Only one man, say counterterrorism experts, had the motive - and capability - to carry out terrorist attacks of this magnitude: Osama bin Laden.
"From the scale and obvious coordination, it seems clear that a major group is responsible - and like most people, I'm betting on Osama bin Laden," says a former analyst who worked in the CIA's counterterrorism unit. "The fact that he signaled a major hit three weeks ago suggests his organization is responsible."
Stanley Bedlington, a retired CIA officer who also worked in counterterrorism, agrees: "What really points to Osama bin Laden is the similarity to the attacks in Nairobi, Kenya, and Dar es Salaam, Tanzania, in 1998," says Mr. Bedlington. "There are some direct correspondences - the fact that two attacks in two different countries were carried out at the same time which resulted in enormous casualties, and now there are these attacks in New York and Washington which occurred within an hour."
There are other groups, of course, who could be responsible. There are many groups in the Mideast angry with the US over its Israel policies, says Bedlington. And he points to the mass demonstrations at the recent World Bank meeting in Washington. Most of the demonstrators were peaceful, he points out. But "there are groups committed to violence - both anti-capitalist and anti-military. The question is though, whether they have the capabilities or resources. They probably have the resolve, but that's it."
The logic behind this thinking, and that of other experts in this area, is that to carry out the massive attacks that were leveled against American targets yesterday, a great deal of organizational skills, planning, and resources went into the operation.
The people who perpetrated these attacks must have been in the US for some time, planning and waiting - most likely in East Coast cities, since that's where most of the attacks were initiated. And most likely there were several people involved - enough people in each crew to subdue a flight crew, the cabin, and someone who knew how to either direct the pilot with the coordinates for the targets or who flew the plane into the targeted buildings himself.
These people would have been set up in "safe houses," where they were waiting for the right moment. They would have had to scope out the airports' security, the flight patterns, and gather the weapons to carry on the plane - most likely undetectable plastic guns that were broken down and then assembled in flight.
"They were seeded here and waiting," says the former CIA counterterrorism specialist. "It looks so far that the planes came from the East Coast and were loaded with jet fuel - setting out for long-distance flights. So they were clearly targeted as planes full of fuel, which are more explosive."
She goes on to say that these people would have had to come into the US early enough to get through border controls. When bin Laden issued his alert three weeks ago, the US government would have clamped down on the borders. But the terrorists would have been already here. For example, Mir Amail Kanzi, who attacked the CIA in 1993, killing two and wounding three, had been in Arlington for over a year waiting to perpetrate the attack, she points out.
That kind of capability only points to bin Laden's group, Al-Qaeda, these experts say.
"The Al-Qaeda is an umbrella group that is affiliated with a number of terrorist organizations throughout the Middle East - from Egypt to Kashmir and into Pakistan," Bedlington says. "It has networks, including offices, in Europe and fund-raising capabilities in the US."
Officials of the Taliban government in Afghanistan, where bin Laden has lived in hiding since 1996, denied that the Saudi dissident had played a role in the terrorist attacks. "Osama is only a person. He does not have the facilities to carry out such activities," said Abdul Salam Zaeef, the Taliban's ambassador to Pakistan. "We want to tell the American people that Afghanistan feels their pain."
But in the past month bin Laden was appointed "Inspector General" of the Taliban militia, according to Grigory Bondarevsky, an expert on Afghanistan who advised the Russian military in the 1980s, and still keeps close contacts.
Bin Laden was once a revered member of Afghanistan's Islamic mujahideen resistance against the Soviets in the 1980s - trained by the CIA, and so effective as a recruiter that close comrades at the time actually thought he was working for the CIA.
Bin Laden once called the death of 18 American servicemen in Somalia in October 1993 his "biggest victory." But while no evidence ever surfaced that he was linked to that battle, the bombing of the US Embassies in Kenya and Tanzania in August 1998 - which left 224 dead and 4,000 wounded, and was traced back to bin Laden operatives - showed how deadly precise the al-Qaeda organization could be.
Western intelligence officials now reportedly also believe that the suicide bombing against the USS Cole in Yemen, which left 17 American sailors dead, is the work of bin Laden agents.
"The victory of Yemen will continue," bin Laden said earlier this year, another warning in a tape that surfaced in June, that US intelligence officials apparently believe lays out bin Laden's plans for further attacks, according to the New York Times.
Apart from the Arab-Israeli conflict, bin Laden's constant complaint about US policy has been the presence of as many as 20,000 American troops deployed in the Persian Gulf. Bin Laden routinely calls these troops "infidels" in the Islamic holy land.