Hamburg investigators said Mohamed Atta, 33, and Marwan Alshehhi, 23, had studied at the Technical University in Hamburg and were from the United Arab Emirates. Both men received pilot training at Huffman Aviation, a flight school in Venice, Fla., where FBI investigators are examining student records.

Atta and Alshehhi also took two three-hour courses at SimCenter Inc. in Opa-locka, said Brian George, son of flight school owner Henry George.

''We were completely stunned and shocked,'' Brian George said. ''My father said that if he didn't have a family to support he would stop teaching tomorrow. To think that someone would take what he taught them and turn it into a weapon.''

Both men trained on a Boeing 727 full-motion simulator, he said.

Federal agents in Florida also were investigating at least three other men Thursday after searching homes and rental car documents and poring over flight school student records across the state.

The FBI issued a bulletin for authorities to look out for a silver 1996 Chrysler Plymouth and its possible driver Amer Kamfar, a flight engineer who listed a Saudi Airlines post office box as his address in FAA records and lived in Vero Beach, about 70 miles north of West Palm Beach.

Agents were questioning Saudi flight engineer Adnan Bukhari, 41, whom a county sheriff's official said was cooperating with FBI inquiries. Bukhari was a student at Flight Safety, which trains commercial jet crews.

Neighbor Wendy Harp said her 12-year-old daughter often played with Bukhari's children and she called a sheriff's investigator Thursday because she was concerned about her family's safety.

''He said Bukhari was being very cooperative and at this time he didn't feel there was any reason to believe that he was directly involved,'' Harp said. ''It looks like he had an association with someone else who was involved.''

FBI officials in Washington and Miami would not comment Thursday.

Agents searched four Vero Beach homes, including Bukhari's and the house next door, where another Flight Safety student, Abdulrahman Alomari, lived with his wife and four children.

Bukhari's brother, Ameer Bukhari, was a student pilot at Flight Safety Academy when he was killed in a mid-air collision exactly a year before Tuesday's attack.

Kamfar, 41, was listed as living at the same address as Alomari at different times. He previously was issued a driver's license in Venice, Calif.

Landlord Lonny Mixel said Thursday that Alomari arrived in July 2000 and told him he was a commercial pilot from Saudi Arabia and was in Vero Beach to attend Flight Safety Academy. Alomari said he would be out of the house by the end of August. Then he pushed the date back until Sept. 3 and moved out that day.

''He said he was going back home,'' Mixel said.

FBI agents were also interviewing three Saudi flight engineers who are taking classes at Flight Safety Academy, company spokesman Roger Ritchie said Thursday. He declined to identify the students.

The school does not have simulators for Boeing 767 and 757 aircraft such as the ones involved in Tuesday's attacks, Ritchie said.

Thomas Quinn, a New York-based spokesman for Saudi Arabian Airlines, said many of the airline's pilots came to the United States for flight training. Foreign students must be sponsored by an airline to attend Flight Safety.

FBI agents also sought information on a graduate of Embry-Riddle Aeronautical University in Daytona Beach, The News-Journal of Daytona Beach reported.

Citing two unidentified law enforcement sources, the newspaper reported that Waleed Al Shehri, 25, was listed as a passenger on the American Airlines flight that left Boston and crashed into the World Trade Center.

Al Shehri graduated from Embry-Riddle in 1997 with a bachelor's degree in aeronautical science, the university's commercial pilot training degree, and is listed as having a commercial pilot's license.

German investigators believe Atta and Alshehhi belonged to a terror group formed ''with the aim of carrying out serious crimes together with other Islamic fundamentalist groups abroad, to attack the United States in a spectacular way through the destruction of symbolic buildings,'' chief federal prosecutor Kay Nehm told a press conference in Karlsruhe.

There was no immediate link to Osama bin Laden, but they did have links to other terror cells abroad, Nehm said.

In Pompano Beach, FBI agents went Wednesday night to Warrick's Rent-A-Car to confiscate rental contracts, receipts and Visa credit card charge slips on a series of three rentals by Atta beginning Aug. 6, owner Brad Warrick said Thursday.

Alshehhi on Sunday turned in a car rented by Atta, Warrick said. The FBI was at the agency Thursday to impound a second car that Atta rented last month, he said.

''He appeared to me to be just a very conscientious, nice businessman,'' Warrick said. ''I'm really just a little small, hole-in-the-wall rental office ... We're an inconspicuous place to go.''