New York After the 1993 attack on the World Trade Center, investigators discovered that conspirator Nidal Ayyad had left behind a chilling computer message: "Next time, it will be very precise."
The note along with evidence from past cases of terrorism gives insight into a more than decade-long learning curve that culminated in the devastating Sept. 11 attack.
At the outset, poorly funded and mistake-prone terrorists labored to develop technical expertise to kill large numbers of people with bombs. But a review of New York terrorism cases shows a pattern of growing sophistication, far better financing and more elaborate planning.
Conspirators moved away from the use of explosives; began employing suicide missions as a primary tactic; plotted simultaneous strikes at multiple targets rather than single locations; and halted public activities that could connect them with religious or political zealots.
"Terrorists have not only long memories, they have infinite patience," said Edith E. Flynn, professor of criminal justice at Northeastern University. "They certainly learn from their mistakes. "
Robert Blitzer, former chief of domestic counter-terrorism for the FBI, said the use of would-be martyrs has given terrorists a wicked weapon. "They have moved forward by enlisting more people willing to give up their lives for their idea of their religion," Blitzer said.
"They've constantly looked for bigger and better ways," he said. "This has been a logical progression."
The financial picture for terrorists has improved considerably, too. The mastermind of the 1993 World Trade Center attack when a bomb planted in a van in an underground garage exploded, killing six people said the strike occurred at the end of the month because the perpetrators had run out of rent money.
Court testimony shows the 1993 trade center conspirators spent only about four months plotting the attack, and drew on a bank account of less than $10,000. The Sept. 11 attack was planned over several years and bankrolled with $500,000, according to a law enforcement official who spoke only on condition of anonymity.
The 1993 trade center conspirators were known to have attended lectures led by militant Sheik Omar Abdel-Rahman. The Sept. 11 conspirators took great pains to blend seamlessly into their communities.
Flynn said terrorists learn from court trials such as the one this summer in which four of Osama bin Laden's followers were convicted in the Aug. 7, 1998, bombings of two U.S. embassies in Africa. The trial revealed that the terrorists had become suspicious of potential informants in their midst.
"They are following those trials and they're looking at the evidence," Flynn said. For instance, she said, the use of government wiretaps in a series of cases over the past decade appears to have made terrorists less reliant on telephones.
In New York, court testimony shows, the FBI's early encounters with Middle East terrorists came in 1989, when agents trailed visitors to a Brooklyn office that recruited Muslims to fight in Afghanistan.
An FBI agent observed two of them training with guns on Long Island. With them was El Sayyid Nosair, who in 1990 assassinated militant rabbi Meir Kahane in Manhattan.
At the time, Nosair was considered a crazed, isolated gunman. It wasn't until after the 1993 trade center bombing, which resulted in the convictions of his two Long Island companions, that the FBI realized he was part of a terrorism network.
Know your enemy
Soon, the FBI was treating terrorists like organized crime, relying heavily on wiretaps, surveillance and turncoat defendants to learn about its adversary.
Using a $1 million informant and wiretaps, the FBI unearthed a plot in mid-1993 to blow up the United Nations, FBI headquarters, two tunnels and a bridge.
The wiretaps caught the architect of that failed mission mocking the 1993 trade center bombers especially one who rented a van in his own name and then returned after the attack to collect a $400 deposit. The FBI was waiting for him.
"They're all stupid of course, but he's the stupidest one of them all because he is the one who screwed up the whole thing," Siddig Ibrahim Siddig Ali said. But Siddig Ali was caught, too, and pleaded guilty in the landmark plots. He cooperated with prosecutors, earning an 11-year prison sentence.
Trade center bombing mastermind Ramzi Yousef was disappointed that he had not toppled the twin towers in 1993, but he was undeterred. He fled the country the night of the attack to plot more terrorism.
After explosives caused a fire at his apartment in the Philippines in early 1995, investigators learned he was plotting to blow up 12 U.S. airliners over Asia in a spectacular attack meant to kill 4,000 people.
Investigators tracked him down before he could carry out his plan. But the airline and landmark plots show that, by then, the lesson of targeting multiple sites had become part of the terrorist textbook.