London's Dirty-Bomb Plot

When British authorities broke up a cell of suspected Islamic terrorists in August, the arrests sent reverberations across the Atlantic. Among the evidence found with the suspects were reconnaissance reports on major U.S. financial sites—including the New York Stock Exchange and the World Bank in Washington.

But senior U.S. law-enforcement officials tell TIME they are continuing to follow the case closely and are learning even more disturbing details about what the group may have been plotting.

Reports on the British investigation, now circulating among U.S. law-enforcement agencies, assert that the group was trying to construct a crude radiological dirty bomb. The arrests (which followed a yearlong surveillance operation, code-named Operation Spangle) turned up a cache of household smoke detectors, which the British suspect the group wanted to cannibalize for their minute quantities of americium-241, a man-made radioactive chemical.

Officials tell TIME it's extremely unlikely that enough americium could be harvested from smoke detectors to create a device potent enough to inflict radiation sickness, let alone kill people. But others argue that spewing even a small amount of radioactive material into a crowded stadium or subway station could trigger sensitive radiation sensors, incite panic and cause long-lasting contamination.

Law-enforcement officials tell TIME that information from computer files seized with the group revealed plans for specific attacks in London, including "blowing up high-rise buildings housing multinational companies" by driving bomb-laden cars into underground garages. Other targets included the Heathrow Express, a rail line between the airport and London, and an unspecified synagogue. There were also plans for "hijacking a gasoline tanker and smashing it into a building." The British cell leader, Dhiren Barot—a.k.a. Issa al-Hindi—traveled to New York City in early 2001, according to The 9/11 Commission Report, "to case potential economic and 'Jewish' targets." U.S. officials hope to learn from the continuing investigation whether a sleeper cell remained in the U.S. to carry out these missions.