The FBI is continuing a nationwide manhunt for more than 200 people it believes may have ties to the hijackers. As many as 30 of the people on the bureau's "watch list" are believed to have had flight training.
ABCNEWS has learned that some of the men believed to have been trained as pilots had booked reservations on airline flights scheduled to take place in the days after last week's attacks — including flights coming out of Boston and San Antonio this coming weekend.
As he surveyed the Western Pennsylvania crash site, Attorney General John Ashcroft vowed to "disrupt, interrupt, stop, thwart, curtail the risk of further events like those events of Tuesday, September 11."
The attorney general said a day earlier he could not rule out that additional aircraft had been targeted for hijackings.
"We will leave no stone unturned to make sure that we do what we can to minimize the risk of reoccurrence," Ashcroft told reporters this afternoon.
Law enforcement officials said they believe the operations of the hijackers were based in Florida, Texas and New Jersey.
Many of the 30 or so individuals thought to have had pilot training are also known to have communicated with the hijackers.They are from a variety of locations within the United States and all of them are believed to still be in the country.
"This long list of people who had some kind of contact with the suicide hijackers of Sept. 11 … They may be part of a network," says ABCNEWS security consultant Vince Cannistraro. "That is a concern that is driving law enforcement in the investigation."
The FBI has obtained cell phone records and hundreds of e-mail messages exchanged by many of the 19 hijackers and their associates in the days and weeks leading up to the attacks.
• New Arrest Made
More than 115 people are now in federal custody in connection with the investigation, including several individuals who have been placed under arrest.
Most recently, a man identified as Nabil al Marabh was arrested Wednesday night at a liquor store where he worked the late shift in Burbank, Ill., just outside Chicago. Al Marabh had a commercial driver's license that allowed him to transport hazardous materials.
Sources tell ABCNEWS investigators believe al Marabh has ties to at least two of the suspected hijackers and the U.S.Customs Service has linked money transfers from Marabh to Raed Hijazi, a suspect in a failed plot to kill American tourists in Jordan during the 2000 millennium celebration.
Marabh, who has been in the United States for 11 years, sometimes working as a cab driver, has lived all over the country, including Tampa, Boston and Michigan. Marabh was convicted of stabbing his roommate in Boston and according to court records allegedly said, "If this wasn't America, I'd kill you."
When agents searched al Marabh's apartment in Detroit earlier this week, they found notes relating to an airport in Jordan, a diagram of an airport and fake identification badges.
Three Arab men were taken into custody at the residence and have been formally charged with the possession of false identification documents.