The full biographies of the brothers who carried out the Boston Marathon bombing are still coming into focus. What we do know is that the Tsarnaevs are Muslims; that they've lived in the U.S. for more than 10 years; and that the younger brother, Dzhokhar, became a U.S. citizen last year. By most accounts the men seem to have had no prior history of violence and embarked on a path of radicalization relatively recently. The investigation will continue, but for the moment the brothers more closely fit the description of "homegrown" militants than that of international terrorists.
This is largely what counterterrorism experts expected. As I wrote in this week's print edition of Bloomberg Businessweek, because the U.S.'s campaign against al-Qaeda has been so effective in dismantling the organization's capabilities:
"Acts of terrorism against the U.S. are less likely to be committed by a global enterprise like al-Qaeda than by small numbers of 'self-radicalized' domestic jihadists, far-right hate groups, anarchists, and radical environmentalists. Because they're more diffuse, these potential perpetrators are also harder to identify and stop."