The trail of the Tsarnaevs seems, for the moment, to remain one of lone wolves. But counterterror operatives see details that suggest a wider organization may yet be discovered. Most telling: the sheer firepower the Tsarnaevs were able to bring to bear in their shootout with police. They appeared to have several unused bombs. And because terrorists learn from each other’s actions, some counterterror analysts are speculating that they may have planned a bigger operation at the marathon, or perhaps to come. One possible example is the bloody Mumbai attack in 2008, carried out by a handful of men, which killed 164 people. “These are ‘wise guys,’” said one veteran counterterror official. “These are intelligent individuals who thought they could outsmart everybody and get away with it. They didn’t want to die. But they prepared a lot of stuff.”
This doesn’t mean al Qaeda played no role: on the question of whether the lone wolves had domestic or international grievances, officials thought it likely that they were “inspired” by al Qaeda’s ferociously anti-American ideology, which paints the United States, essentially, as the root of all evil. . . .
The bombs used in Boston were improvised explosive devices, IEDs, made from everyday pressure cookers filled with easily fabricated explosives as well as nails and ball bearings to act as shrapnel. Investigators believed that could point to al Qaeda-inspired individuals. Jihadist guerrillas in Afghanistan, Pakistan, Iraq, and India commonly use such IEDs. But the bombs could also have been related to domestic terror. After all, the last man to attack strangers with an IED in the United States was Eric Rudolph, who planted a bomb at the 1996 Olympics in Atlanta.