In Boston, authorities are investigating whether a Lebanese man who claims to have attended an Al Qaeda training camp is part of a larger sleeper cell in the region. Other probes focus on cities in Texas, Florida, Michigan and the Carolinas, authorities say.
And in California, authorities are pursuing leads that Al Qaeda is operating on both sides of the Mexican border, and that the group continues to be interested in launching attacks against high-profile targets in Los Angeles and San Francisco.
In some cases, authorities are closely monitoring suspects, often using secret wiretaps and search warrants obtained through the Foreign Intelligence Surveillance Act to determine whether they are raising money, recruiting operatives or providing logistical aid to terrorist groups, or even playing operational roles in plots against U.S. targets.
Authorities are also investigating several dozen other individuals and groups that have no visible connections to known terrorists, including two young men of Pakistani descent who were arrested last week on suspicion of plotting a "holy war" rampage in New York City. Authorities said those plans included blowing up subway stations, police precincts and bridges.
Babar's case appeared to be unique, authorities said, in that he had admitted having personal contact with several high-ranking Al Qaeda members and playing a role in a plot by the group to blow up pubs, restaurants and train stations in London. Babar has admitted providing the London group ammonium nitrate and other materials to make bombs.
British authorities thwarted that alleged effort in March, arresting eight suspects. Authorities also seized 1,000 pounds of ammonium nitrate, a key ingredient in the 1995 bombing of the Alfred P. Murrah Federal Building in Oklahoma City and the bombing of two Bali discos two years ago.
Soon after the arrests, British authorities told their U.S. counterparts that Babar appeared to be a co-conspirator. He had already been placed on an FBI terrorism watch list, after a Canadian television program broadcast footage of him from Pakistan making inflammatory remarks.
Babar said he was a Muslim first, an American second, and that he wanted to fight with the Taliban against U.S. forces in Afghanistan and Pakistan.
"I'm willing to kill Americans," he told the reporter on the program, even as he asserted that his mother had worked in one of the World Trade Center towers and barely escaped with her life on Sept. 11. He also said he would never return to New York.
