"This long list of people who had some kind of contact with the suicide hijackers … 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.
"We will not sleep until they are brought to justice," FBI Director Bob Mueller vowed today as he and Ashcroft toured the damage in New York.
"We will bring them to justice or if that's impossible, we will take justice to them," the attorney general added, paraphrasing a line from the president's address to a joint session of Congress Thursday night.
Investigation's Midwest Focus
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.
Sources tell ABCNEWS investigators believe Al-Marabh, 34, has ties to at least two of the suspected hijackers and the U.S. Customs Service has linked money transfers from Al-Marabh to Raed Hijazi, a suspect in a failed plot to kill American tourists in Jordan during the 2000 millennium celebration.
Al-Marabh, who had a commercial driver's license that allowed him to transport hazardous materials, has lived all over the United States for the last 11 years, including in Tampa, Boston and Michigan.
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 that residence and have been formally charged with the possession of false identification documents.
Meanwhile, a man who has been held by Canadian authorities since shortly after the attacks was charged today in Chicago with two counts of intent to use a false passport. The man, who used the name Najib Mohammed, was on a flight from Germany to Chicago on Sept. 11 when it was diverted to Toronto after U.S. airports were closed.
Canadian authorities became suspicious because they said Mohammed has three different passports. In adddition, his luggage had arrived in Chicago on an earlier flight, and because it was unclaimed, customs agents opened it and found Lufthansa Airlines crew uniforms and "suspicious" writing on a paper sewn into a pants pocket.
However, Canadian officials said they had found nothing linking Mohammed to the suspected hijackers. The FBI is seeking his extradition to the United States.
In New York, an investigation by a grand jury in White Plains has led to the detention of some 75 people for questioning, with five people under arrest as material witnesses. Among those arrested is an alleged associate of bin Laden, who was taken into custody Aug. 17 after workers at a Minnesota flight school raised suspicions about him.
There is now some confusion among law enforcement officials about the real identities of the 19 men pegged by investigators as the terrorists who hijacked the four planes on Sept. 11. Mueller acknowledged Thursday that some of the hijackers may have been traveling under aliases and stolen names, and that the identities of "several" of them are "still in question."