Put aside, for a moment, whatever you might suspect about anyone’s motives for bombing the Boston Marathon, since no one actually knows yet. One prominent expert on extremism and radicalization thinks the crucial step for detecting and stopping the next would-be bomber is to bone up on psychology.

Not even the FBI ultimately suspected accused bombers Tamerlan and Dzhokhar Tsarnaev were about to plant deadly bombs that killed three and wounded about 180 last week. Extremist violence can be like that. “Because their outward behavior was so normal,” Roger Griffin, a professor of political science at Oxford-Brookes University tells Danger Room, “they weren’t picked up as a threat.”

Griffin would know. Having built a career studying far-right extremism, Griffin shifted to studying domestic radicalization — including advising the British Home Office — after the “7/7″ bombings in London by a group of domestic terrorists in July 2005. He believes violent extremism of any variety should be understood less as a political phenomenon than as a psychological state — particularly, as a form of destructive and self-destructive behavior that’s rooted in feeling disconnected from the modern world.

When looking at the Boston bombings, Griffin can’t help but see parallels to the 7/7 attacks. In both cases, the suspects were either born or spent years living in the U.S. and Britain: the Tsarnaev brothers lived in the U.S. for nearly a decade. One member of each group was once investigated by the authorities, but to no effect. There are also some differences: The London bombers left a videotaped manifesto declaring their motivations, whereas the Tsarnaev brothers’ motivations are unknown as yet. The London bombers’ attacks were also suicidal.

But in both cases, no one noticed before it was too late.