, al-Qaida's military chief, was killed in the U.S. bombing that ousted the Taliban, and another top al-Qaida operative was killed in Yemen in November when an unmanned U.S. Predator drone fired a missile at his car. 

"The people who have been helping him stay elusive are getting captured or killed, so the chances of him getting caught now are much brighter than they were six months ago," said security analyst Talat Massood, a retired Pakistani general. "Bin Laden has shown many times that he has the capacity to survive, but conditions are not favorable for him now. The noose is tightening." 

Michael Swetnam, a counterterrorism specialist at the Washington-based Potomac Institute for Policy Studies, said the United States is trying to act faster on information like that obtained in the Mohammed arrest. He said bin Laden has forced the change because of his ability to anticipate American intelligence. 

"It really is a chess game. He has escaped two or three times before, mostly because he has been a real student of our operational process," said Swetnam. "He slips through the cracks because he knows where the cracks are."