The most dangerous men in America found the perfect refuge as they secretly rehearsed plans to carry out the deadliest terror attack in US history. They rented homes in the heart of suburban Florida with their wives and children. No one suspected a thing - until last Tuesday morning. By then, it was too late.
Now, in the wake of the suicide assaults on the World Trade Center and the Pentagon, some 4,000 federal investigators are fanning out across the country to track down thousands of leads, while working to preserve and analyze every scrap of potential evidence.
From passenger lists and airport security cameras, to cockpit voice recorders and tiny pieces of cloth and metal in the mountain of debris at the World Trade Center, investigators say they are leaving no potential clue unexamined.
It is being called the most comprehensive criminal investigation ever undertaken. And the stakes are extremely high.
Federal agents must quickly determine whether there might be other secret cells of terrorists in the US, or remnants of the former cells, that are preparing to carry out similar terror attacks.
Moreover, they are working to identify the mastermind of the Sept. 11 terror plot and anyone who supplied the hijackers with financial or logistical support. The hope is to establish an investigative trail that implicates terrorist leaders overseas and the foreign governments that support or protect them.
President Bush and Secretary of State Colin Powell have targeted exiled Saudi millionaire Osama bin Laden as the prime suspect behind the recent attacks. "If he thinks he can hide and run from the United States and our allies, he will be sorely mistaken," Mr. Bush says.
But terrorism experts say building a solid legal case against Mr. bin Laden may prove difficult. "Under American law, to trace this to Osama bin Laden, you need a whole bunch of people saying that they got orders from him, and we may not be able to trace that kind of thing," says Richard Hrair Dekmejian, a political science professor at the University of Southern California in Los Angeles and author of "Islam in Revolution."
He says alleged bin Laden associates arrested in the past have refused to cooperate with US investigators. He adds that it may be hard to prove that bin Laden's political and religious activities played a direct and criminal role in a particular terror attack.
"Osama bin Laden has inspired many people and told many people to engage in jihad [holy war], but did he organize and fund all this?" Mr. Dekmejian asks. "It could be difficult to prove unless some of these people point a finger at him."
But military action against bin Laden seems much more likely than the prospect that he would be seized and returned to the US to stand trial, says Richard Bulliet, a history professor and director of the Middle East Institute at Columbia University in New York. "I think there is a distinction between terrorist acts that fall in the category of criminal activity and those that fall in the category of warlike activity," he says.
From this perspective, the current investigation is much more important to the US for the intelligence it could provide US forces.
Besides the 19 hijackers identified by the FBI, US immigration agents are detaining at least 25 individuals believed to have information about the hijackers. Government officials say some of the detainees are cooperating with the FBI, but the officials decline to quantify the extent of that cooperation.
In addition, agents are working to trace all transactions associated with the hijackers. The basic investigation began with passenger lists obtained from the airlines. "They started with aircraft manifests. That led quite rapidly to the identification of the members of the group that actually went on board the aircraft," says Peter Crooks, a former FBI counterterrorism specialist who is now a professor at Southern Connecticut State University in New Haven. "That gives you a focal point to start moving out."
From there, investigators identified cars rented by the group, and computers and cellphones they used. Documents related to the equipment indicated home addresses and businesses, Mr. Crooks says. From there, agents were able to question neighbors and colleagues.
One particularly critical question is how the hijackers were financed. Credit cards were used for some purchases, and others were paid in cash. But experts say that given the degree of organization, the hijackers' finances were almost certainly laundered to prevent any tracing.
"My guess is that the money trail will lead to the [Arabian] peninsula and disappear in the sands," says Mr. Bulliet.
Yet the investigation is painting a surprisingly detailed portrait of the group of men who allegedly conspired to hijack four commercial jets. At least half of the 19 men identified by the FBI as hijackers are believed to have been natives of Saudi Arabia. The others appear to have come from neighboring countries.
They came to the US apparently as committed members of a terror organization and undertook additional flight training needed to carry out their attacks, terrorism experts say. Several of the men registered at flight schools to learn how to pilot various types of aircraft.
They were well supplied with money, but did not flaunt it in a way that might attract attention. And if they communicated with group leaders outside the US, they apparently did so without being detected by US and other allied intelligence services. Discovering how they may have avoided such detection will be an important part of the investigation, experts say.