High-tech tracked London suspects

But the clever use of technology is not the exclusive domain of law enforcement. It is equally a tool of terrorists. "The instruments of globalization have afforded [terrorists] a great degree of anonymity and mobility," notes Mr. Ranstorp, citing terrorist organizations' fondness for pre-paid phone cards, one-time use satellite phones, and coded e-mails as means of coordinating their activities.

Terrorist organizations have also made use of technology to distribute both their ideology and training. Islamist websites show slickly produced instructional videos on such things as building bombs and pulling off a successful kidnapping. And in the event the hostage is executed, the videos can be shown online to a world audience to simultaneously recruit new terrorists and sow fear.

When the police make swift progress, Ranstorp says, it's often because the terrorists may have made mistakes in their use of communication technology. "It's a double-edged sword," he says. "It depends on how well-versed [terrorists] are at covering their tracks. If they are careless, all the police need is one break."

Suicide bombers in particular, he says, are less likely to care about concealing their support network so long as they are able to carry out their attack. "In Madrid, there were a lot of people on the periphery of the [May 2004] bombings who were expendable," says Ranstorp.

In Britain, as CCTV cameras have sprouted across the land during the last decade, more Britons have joked - and civil libertarians have complained - that they have become the most watched people on earth. It's estimated that there is one camera for every 14 people here; in big cities like London, it can mean that nearly all a person's movements from the moment he or she leaves the house are caught on tape.

But it is a boon to police investigators working frantically to avert expected further attacks. In the course of the London bombings' investigation, they have scrutinized some 15,000 CCTV tapes. After the 7/7 bombings, the release of images of the four suspects triggered hundreds of calls and e-mails; a subsequent series of raids netted an abandoned car, with leftover explosives, which helped police identify the bombers.

Last Thursday, 6,000 police fanned across London in the largest security exercise since World War II. The blunt, boots-on-the-ground show of force had been prompted, police officials announced Sunday, by intelligence suggesting that a third Islamist terror cell is planning a wave of suicide attacks on "soft targets" in central London such as the Tube.

Science and technology are critical tools. But Metropolitan Police Commissioner Sir Ian Blair stressed to the BBC this weekend the importance of tried-and-true police assets: firepower, forensic experts to analyze bombs and bomb traces, and "good old-fashioned detective legwork."

• Wire services were used in this report.

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