It's an almost impossible task for investigators, and if weren't for the fact that human lives are at stake, it would be the height of absurdity. Ever since the July 7 terrorist attacks in London, German police have been looking for men whose most-unique trait is the fact that they don't stand out at all. Investigators are now looking for young Muslims, between about 18 and 30 years of age, who have grown up in middle-class families and lived relatively sheltered lives. It's a profile that already began taking shape after the 2004 Madrid train bombings.

"We have to stop focusing exclusively on attackers or sleeper cells who come here from abroad," says Jörg Schönbohm, the Christian Democratic interior minister of the German state of Brandenburg, summing up the shift in attitude.

German investigators have stepped up their efforts to search for Muslims who grew up in Germany and may have become radicalized, albeit under the radar. The first thing the authorities have done is to monitor the activities of those on the German Federal Office of Criminal Investigation's list of leading potential terrorists. Three-quarters of the 105 Islamists in this category have been located, but about 30 couldn't be tracked down immediately. Investigators have also begun wire-tapping every telephone conversation in the radical Muslim scene, and undercover agents are infiltrating some of the more suspect mosques to gauge the mood.

A special team of officials at Germany's joint federal and state counterterrorism center set up to investigate what it calls "Islamist/terrorist manpower potential" began combing through the center's files last week. They're looking for answers to questions like: Who could have drifted unnoticed into the militant milieu? Where are there connections between radicals and unknowns?

Germany's Federal Office for the Protection of the Constitution maintains a list of about 300 Islamists seen as the hard core of the radicalized scene. Although about twice as many are considered part of their extended sphere of influence, the lesson from Leeds is that suicide bombers don't necessarily have to be part of either of these groups. One German official puts it bluntly when he says that the London terrorist attacks have confirmed "our fears." Meanwhile, Uwe Schünemann (CDU), interior minister of the state of Lower Saxony, warns that Germany must also "prepare for such attacks."

Germany has been lucky so far. Many young radical Muslims, like Tarkan K. from Munich, have already left the country to fight elsewhere. The 31-year-old, whose life story is eerily similar to that of the man British tabloid The Sun dubbed the "Boy Bomber" from Leeds, grew up in the staunchly middle-class suburb Neuhausen. For most of his life, he was considered an affable fellow. But then, at 22, he suddenly donned the long robes of the conservative Muslim and disappeared in the direction of Pakistan. Like two of the London terrorists, Tarkan K. was put in touch with radical groups there by traveling imams associated with Tablighi Jamaat, a religious organization active in Europe and now suspected of radicalizing British Muslims.

Fellow travelers later reported that Tarkan K. learned how to build bombs in the Hindukush region. He's now in prison in Turkey, after Turkish authorities tied him to terrorists who set off an explosive device in front of the British general consulate in Istanbul in 2003.

While politicians squabbled last week over counterterrorism computer files and increased video surveillance, those involved in the more practical aspects of fighting terror were uncharacteristically unanimous about one thing: Solving the problem will take more than just suppression -- prevention and integration are just as important in the long run.