Authorities piecing together the events leading up to the Sept. 11 terrorist attacks have learned that the Justice Department denied an FBI request to examine the computer of a man now believed to have been involved in the deadly hijackings.

Law enforcement officials revealed Tuesday that FBI agents wanted to search the computer of Zacarias Moussaoui, who is currently being held and questioned as a material witness.

Instead, the computer was scrutinized after the attacks and found to have data stored that was related to commercial jets and crop-duster planes — the latter of which have been temporarily grounded out of fear of a possible chemical terrorist assault.

The Department of Justice turned down the FBI request for a search warrant because authorities didn't have enough evidence to obtain one under the Foreign Intelligence Surveillance Act, according to a law enforcement official who spoke on condition of anonymity.

The source said that Moussaoui, a French-Algerian, isn't cooperating with investigators. He was detained Aug. 17 after he acted suspiciously at a Minnesota flight school and was subsequently sent to New York, where a grand jury is conducting a probe into the disaster.

Moussaoui apparently told instructors at the school that he wanted to learn to fly a jetliner but didn't want to learn to land. He also asked about opening cabin doors while planes were in flight. His behavior raised eyebrows, causing the flight school to contact the FBI.

Taken into custody on suspicion of immigration violations, Moussaoui was behind bars when his alleged colleagues hijacked four jetliners and crashed them into the World Trade Center, the Pentagon and a field in southwestern Pennsylvania.

Newsweek magazine first reported the FBI's request for a search warrant and the Justice Department's rejection.

Police officials say France's internal security service had placed Moussaoui on a 1999 watch list of those possibly affiliated with militant Islamic groups.

Details about Moussaoui emerged as Attorney General John Ashcroft said U.S. officials have told American allies that some of the same terrorists involved in the Sept. 11 attacks also have been linked to the East Africa embassy bombings and the bombing attack on the USS Cole.

The links, contained in a detailed summary of evidence sent to allies Monday, connect the hijackers to fugitive Saudi millionaire Usama bin Laden, who has been indicted in the embassy bombings and is thought by U.S. officials to have masterminded the Cole attack.

Ashcroft refused to detail evidence but said, "The roots of these activities were in Afghanistan.

"From very early stages in the investigation, we saw Usama bin Laden, the Al Qaeda network, as being a focal point of those responsible for this act of terror," said Ashcroft.

He also said that because of the risk that terrorists could slip across the Canadian border into the United States, the two are working together to tighten security.

"Any time there are borders that are that open, and that substantial, there are risks," Ashcroft said in an appearance with Canadian Solicitor General Lawrence MacAulay, who has been appointed to a Cabinet-level commission to combat terrorism in Canada.

Ashcroft's pledge for tighter border security came as documents showed that one person in custody as part of the terrorism investigation entered the country through Canada a few weeks before the attacks.

Immigration papers released by the Justice Department showed authorities were holding a Pakistani who entered the country illegally across the Canadian border about two weeks before the hijackings. The individual, who tried to enter the country at Massena, N.Y., has been detained since Aug. 30, the documents said.

Another Pakistani entered the country through Miami using a fake passport and visa last April, the documents showed.

The names of those detained are blacked out for privacy reasons and the documents do not specify whether the detainees are linked to the hijackings. Immigration authorities have detained 142 people in connection with the terrorism investigation.

In other developments:

• The government is investigating trading in shares of 38 companies, including major airlines, cruise lines, General Motors and Raytheon, to determine whether people used advance knowledge of the terror attacks to profit.

• Five gasoline stations in Sullivan County, N.Y., were raided by federal agents, who questioned some of the managers about the September attacks and in some instances seized the businesses' financial records. Two gas station proprietors said the agents were from the Internal Revenue Service.

Gas station manager Manhar Patel said the agents asked about the attacks of Sept. 11, and that when they mentioned the World Trade Center, "I told them I knew nothing about that."

The Associated Press contributed to this report.