MINNEAPOLIS (WCCO) – Aurora, Newtown, Boston. All are sites of horrible mass killings. But only the Boston bombings have been labeled an act of terrorism.

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When is an act of violence a crime and when is it terrorism?

Eric Schwartz is dean of the University of Minnesota’s Humphrey institute, and a former assistant secretary of state and staffer at the National Security Council. He says the definition is not always clear.

“You will read that there are over a hundred definitions of terrorism”, Schwartz said. “What terrorism involves is a combination on the one hand of a violation of the law that’s generally connected to the effort to coerce or intimidate to achieve a political aim.”

Schwartz says government officials often “hotly debate” on whether to label a specific crime, like the Boston Marathon bombings, as an act of terrorism.

Because the motives in the Boston bombings are not clear, the U.S. made the call to label this a terrorist case on the facts so far.

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“It’s a presumption based on the fact that it’s kind of hard to conceive of what else it might be,” he said.

The terror label allows the government to use investigative techniques and evidence gathering that it can’t use in criminal acts.

“The government is given under the Patriot Act additional tools with respect to wiretapping,” he said.

And the “terror” label brings with it additional and often greater punishments.

“For a terrorism-related activity, there are very significant civil and criminal penalties under the Patriot Act,” he said.

Schwartz says the terrorism label also allows the government even greater powers when a suspect is not an American.

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If Dzhokhar Tsarnaev wasn’t an American citizen, he could have been tried in a military court as an enemy combatant. Instead, he’ll be prosecuted in the federal court system.

Esme Murphy