The FBI found transactions that show Atta used a credit card in Manhattan the day before the planes crashed into the World Trade Center. Until recently, law enforcement officials could not figure out why he was here.
New evidence has emerged that leads investigators to believe Atta made a last-minute visit to double-check coordinates of the twin towers and plug them into a sophisticated Global Positioning System device bought by the hijackers, the source said.
Investigators suspect Atta's trip to the Trade Center was necessary because they believe the hijackers were too inexperienced to handle the jumbo jets without help. They know the hijackers bought GPS devices in the months leading up to the attack.
The FBI's New York office declined to comment on what the bureau knows about Atta's final hours.
The unusual flight paths of American Airlines Flight 11 and United Airlines Flight 175 — which traveled from Boston and into the twin towers — indicates the hijackers used the devices to guide them as they flew across the country toward what was about to become known as Ground Zero, the source said.
Federal prosecutors say that on Aug. 25 — three weeks before the attack — one of Atta's co-conspirators, hijacker Ziad Jarrah, bought GPS components.
Flying Equipment Bought
Atta himself bought flight deck videos for jumbo jets and several unnamed items from Sporty's Pilot Shop in Ohio in November 2000. Sporty's owners said FBI agents investigating the Sept. 11 attacks asked about a Garmin GPS III Pilot, a hand-held device that simplifies aeronautical navigation.
And Zacarias Moussaoui, the so-called 20th hijacker now indicted on terrorism charges in the Sept. 11 plot, also tried to buy a GPS receiver, prosecutors have said.
With the coordinates of the twin towers entered as the desired destination, the devices would tell the hijackers when they were off course as they flew thousands of feet above the ground.
Experts noted that the hijackers could have obtained coordinates of the towers from available maps, but visiting the site with the device would ensure that the specific data were pinpoint accurate.
It's not clear how long Atta was in Manhattan before the attack. The source would not discuss the credit card transactions here except to say they took place in Manhattan.
Sometime on Sept. 10, the FBI believes, Atta traveled to Boston and rented a blue Nissan sedan. He and Abdulaziz Alomari then drove to Portland, Maine.
Seen on Video
They checked into a Comfort Inn in South Portland at 5:43 p.m., then visited two bank ATMs and a Wal-Mart, where they were captured on video.
The morning of Sept. 11, they checked out of the motel at 5:33 a.m., arriving at Portland International Jetport in time for a last-minute boarding of a 5:45 a.m. flight to Boston.
They arrived at Boston's Logan Airport just in time to board American Airlines Flight 11, departing at 7:55 a.m., fully fueled, with a scheduled destination of Los Angeles.
Sometime during the flight — as the plane headed west over upstate New York — the FBI believes Atta, Alomari and three others hijacked the jet and turned it south — toward the towers of New York.
