Khalid Shaikh Mohammed's darkly imaginative mind has long been one of Al Qaeda's deadliest assets. Now that he is in custody, his extensive knowledge of Al Qaeda plots and tactics could pose a serious threat to the terrorist network.
Mohammed is likely to know the identities and locations of Al Qaeda operatives around the world, including members of any so-called sleeper cells hiding in the United States, intelligence officials and terrorism experts said.
His interrogation -- which already has begun at an undisclosed location -- thus might lead to an intelligence bonanza detailing Al Qaeda plots, finances, communications, safe houses and other operations that have helped sustain Al Qaeda since the loss of its sanctuary in Afghanistan.
Experts said Mohammed was so crucial to the network and his knowledge of its secrets so extensive that his arrest is certain to send ripples of panic to every corner of the organization, including Osama bin Laden's hiding place.
"Nobody's safe now," said Bob Baer, a former CIA officer who spent much of his career tracking terrorism. "They're going to have to move. Everything they considered reliable is gone -- safe houses, sources of money and the rest. They have to assume the worst."
Combined with previous arrests and strikes, Mohammed's capture all but eliminates an entire tier of the Al Qaeda hierarchy, stripping the network of its best minds for organizing and executing terrorist plots.
"It's the crown jewels of the organization's operational capacity," said Bruce Hoffman, an expert on terrorists who is Washington director of the Rand Corp. "The repercussions radiate in both directions. It cuts the senior leaders off from their conduit for orders to foot soldiers, and foot soldiers from guidance and planning and implementation of operations."
Experts cautioned that Al Qaeda is still an unparalleled threat because of its remarkable ability to replenish its ranks and its decentralized structure, which allows cells and plots to survive even decapitating blows.
"You weaken the body by cutting off the head, but you don't eliminate the danger. The problem is that the organization is not hierarchical," said Judge Jean-Louis Bruguiere, France's top anti-terrorism magistrate.
But many in the intelligence community said that the arrest is arguably the most significant in the history of counter-terrorism, and that capturing Bin Laden would be more important only in a symbolic sense.
"Beyond [Mohammed's] knowledge of current Al Qaeda plots, he's likely to know the identity and whereabouts of other top terror leaders around the world," said a U.S. official familiar with the capture. "His capture could lead to an information windfall that will lead to further successes against Al Qaeda."
Reports from Pakistan indicate that authorities confiscated a computer, computer discs and other evidence during the predawn raid in Rawalpindi. Such material in the past has provided the outlines of terrorist plots as well as phone numbers, addresses, phony IDs and other clues that have led to further arrests.
Mohammed is believed to have reported directly to Osama bin Laden in the past. The two were said to be together when Bin Laden first heard reports of the Sept. 11 attacks, and Mohammed might know Bin Laden's current -- or recent -- whereabouts. The CIA believes that Bin Laden is hiding in the rugged mountains between Pakistan and Afghanistan, but repeated raids in the area have failed to find him.
While Bin Laden is considered the inspirational leader and public face of Al Qaeda, captives and detainees have described Mohammed as a charismatic figure who operates in the shadows as a recruiter, coordinator and "field general."
Mohammed has overseen plots in Europe, the Middle East and Southeast Asia.
Even though he was on the run in Pakistan, French investigators say Mohammed organized and commanded last year's truck-bomb attack on a historic synagogue on the Tunisian island of Djerba that killed 21 people, coordinating a network that included a presence in France, Germany and Spain. Mohammed spoke to the suicide bomber by satellite phone shortly before the attack, according to investigators.
He has played a role in Al Qaeda's efforts to obtain chemical and biological weapons, as well as a so-called dirty bomb that uses conventional explosives to spread radioactive material.
Mohammed is also believed to be the direct commander of terrorist cells around the world.
"He's the guy who keeps the keys to the sleeper cells," said Vincent Cannistraro, a former CIA counter-terrorism official, referring to groups of militants who live ostensibly normal lives until called into action. "He knows where the sleeper cells are in the United States."
FBI Director Robert S. Mueller III told a Senate committee hearing last month that hundreds of Al Qaeda members might be in the United States. The administration this week lowered a terrorist alert that was based, in part, on fears that a sleeper cell had been activated and was planning an attack within the United States.
Cannistraro said Mohammed's arrest showed that U.S. intelligence and law enforcement agencies, especially the CIA and FBI, were achieving results.
"They've gone from being justly criticized for the failures that led to 9/11 to the point where capabilities and coordination have produced real results," he said.
Officials described Mohammed as one of the most prominent planners and organizers within Al Qaeda since 1993, when his nephew, Ramzi Ahmed Yousef, carried out the first bombing of the World Trade Center in New York.
Mohammed didn't necessarily conceive each attack, but his role in an aborted attempt to blow up 12 airliners over the Pacific in 1995 is believed to have been the genesis of the skyjacking and crashing of four passenger airliners in New York, the Washington area and Pennsylvania six years later.
He was a member of a triumvirate of operational figures that has now been eliminated from Al Qaeda's senior ranks, experts said. Mohammed Atef, Bin Laden's chief of military operations, was killed by a U.S. bomb during the war in Afghanistan. Abu Zubeida, who served as a field operations coordinator, was wounded and captured in a raid in Lahore, Pakistan, about a year ago.
A number of Al Qaeda's operational experts remain at large, including Saif Adel, an Egyptian who served as a senior military commander and is believed to have been involved in the bombings of the destroyer Cole in 2000 and the American embassies in Kenya and Tanzania in 1998.
Another is Tawfiq Attash Khallad, a Yemeni who is the suspected mastermind of the Cole bombing.
The arrest of Mohammed could spark a shake-up in Al Qaeda's structure and security.
"If someone who is as high a priority as Khalid Shaikh Mohammed can be apprehended, they have to wonder how good is their security, how likely is their longevity," said Hoffman, the expert on terrorists. "This may smoke them out. The more they move, the greater the chances of our detecting them."
In all, U.S. officials say they have captured or killed more than one third of the top two dozen Al Qaeda leaders or commanders around the world.
In addition to information on the Sept. 11 attacks, Mohammed probably holds answers to an array of tantalizing questions. He could provide a long-sought accounting of the chain of events that led to the first World Trade Center bombing in 1993. And he undoubtedly has extensive knowledge of Al Qaeda's sources of financing, which could create diplomatic problems for the United States if his information points to prominent figures in Saudi Arabia and elsewhere.
Despite the arrest, the threat posed by Bin Laden's organization remains high, counter-terrorism officials said Saturday. Al Qaeda has always been an alliance of movements with a limited hierarchy, not a regimented force comparable to paramilitary terrorist groups or crime cartels. The network's structure has become increasingly decentralized since the U.S. invasion of Afghanistan.
"It is without question a big catch," said Bruguiere, the French judge. "But I do not think it will have an important effect on the menace.
"The networks are so dispersed that the arrest of one man, as significant as he is, does not change that much."
But other experts said remaining Al Qaeda leaders might not have his determination, experience and flair, and the arrest of Mohammed could make it harder for the network to pull off sophisticated, large-scale attacks using chemical and biological weapons or radioactive dirty bombs.
And even a weakened Al Qaeda has succeeded in creating a climate of fear in which a smaller, more traditional strike in Europe or the U.S. would have disproportionate impact.
"This is essentially psychological warfare," said Stefano Dambruoso, one of Italy's top anti-terrorism prosecutors. "Today, a small attack would be enough to create a disproportionately large reaction."
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The most-wanted list
Some of the major Al Qaeda figures still sought by authorities:
Osama bin Laden: Saudi, supreme leader. On FBI's
Ayman Zawahiri: Egyptian, Bin Laden's doctor, spiritual advisor. On FBI's most-wanted list.
Saif Adel: Egyptian, Bin Laden's security chief.
Mustafa Ahmad: Egyptian, Bin Laden's chief financier.
Tawfiq Attash Khallad: Yemeni, operational leader, suspected mastermind of Cole bombing in October 2000.
Saad bin Laden: Saudi, Bin Laden's son.
Abu Musab Zarqawi: Jordanian, operational planner.
Sulaiman abu Ghaith: Kuwaiti, Al Qaeda spokesman.
Mohammed Jamal Khalifa: Saudi, Bin Laden's brother-in-law
and terrorist financier.
Source: Associated Press