Chelsea bombing: Why isn’t the mayor calling it terrorism?

NEW YORK -- When New York's mayor steered clear of calling a bombing in his city a terror attack, it wasn't long before critics slammed him with a common refrain.
"It's clearly terrorism -- why doesn't he just come out and say it?"

But there's a good reason to be cautious about labeling violence as terrorism, says CNN national security analyst Juliette Kayyem.

"When investigators and politicians are unwilling to say it's terrorism, it's not because they're 'PC' or anything like that, it's just that the investigation has to unfold naturally," she says.

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There's a specific definition of terrorism that investigators and officials use, Kayyem says.

The definition: The purposeful attack on a civilian population for political or ideological means.

The New York attack meets two of those; the bombing was intentional and it injured civilians.

But there's a key element we don't know yet: The bomber's motive.

"That we don't know yet," Kayyem says, "mostly because we don't know who the culprit is." Investigators say they want to question a 28-year-old New Jersey man in connection with the bombing, but they haven't called him a suspect.

Calling something terrorism too soon, Kayyem says, can point investigators in the wrong direction as they search for suspects.