Filed at 11:59 a.m. ET

BOSTON (AP) -- Logan International Airport officials defended their security system as investigators started tracking the hijackers who boarded two airliners at the airport and crashed them into New York's World Trade Center towers.

Their commments came even as the Federal Aviation Administration said it did not know when it would allow commercial air traffic to resume over the United States.

Two suspects flew to Boston from Portland, Maine, the governor of Maine said Wednesday. The Boston Herald quoted a source as saying five Arab men had been identified as suspects, including a trained pilot.

Authorities said they received no unusual communications from American Flight 11, which left Boston at 7:59 a.m. Tuesday with 92 people aboard, or from United Flight 175, which took off 15 minutes later, with 65 people.

The 767s, both bound for Los Angeles, sliced into the twin towers 18 minutes apart.

``Everything seemed normal when they left Logan,'' said Joseph Lawless, public safety director of the Massachusetts Port Authority. ``We don't know how the hijackers accomplished what they did.''

``We have a very high security standard here,'' Lawless said. ``We consider ourselves as secure, if not more secure, than any other airport in the United States.''

Maine Gov. Angus King said two suspects had flown to Boston from the Portland International Jetport, and left behind a rental car that was impounded in the Portland area. King, who was brief by state police, said the men apparently used New Jersey driver licenses but little else was known about them.

``This information appears to open up a series of leads that I'm sure will help to identify who the attackers,'' King told The Associated Press.

The FBI chief in Maine, Jim Osterrieder, declined to comment on the report.

The car, a blue Nissan Altima, was identified at 11:30 p.m., Portland Police Chief Michael Chitwood said. Cigarette butts found next to the car will be tested for DNA, and the car was taken to a crime lab, Chitwood said.

Another rental car, containing Arabic-language flight training manuals, was seized in a Logan parking garage, The Boston Herald said Wednesday, quoting an anonymous source. The source said five Arab men had been identified as suspects, including one who was a trained pilot.

Authorities were led to the car by a traveler who said he got into an argument with several men as they were parking their car, the Herald reported. The traveler, who said the men appeared to be Arabs, called state police after learning the planes were hijacked from Logan, the newspaper said. It did not identify the traveler.

The Herald said two suspects flew to Logan on Tuesday from Portland, Maine. Authorities believe the two had entered the country recently from Canada, the newspaper said. Two of the men, including the trained pilot, were brothers with passports traced to the United Arab Emirates, the Herald reported.

The Boston Globe reported one suspect's luggage did not make the connection. The bag contained a copy of the Quran, an instructional video on flying commercial airliners and a fuel consumption calculator, the newspaper said.

WCVB-TV in Boston reported the car seized at the airport had Virginia license plates. The station also said six bags of evidence were taken from the airport to the Boston FBI office, including chairs the suspects may have used while waiting to board the flights.

The FBI in Boston refused to comment on the reports.

The airport was evacuated and remained closed Wednesday.

``Clearly, there were two failures of security at Logan Airport,'' said Sen. John F. Kerry. ``It's not just Logan. If you have four hijackings in one day, you have a national problem.''

Hijackers also crashed a plane out of Dulles International Airport near Washington into the Pentagon and another hijacked commercial flight from Newark, N.J., was crashed southeast of Pittsburgh.

Port authority officials said they planned security measures at least as stringent as those last implemented during the Persian Gulf War, including allowing only passengers past security checkpoints and eliminating curbside check-ins.

``One could speculate ... why we were chosen was because of our proximity to the New York area and the fact that we have wide-bodied aircraft leaving our airports fully loaded with fuel that participated in this tragic kamikaze-type attack,'' Port Authority aviation director Thomas Kinton said.

Lawless said Globe Aviation Services Corp. of Irving, Texas, and Huntleigh USA Corp. of St. Louis operate security checkpoints for American and United flights at Logan. People who answered the telephone at both companies' headquarters refused to comment.

In 1999, the major airlines at Logan and the Port Authority were fined a total of $178,000 for at least 136 security violations over the previous two years. In the majority of incidents, screeners hired by the airlines for checkpoints in terminals routinely failed to detect test items, such as pipe bombs and guns.

Also in 1999, a teen-ager who said he wanted to impress the Israeli intelligence agency allegedly sliced through a fence and settled into an empty seat on a British Airways jet and flew to London.