Evidence seems to indicate that an organized group planned the attacks, using "sleeper cells" (terrorists who lived and worked in London and were called into action). If that's the case, Americans may face a similar problem.
To talk about that possibility, Jessica Stern, author of "Terror in the Name of God," visited The Early Show Monday for an interview with co-anchor Rene Syler.
The timing of these bombings seems to indicate a level of sophistication. Authorities say they were made of highly explosive material and that they were set off with timers. What does all this tell Stern?
"It doesn't actually tell us all that much," says Stern. "But there are other clues that suggest that it's very likely that whoever this group was, they did get assistance from local, whether sleepers or people who self-radicalized as supporters of the al Qaeda movement, most likely."
Investigators say they're not sure if they were people who were brought in to actually carry out these attacks. But is it possible that these were sleepers, that they actually lived in the area and worked with the people against whom they were plotting?
"It's definitely possible," Stern asserts. "Britain has long been a center for infamous ferment. There are people who have been ready to carry out terrorist crimes there for quite a while. We know that some of them even have gone to Iraq, and some even are coming back to Europe after going to Iraq.
Is it possible that sleeper cells are poised to strike in the U.S.?
"Yes, unfortunately that definitely cannot be ruled out," says Stern. "We know that there are some supporters of al Qaeda that have already been identified. For example,with a hare-brained plot. But this is something that we just have to live with, I'm afraid."
So how does one fight a movement like the one fostered by al Quaeda, a movement that is, says Stern, being facilitated by the Internet, "which allows young people to just read about the ideology and form their own cells or take action on their own."
She continues, "The advantage to knocking out the headquarters of al Qaeda is that we probably won't see another Sept. 11 in the immediate term. The disadvantage is that it's much harder to track these cells that are forming on their own."
What should the U.S. be doing that is not being done now?
"One thing, I think, is very important is that we start paying more attention to psychological clues," Stern recommends. "I can tell you that Massachusetts state police is training to look not just for, say, guns or plastic explosives but for people who look afraid. And I think that that is a very important and going to be a very useful development for reducing the threat of terrorism. Not just on planes but everywhere."