The result: Many South Florida residents don't even know their neighbors because of the lack of community roots, say sociologists.

Some experts point to an interesting irony in why the terrorists may have picked Florida.

While it's a state with plenty of ethnic groups - allowing the terrorists to blend in - it's also a state with a relatively small number of Arab-Americans and Muslims.

The people who may have been most suspicious of the terrorists and their plans would have been other Arabs, say experts.

“It's not hard to understand,” says Dr. Walid Phares, a terrorism expert and professor at Florida Atlantic University in Boca Raton.

“They would have drawn attention to themselves by other [law-abiding] Arabs. They would have been asked a lot of questions. If you're a terrorist, you want to minimize your risks.”

In other words, it would have been more difficult to plan their mission in places like Toledo and Dearborn, Mich., he added, where the concentrations of people of Middle Eastern descent is greater.

From the beginning, the terrorists seemed determined to conceal their identities and mission at all costs, experts say.

They were known as “sleeper agents” who came together, but kept a low profile until they were called to duty.

Some are believed to have used stolen IDs or aliases along a twisted and confusing trail through cities like Vero Beach, Delray Beach, Hollywood, Coral Springs, and Deerfield Beach.

The city that attracted most of the suspects: Delray Beach, a quaint coastal community in Palm Beach County with a diverse population that was designated an All-American City this year and in 1993.

Maria Siscar-Simpson was stunned to learn that two of the suspects, Saeed Alghamdi and Ahmed Alnami, who were on the United Airlines Flight 93 that crashed in rural Pennsylvania, lived below her at the Delray Racquet Club.

“They looked like kids,” she told reporters. “Everyone thought they were tennis students. Honestly, they blended right in.”

She and others were surprised to discover that a New York firefighter missing in the World Trade Center collapse, Lawrence Stack, owned a condo directly across the street from the suspects.

“It's balcony to balcony. It's about 300 feet from terrorists to hero,” said local resident Ann Nathanson.

The terrorists' trail in Florida may have originated with the arrival of two suspects in May, 2000, with one moving to Delray Beach, the other to Daytona Beach, some 175 miles north.

The suspected ringleader, Mohamed Atta, arrived in July, 2000 - just days after he visited a flight school in Oklahoma, according to interviews and records. He ended up in Florida instead.

Described by people who knew him as a reedy and serious 33-year-old urban planner, he and fellow terrorist Marwan Al-Shehhi showed up at the Huffman Aviation flight school in Venice.

Atta, who was born in Egypt, wrote a check for $10,000 to begin training at the flying center.

For the next five months, the two men quietly took lessons, initially staying at the home of an instructor for $37 a night, and later, renting an apartment.

While they kept to themselves, Atta managed to make an impression on the owner of the flight school. “[He] was an arrogant son of a bitch,” Rudi Dekkers told the St. Petersburg Times.

The dark-haired, 5-foot-8-inch-tall leader drove a red Pontiac, used his cell phone frequently, and dressed in the latest fashions, recalled another student with no ties to the terrorists, Ali Azzan.

The two suspects' political leanings were obvious, said Mr. Azzan. “They liked to discuss politics, often railing about Israel,” he said.

By the time America's attention was focused on Florida during the now infamous presidential recount in December, the two men were qualified to fly small, multi-engine planes.

That same month, at least 12 of the other conspirators were in Florida, moving from motels to rental units to condos, records show. Some may have taken flight lessons as early as 1993 in Florida.

Between January and March of this year, Hamza Alghamdi and Mohand Alsheri - both on the United Airlines Flight 175 that crashed into the World Trade Center - plunked down $200 to rent a mailbox at a Delray Beach shopping center.

It was the first in a series of mail drops and bogus addresses the killers-in-waiting used to obtain driver's licenses and reserve plane tickets.

One expert believes the terrorists moved from place to place for obvious reasons.

“They wanted to stay ahead of anyone who may have been trailing them,” says Don Pierce, a former federal task force agent in Delray Beach.

“If you just keep moving, you can stay ahead of people. These are people that are probably not going to draw a lot of attention anyway.”

According to news accounts and interviews, Atta moved to at least three places in the 14 months he lived in Florida.

At times, he and others rolled out wads of cash - $100 and $50 bills, witnesses have said. But in South Florida, that's not going to raise eyebrows, says Dr. John Nutter, a former Michigan State University researcher who advises law enforcement agencies on terrorism.

With the numbers of wealthy people who flock there, “not having any visible means of support is fairly typical,” says Dr. Nutter. “They could have been wealthy heirs of oil money.”

Even when Atta and other conspirators visited the remote farming area of Belle Glade six months ago - about 40 miles west of Palm Beach - no one seemed to suspect anything.

Amidst the cane fields and sugar refineries, Atta went to the local airport to ask about crop-duster planes.

“He wanted to know how to fly it, how to crank it, how much it would haul,” recalled James Lester, 50, who services the crafts. Experts have frequently cited crop dusters as a possible means of dispersing dangerous chemical or biological agents.

Mr. Lester said Atta, believed to have crashed American Airlines Flight 11 into the World Trade Center, returned to the air strip as recently as August - a month before the attacks.

“It just amazes me now,” said Mr. Lester, who recognized Atta from a photo shown to him by an FBI agent.

By summer, the men settled into several spots, possibly awaiting orders, experts speculate. But all along, they continued to try to confound anyone who may have trailed them.

“You have to put yourself into the mind of a terrorist if you really want to understand these people. They did everything - everything - for a reason,” said Dr. Phares, the Florida Atlantic University professor who has testified before Senate subcommittees on Middle East conflicts.

He firmly believes the terrorists were aware that federal agencies in South Florida are more attuned to Latin and South American terrorists.

“This is not an area that concerns itself with Middle East terrorism,” said Dr. Phares, a native of Lebanon. “Speaking Arabic in public is not going to turn heads in Florida, but speaking in Spanish about people like Castro most certainly will.”

By spring of this year, a paper trail emerged: Al-Shehhi obtained his driver's license April 12, while Ziad Jarrah and Atta received theirs May 2.

A suspect who used the name Waleed Al-Shehri got his license May 4. Three more obtained licenses in July, reports show.

By summer, they joined local gyms and began visiting the Delray Beach public library.

Librarian Kathleen Hensman recognized several of their photos because they had frequented the downtown library to use the computers. The person she remembered most: Marwan Al-Shehhi, who was listed aboard United Airlines Flight 175.

She said the pudgy, bespectacled man asked her about good restaurants in the Delray Beach area.

“He looked me right in the eye and asked, and then everybody jumped in - all the people at the computers,” she told reporters.

“The place was bustling, and all these people started telling him about the restaurants in Delray. It makes me angry. It's so upsetting. They were here using our library as a vehicle for terrorism.” FBI agents have since carted away three of the computers.

Casey Brown, the former assistant Palm Beach County property appraiser, said he uses the computers there so often “I probably sat next to those guys and didn't even know it. Delray has people from every walk and color. They would not have turned any heads.”

But there were people who ran into the terrorists who said they acted strange and standoffish and didn't say a lot.

The wife of the flight instructor who allowed Atta and Al-Shehhi to stay in his home asked her husband to throw them out. They were rude, she said, and scared her.

The trainers at the World Gym in Boynton Beach said the terrorists did not appear to know how to use the equipment, and often huddled among themselves, talking in hushed tones.

The only brush with the law occurred in April, when Atta was issued a traffic ticket in the Fort Lauderdale area for driving without a license. He never appeared for his May 28 court date.

He and Al-Shehhi often went to a Denny's restaurant in Delray Beach, ordering black coffee and veggie cheese omelets, according to employees.

“They were regulars,” said waitress Donna Cooper.

Just days before the hijackings, two of the terrorists checked into the Panther Motel in Deerfield Beach, a small city about 18 miles north of Fort Lauderdale. Co-owner Richard Surma remembers them well.

“They paid me $500 in advance,” he said. His wife, Diane, said she gets chills when she recalls how Marwan Al-Shehhi stood so close to her. “He was right there talking to me in the laundry room.”

Before checking out the day before the attack, the terrorists left something behind in the Dumpster, said Mr. Surma: A flight tote bag stuffed with FAA flight maps, a protractor, martial arts books, an English-German dictionary, and a binder filled with scrawled notes.

Between Aug. 24 and 29, the terrorists sealed their fates: At least 14 of the 19 booked reservations for the death flights.

Three provided the same Delray Beach address. Six of them gave the same Broward County cell phone number. Some paid cash, and others used credit cards, logging onto the Internet to book their tickets.

They began to leave for Washington, Boston, and New York by late August and early September.

Some experts speculate that the remaining terrorists in South Florida began to show the strain of their upcoming mission on Sept. 7.

That's when Atta and Al-Shehhi ventured to Shuckums, a popular bar in Hollywood, an old coastal town south of Fort Lauderdale. There, the two appeared to be agitated as they downed several cocktails.

Night manager Tony Amos told reporters he asked the men if they could afford the $48 bar tab, and Atta became angry.

"He said, 'I'm a pilot from American Airlines, and I can afford to pay my bill,''' said bartender Patricia Edrissi. He paid the bill, leaving a $3 tip.

Some South Florida residents are coming to grips with the realization that they may have crossed paths with the terrorists during innocuous trips to the beach, grocery store, library, or even a restaurant.

"It's shocking beyond belief that these guys were here," says Dr. David Niven, a Delray Beach resident and professor at Florida Atlantic University. "While 8-year-old kids were doing their homework at the library, these guys were sitting next to them planning to blow up the World Trade Center."

While he and others are baffled the terrorists lived among them, Mr. Brown insists there was no way anyone could have known of the horrors they were about to carry out. Most of the immigrant groups that come to South Florida keep to themselves and speak a foreign language, he says.

""Every nationality in the world is within a five-mile radius of my house. And if they lived next door to me, I doubt if I could even pick them out of a police lineup."

The Blade's wire services contributed to this report.