MINNEAPOLIS (WCCO) — Home video shows the attack on the Charlie Hebdo headquarters in Paris Wednesday that left at least 12 dead, including four of the magazine’s founding cartoonists and the editor in chief.

As the gunmen got away, they killed a responding police officer who they had first shot on their way in the building.

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In Washington, President Obama expressed his sympathy and his support.

“We will stand with the people of France through this very, very difficult time,” President Obama said.

The attackers told witnesses to tell the media Al-Qaeda in Yemen were responsible.

Charlie Hebdo magazine enraged Muslims in the past for publishing cartoons depicting the Prophet Muhammad.

Jane Kirtley is the Silha Professor of Media Ethics and Law at the University of Minnesota’s School of Journalism and Mass Communication. She says journalists may be more at risk today because of technology.

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“Their editor said he would rather die standing than on his knees and he was not prepared to cut back on what he thought he needed to be doing, which was holding these kinds of people into account,” Kirtley said.

She also says the ability for publications to reach a larger audience online is another risk factor.

“I think the instantaneous nature of communication has changed the nature of the reactions.”

While police work to figure out how the attack happened, thousands have gathered in Paris to show their support for the victims — and free speech — while chanting, “Je Suis Charlie,” or “I Am Charlie.”

“Freedom of the press, like any other freedom, is not free,” Kirtley said. “Sometimes people have to pay the ultimate price to defend it.”

Eleven others were injured in the attack, four of whom are in critical condition.

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French authorities have identified three suspects. Two of them are French-born brothers in their early 30s. The third is 18, but his nationality is unknown as of Wednesday evening.

Kate Raddatz