U.S. government officials say they have not yet identified any groups or persons responsible for the terrorist attacks today, and experts say it could take a great deal of time and effort to determine who might have been involved.
But intelligence analysts suggest the apparently coordinated attacks — against the World Trade Center in New York, the Pentagon outside Washington, and the downing of a jet in Pennsylvania — have the mark of Osama bin Laden's network al Qaeda.
"You would think it would have to be bin Laden behind it, because who else would have the audacity, the conceptual audacity of it?" says John Pike of GlobalSecurity.org in Washington.
"His organization fits the profile. There are very few international terrorist organizations with such skill sets capable of launching such a massive and coordinated attack," says Stratfor analyst Jamie Etheridge in Austin, Texas.
"His organization incorporates the tactics used … suicide [attack], coordinated attack," she says. "They probably used trained pilots to ram the World Trade Center."
Sen. Orrin Hatch, R-Utah, ranking member of the Senate Judiciary Committee, told ABCNEWS that "top people at the CIA" told him "just about everything points in the direction of Osama bin Laden." Hatch also said U.S. officials had some data suggesting bin Laden associates were on at least one of the aircraft that crashed apparently was brought down today.
Steven Aftergood, an intelligence analyst with the Federation of American Scientists, earlier cautioned: "I would like to forgo guessing. I think the evidence should be collected and should speak for itself.
"I think what can be surmised is this was the work of an exceptionally well-organized and sophisticated group of people and they must have left footprints in one place or another," he adds. "This was not bin Laden operating out of his tent."
Secretary of Defense Donald Rumsfeld in a press briefing today declined to discuss at this time whether bin Laden is suspected.
Thousands of FBI agents are investigating, Their probe will include visits to Boston's Logan and Virginia's Dulles international airports, from which three of the four planes that crashed in apparent hijackings today originated. They will be dissecting passenger lists for clues as to who may have been responsible, and calling relatives of the people on the lists. Agents also are executing search warrants based on the flight manifests.
The New York field division is deploying its Evidence Response Team to the World Trade Center to gather evidence.
Created in 1998, al Qaeda is a loose umbrella association of radical groups and people believed to operate in dozens of countries around the world and suspected of association with previous attacks against U.S. interests, including the 1998 bombings of two U.S. embassies in Africa and the attack on the USS Cole in the Yemeni port of Aden last October.
Bin Laden and others allegedly associated with him were indicted in the embassy attacks.
Over the course of the year, the U.S. State Department has issued a number of alerts pointing to the possibility that agents of al Qaeda may be planning an attack against U.S. military or civilian targets.
A June 22 alert said the U.S. government had learned "that American citizens and interests abroad may be at increased risk of a terrorist action from extremist groups."