U.S. Responded to Plot with Speed, Secrecy

Until the last hours, details of the British probe were confined to a limited coterie of U.S. Cabinet members and senior officials.

In late July, the British became "exceptionally concerned about where the specifics of the investigation were leading them -- it was getting more from conception to completion," one official said. Chertoff publicly described this as the moment "that the investigation revealed that this planning was taking the direction of targeting the United States."

Within days, the FBI was hunting down names provided by British intelligence and police, seeking to identify any domestic tentacles of the suspected plot. FBI Director Robert S. Mueller III, who took over the bureau just days before the Sept. 11, 2001, attacks, cleared most of his schedule to concentrate on the probe around this time, aides said.

More than 200 FBI agents and scores of analysts and other personnel would be assigned to the operation in late July and early August, mounting dozens of clandestine surveillance and search operations on individuals with possible links to the London plotters, officials said. Among the individuals were people who had been called or e-mailed by suspects or their relatives and acquaintances, as the FBI combed through layers of the group's "social network" inside the United States.

The case included labor-intensive 24-hour surveillance, which can require several dozen people to watch a single target, one official said. Those conducting the surveillance generally had no idea why the subject was being watched, the official said.

The volume of surveillance was such that it produced a noticeable surge in applications for clandestine warrants from the Foreign Intelligence Surveillance Court, which oversees most intelligence surveillance inside the country, according to law enforcement officials.

By Friday, Aug. 4, "the real countdown started," one U.S. counterterrorism official said, as British authorities finalized plans to proceed with arrests. U.S. officials were given a rough schedule that broke down the planned "timing and the conduct of the takedown," Jackson said.

Senior government intelligence officials, along with leaders of the Defense, Homeland Security and Justice departments, began preparing for the possibility of attacks on jetliners over the Atlantic, with options including destruction of one or more aircraft, a disrupted attack, and the capture of all suspects.

On Aug. 5, President Bush was given briefings at his Crawford, Tex., ranch about the government response in case an attack materialized, officials said. Hawley, the TSA chief, was called back from a trip to participate. Information was limited to "a small handful of individuals," Jackson said.

One U.S. official said the circle initially excluded staff aides at the National Security Council, the Homeland Security Council and the Counterterrorism Security Group, all of which are usually deeply involved in sensitive terrorism cases.

The arrests on Thursday occurred at least two days earlier than planned, according to several U.S. officials. Among other things, sources have said, the suspects stepped up their Internet searches for possible U.S.-bound flights, made plans for an imminent "dry run" to test security, and moved to purchase global-positioning satellite devices and other materials. British authorities were also concerned because they had lost contact with one or two of the suspects who had traveled to Pakistan, some officials said.

Given a schedule from London, senior U.S. and British government officials consulted Wednesday between 6 p.m. and midnight Washington time. It soon became clear that all the suspects could not be located immediately, raising concerns about a potential attack.

"As things headed south," one official said, Chertoff "flipped the switch" to gain approval for raising the threat level. Late Wednesday and into Thursday, DHS leaders held a series of conference calls with governors' offices, airlines, airline security specialists, labor unions, and airport security directors across the country to share information and plans.

Chertoff joined the 8 p.m. call with the security directors, saying this moment was the reason they did their jobs. Shortly afterward, TSA issued its official "security directive" banning all liquids and gels from carry-on luggage, giving airports and airlines about four hours on the East Coast to prepare more trash bins, print fliers and call in reinforcements.

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