After receiving criticism for declining to use the word "terrorism" in his first response to the Boston marathon bombing, President Barack Obama invoked the term today, saying "any time bombs are used to target innocent civilians it is an act of terror."

Actually, that's not right. The U.S. federal code and the Federal Bureau of Investigation both include in their definitions of terrorism an element of political motivation.

Having spent nearly a decade based in Israel, I understand the common impulse to fit any grave disturbance into an obvious narrative. While politicians, commentators and bystanders can afford such assumptions, the responsible authorities cannot. I remember a particular car bombing in Israel, which the media, as a matter of course, treated as a terrorist act. Evidence later emerged proving the bombing was an internal mob hit.

The U.S. has mobsters too, and something else: mass killers who murder out of pure perversity. In other words, people who commit violence for its own sake and not to "intimidate or coerce a government, the civilian population, or any segment thereof, in furtherance of political or social objectives,” which is the FBI's terrorism definition. We don't consider the Aurora or Newtown killers terrorists. What if, in the case of Boston, someone like them used crude bombs instead of guns?

From the beginning, the most likely explanation of yesterday's bombings has been terrorism. Similarly, the most likely suspect in a murder case is often the boyfriend, but the cops don't start off their investigation by telling the press he did it.

We ought to be careful with the term "terrorism" not just for semantic reasons. Labeling an act as terrorism provides no answer for how to respond to it. Terrorism is just a means of fighting, and you can't wage war against a technique. You have to find the culprit.

(Lisa Beyer is a member of the Bloomberg View editorial board.)