By Audrina Bigos

(CBS) — A former ATF special agent talked to CBS 2 why the mass shooting in San Bernardino which has left 14 people dead is so different from those we’ve seen this year.

Cynthia Beebe just retired after 27 years as an ATF special agent. She now trains law enforcement on how to respond to mass shootings and how to engage shooters faster.

“Three heavily armed, trained shooters attacking an apparently non-descript building,” Beebe said.

She says that’s what makes this shooting so unusual for officers responding, the possibility of not one, but as many as three suspects.

“The more uncertainty in any situation, the more difficult it is,” she said. “Every room has to be approached as if there’s an active shooter potentially in that room.”

A woman in one of the rooms called her sister.

“The police, and they came in and they told everybody that they needed to hurry up and get out,” said Stephanie Baldwin.

That not long after, “The shooters came in and they just started unloading rounds.

An apparent explosive device left at the scene she says also added an element of difficulty.

“What’s of crucial importance is how big of an explosive is it?” Beebe said.

While apparent victims walk out one by one with their hands up.

“It would be almost impossible for that shooter to reach down and draw a weapon and fire before he is shot,” Beebe said.

She says this appears to be a well-planned, well-organized attack — hence, these suspects are able to flee.

Beebe says, from her experience and what she knows so far about this shooting, this does not appear to be an act of terrorism.

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