The Washington Post and the associated press

Federal authorities have identified more than a dozen hijackers in Tuesday’s bombings and gathered evidence linking them to Osama bin Laden and other terrorist networks, law enforcement officials said.

Terrorists succeeded in flying two hijacked airliners into the 110-story World Trade Center towers in New York and a third into the Pentagon in Washington, D.C., on Tuesday. A fourth crashed near Pittsburgh after passengers apparently mounted a revolt, according to accounts of cell-phone conversations.

Thousands of FBI agents fanned out across the country Wednesday in the hunt for accomplices to the terrorist attacks on New York and Washington, executing search warrants from Boston to Florida and detaining at least four individuals believed to have ties to the hijackers.

The massive investigation stretched from the Canadian border, where officials suspect some of the hijackers entered the country, to Florida, where some of the participants are believed to have learned how to fly commercial jetliners before the attacks. Locations in Massachusetts and Florida were searched for evidence.

Using airplane manifests, passport records and other sources, U.S. officials believe they have successfully identified most of the suicidal hijackers, who numbered possibly as many as 50 individuals and included several pilots who received flight training in the United States, according to Attorney General John Ashcroft, FBI director Robert Mueller and other officials.

"The four planes were highjacked by between three and six individuals per plane, using knives and box cutters and, in some cases, making bomb threats," Ashcroft said.

At least one hijacker on each plane received flight training in the United States, Justice Department spokeswoman Mindy Tucker said Wednesday night. She said flight schools in several states were part of the FBI’s investigation.

The FBI detained a man for questioning and served search warrants on at least four separate locations in Florida, while heavily armed federal agents detained three people at a hotel in downtown Boston after law enforcement officials traced credit-card receipts from a car rental agency to a guest there. Law enforcement officers also searched a hotel in Newton, outside Boston.

Ashcroft, who briefed members of Congress on the investigation, said investigators were obtaining passenger manifests, rental-car receipts, telephone logs, and videotapes from parking garages and pay phones, particularly in the places of origin for the hijacked flights.

Canadian security officials are also investigating whether as many as five participants in the deadly attack used Canada as a staging ground, slipping across the border from Nova Scotia shortly before the hijackings. Two of the hijacked planes took off from Logan International Airport in Boston; the others were from Newark International Airport and Washington’s Dulles International Airport.

Those detained in the United States as of late Wednesday afternoon were being held on immigration violations but had not been arrested or charged with any crime, according to Mueller and others.

Ashcroft also said the "government has credible evidence that the White House and Air Force One were targets" of the terrorists

"We will leave no stone unturned until we have determined who was responsible for these attacks on our freedom," said Mueller, who is in his second week on the job.

Mueller said some of the suspected hijackers and their accomplices had ties to several terrorist groups, but he declined to provide details.

But other U.S. officials said several of the groups are known to have ties to Saudi fugitive Osama bin Laden, an extremist Islamic militant. His organization, Al Qaida, has been linked to numerous terrorist bombings, including a previous attack on the World Trade Center in 1993 and the bombings of U.S. embassies in Kenya and Tanzania in 1998.

After a briefing Wednesday by intelligence officials, Sen. Kay Bailey Hutchison, R-Texas, a member of the Armed Services Committee, said authorities have discerned a "pattern of travel" by about 15 individuals, including five who have been found to be carrying passports from two Middle Eastern countries. She did not identify the countries.

Hutchison said the 15 were found to have gone to one or more other countries before entering the United States. Canada was not specifically mentioned, she added.

Asked about bin Laden’s possible connection to the attacks, she said, "He is certainly high on the list … but he is not the only one they’re looking at."

In Florida, search warrants were served on homes in Coral Springs, west of Fort Lauderdale, on a home in Vero Beach along Florida’s east coast, and on businesses in Hollywood and a home in Sarasota County on the West Coast, according to police and witness reports.

Aschcroft’s statement that some of the pilots who carried out Tuesday’s hijackings were schooled in the United States provides further evidence that the terrorists had the training necessary to carry out the precision attacks.

Officials said many of Wednesday’s searches and detentions were prompted by a review of the passenger manifests of the four hijacked planes.

In Vero Beach, FBI agents detained a Saudi Arabian pilot who had received flight engineering training, along with at least one other Saudi at the local Flight Safety Aviation School, according to the home’s property owner. Among the items seized by the FBI was a "hazardous materials manual," according to a copy of an FBI document left on the home’s kitchen table.

Landlord Paul Stimeling said the detained man, Adnan Bukhari, helped a second Saudi pilot rent the house next door. The second pilot and his family, including his wife and as many as five children, moved out over the weekend and haven’t been seen since, Stimeling said. Bukhari was also in the process of moving, he said.

Both of the men said they were Saudi nationals and flew for Saudi Airlines, Stimeling said. FBI agents swarmed the neighborhood Wednesday morning and spent several hours searching the homes, witnesses said.

The Immigration and Naturalization Service is investigating whether two of the hijacking suspects may have come into the country with "M" visas, a rarely issued nonimmigrant visa that allowed them to attend the Florida flight school, according to a former senior INS official who has talked to investigators. INS officials are also concerned that one or more of the suspects may have entered the United States while seeking asylum.

In Boston’s Copley Plaza, local police and agents from the FBI and the Bureau of Alcohol, Firearms and Tobacco descended on the Westin Copley Hotel with battering rams and shields, detaining three men who were tracked using a credit-card receipt from a car rental, officials said.

One man detained in Boston was recognized on news reports Wednesday by an Amtrak train attendant, who told the FBI that he recognized the suspect as having traveled from Florida to New York via train within the last few days, according to an Amtrak official.

Several hijackers may have entered the United States shortly before the attacks by taking a ferry from Nova Scotia to Portland, Maine, according to several sources.