"That's definitely him. I'm really scared now," Ana Christina Fernandes told a British policeman Thursday as he showed her a picture. A grainy CCTV (closed circuit television) photo showed a young man in tracksuit pants and a white tank top boarding the No. 220 bus. She identified Osman Hussain as her London neighbor.
A day later, the same man, who police say tried to set off one of four bombs on July 21, was captured by Italian police in Rome. He was betrayed by his mobile phone. Mr. Hussain was using a relative's cellphone as he traveled from Britain to France and Italy. By tracing the phone, Italian police pinpointed Hussain's location. This weekend, police say, they captured all four of the 7/21 London attackers, and technology proved a crucial tool in cracking the cases.
"There are a lot of lessons for other European capitals about using CCTV for both prevention and tracking of terrorism," says Magnus Ranstorp, a terrorism expert at St. Andrews University in Scotland. "I doubt very much that the 7/21 bombers would have been caught so quickly had there not been CCTV cameras that allowed police to work with the public."
Britain's investigation into the bombings which have twice struck London in three weeks has been sped along by the use of new and evolving technologies like CCTV and mobile phones, which have allowed police to identify suspects quickly and trace their movements around the world.
The string of contacts - and arrests - continued over the weekend. Police arrested six people Sunday they say were involved in the failed July 21 London transit bombings and were reportedly investigating the attackers' ties to Saudi Arabia and Italy, hurrying to track down any accomplices to prevent more attacks.
Police sources told the Sunday Telegraph that Mr. Hussain, an Ethiopian-born British citizen, called Saudi Arabia hours before his arrest. A legal expert familiar with the investigation told the Associated Press in Rome that Hussain admitted to a role in the attacks but said it was only intended to be an attention-grabbing strike.
Hussain told Italian police that the bombers had been led by a man called "Muktar," the Rome daily La Repubblica reported.
Suspect Muktar Said Ibrahim was arrested Friday in London. The Sunday Times said the Ethiopian-born Briton went to Saudi Arabia in 2003 on a month-long visit, telling friends he went for training.
In Pakistan, police are painstakingly analyzing the mobile phone records of the two 7/7 suspects who visited the country. While officials stress that it is a tedious process, it has already yielded the name of at least one significant suspect: Masoud Azhar, leader of the Jaish-e-Mohammed (Army of Mohammed).
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.