A plan to crash a plane into CIA headquarters was exposed after an arrest in the Philippines. A meeting of future Sept. 11 hijackers aroused suspicion in Malaysia. Information that al-Qaida was seeking to assassinate President Bush at a summit in Europe led to heightened security.
Clues filtering in from overseas since at least 1994 foreshadowed Osama bin Laden's plans to attack America, and intelligence information from Italy, Israel and elsewhere in the months before Sept. 11 warned that a terrorist strike might be imminent.
The White House acknowledged Thursday that President Bush was briefed by the CIA on Aug. 6 about an al-Qaida hijacking threat. An earlier report by the Phoenix field office of the FBI that may never have reached the president's desk warned that many Middle Eastern men were training at least one U.S. flight school.
The Bush administration said the information was not specific and there was no intelligence before Sept. 11 that al-Qaida planned to use commercial planes as vessels of destruction.
But warning signs that something like Sept. 11 might be contemplated weren't all recent and they came from different sources around the world.
Warnings from abroad
In 1994, Algerian militants hijacked an Air France jetliner and killed three passengers before being captured during a stop in Marseilles. It came out that they had hoped to blow up the jet over the Eiffel Tower, debunking the notion that a suicidal airline attack on a prominent target was unthinkable before Sept. 11.
Perhaps the first clue of a similar plot against the United States emerged during the Clinton administration in 1995, when Philippine authorities arrested Ramzi Yousef and Abdul Hakim Murad after a chemical fire at their Manila apartment.
Under questioning, Murad admitted connections to bin Laden and spoke of a plot to dive-bomb a jetliner into the CIA headquarters in Langley, Va. He also said Middle Eastern pilots were training at U.S. flight schools in preparation for a plot to blow up 12 passenger jets over the Pacific Ocean.
The FBI was alerted at the time and interviewed flight school attendees, but it did not develop evidence that any of the Middle Easterners were plotting terrorism.
FBI and other law enforcement officials involved in the Murad investigation, who spoke earlier this year on condition of anonymity, said American authorities were focused mostly on the plot to blow up the airplanes because it was developed and imminent when Murad and Yousef were arrested. The plan to use a plane as a weapon was largely discounted.
Yousef, considered the mastermind of the 1993 World Trade Center bombing, and Murad were eventually convicted in the United States and sentenced to life in prison.
Administration under fire
Larry Johnson, deputy director of the State Department's office of counterterrorism in 1989-93, criticized Rice for discounting the possibility that a Sept. 11-type attack could have been foreseen.
"She's foolish in saying that. Intelligence analysts are paid to imagine the unimaginable. That information was in their files, and if they weren't imagining it, that is a failure of intelligence and a failure of imagination," he said.
Other clues, connections
Another clue to Sept. 11 came in 2000, and it was partially a result of the 1995 Philippine investigation.
The investigation of Murad and Yousef led authorities to a radical Indonesian cleric, Riduan Isamuddin, who was living in Malaysia and was suspected of deep ties to al-Qaida and other terrorist organizations.
The cleric, who goes by the name Hambali, was under surveillance in January 2000 when he met with two future Sept. 11 hijackers Saudi nationals Khalid Almihdhar and Nawaf Alhazmi in Kuala Lumpur, Malaysian authorities have said.
Information from the surveillance was shared with U.S. authorities, and the meeting took on new significance when another of the participants, an unidentified al-Qaida operative from the Middle East, became wanted in connection with the October 2000 attack on the USS Cole.
The two Saudis were not on the intelligence community's radar screens at the time, but their connections to Hambali and the al-Qaida operative wanted in the Cole investigation got them placed on a CIA terrorist watch list in August 2001 one month before they helped commandeer the American Airlines jetliner that crashed into the Pentagon on Sept. 11.
The investigation into Hambali has also linked the cleric to another alleged Sept. 11 player, Zacarias Moussaoui, who is on trial in U.S. District Court in Virginia and faces the death penalty if convicted of conspiracy in the attacks.
Two of Hambali's followers, Yazid Sufaat and his wife, Sejahratul Dursina, are under arrest in Malaysia Sufaat in connection with a plot to blow up the U.S. Embassy in neighboring Singapore and Dursina for allegedly providing Moussaoui with an employment letter that helped him get the U.S. visa.
Moussaoui was arrested on a visa violation in August after raising suspicions during flight training in Minnesota.
French intelligence was aware of Moussaoui as early as 1999, when he was placed on a watch-list for alleged links to the Armed Islamic Group, which claimed responsibility for 1995 bombings in the Paris subway.
Whether that information was shared with U.S. officials is not clear, and Moussaoui was granted a U.S. visa to train as a pilot in the United States.
Threat to president, others
In addition to intelligence about specific Sept. 11 participants, there were signs last summer that al-Qaida was planning a major strike.
Egyptian President Hosni Mubarak said his country passed along information to Washington about a possible threat on President Bush's life at the Group of 8 summit in Genoa, Italy, following a June 13 video made by bin Laden.
Italy closed Genoa's airspace and mounted a short-range, anti-aircraft battery at the airport during the July 20-22 summit, Deputy Premier Gianfranco Fini said.
"Islamic extremists were said to be trying to hit Bush in the air," Fini said.
Another clue of terrorist rumblings came from Djamel Beghal, a 35-year-old French-Algerian arrested in Dubai last July with a false passport. Under questioning, Beghal detailed an al-Qaida plot to blow up U.S. interests in Europe, including the American Embassy in Paris.
Beghal said he met bin Laden operatives at mosques in Britain, traveled to Afghanistan for weapons training at an al-Qaida camp, and met at bin Laden's home with his top aide, Abu Zubaydah.
European authorities began looking into the plot on Sept. 10.
Israeli intelligence services were aware several months before Sept. 11 that bin Laden was planning a large-scale terror attack, but did not know what his targets would be, Israeli officials have said.
An Israeli official, speaking on condition of anonymity, told The Associated Press shortly after the attacks that "everybody knew about a heightened alert, and knew that bin Laden was preparing a big attack."
He said information was passed on to Washington, but denied Israel had any concrete intelligence that could have been used to prevent the Sept. 11 attacks.
Boaz Ganor, head of the International Policy Institute for Counter-Terrorism in Israel, said the type of warning described by the Israeli official would have been too abstract for U.S. officials to act on.
"I don't think it would have helped American intelligence," Ganor said. "That's not enough information to make a difference. The number of warnings that Western security services get in a day are in the hundreds and at the end of the day most do not pan out. Intelligence services need concrete warnings such as a date, the names of the perpetrators or their methods."
The final sign that something was afoot may have come Sept. 9, when suspected bin Laden operatives posing as journalists assassinated Gen. Ahmed Shah Massood, leader of Afghanistan's anti-Taliban northern alliance, in a suicide attack at his headquarters.
U.S. officials have speculated the killing was designed to deprive the northern alliance of its boldest and most experienced leader just days before attacks on New York and Washington that bin Laden must have known would prompt a U.S. response against his Taliban hosts.