An official who spoke on condition of anonymity because they weren't authorized to publicly discuss the investigation told The Associated Press that the men were linked to a Yemeni terrorist network. Cherif Kouachi was convicted in 2008 of terrorism charges for helping funnel fighters to Iraq's insurgency and sentenced to 18 months in prison.
Twelve people were killed in the attack by gunmen, armed with AK-47s, who attacked the offices of Charlie Hebdo, a publication that has enraged Muslims for publishing cartoons depicting the Prophet Muhammad.
A source familiar with the investigation told NBC News on Wednesday night that two officers who had been assigned to protect editor and cartoonist Stephane Charbonnier for the past several years came down from an upper floor and intercepted the gunmen. Both officers were shot, however, and one died at the scene. The other was wounded and is expected to survive.
The men targeted those magazine employees who had created or published cartoons showing Muhammad — asking for their victims by name, the source said. They executed Charbonnier, popularly known as Charb; Bernard Maris, a Bank of France economist who was a columnist for the magazine; and three cartoonists.
Outside the building, as the gunmen tried to flee in their Citroën van, three officers in a police patrol car intercepted them. Two suspects got out of the van, and one fired repeatedly into the windshield of the patrol car.
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The source said the patrol car driver slammed the car into reverse, while another officer in the car returned fire at the shooter. The patrol car driver then hit the brakes, allowing an officer in the back seat to jump out and run toward the suspects. But the officer was shot and wounded by the suspects. He was executed with a shot to the head as he lay on the sidewalk.
After killing the officer, the gunmen returned to their car, shouting, "We avenged the Prophet Muhammad," the source said.
Eleven other people were injured, four of them critically, officials said.
Because the masked, black-clad gunmen attacked with militaristic precision and left the scene with shouts of "Allahu Akbar," the killers were suspected to be well-trained Islamic extremists. In September 2013, Inspire Magazine, put out by al Qaeda in the Arabian Peninsula, published a "wanted" poster naming nine people whom Muslims should kill given the chance; Charbonnier was among the nine.
Little information was immediately available about Mourad and Said Kouachi, but Cherif Kouachi has been suspected of involvement in terrorist groups for at least a decade. In January 2005, he and another French national were arrested in Paris as they were planning to fly to Iraq via Syria. Kouachi was described at the time as one of two deputies to the leader of an operation to send young volunteers to Iraq to fight U.S.-led forces.
Authorities linked the 2005 operation to the 19th Arrondissement Network, named for the Paris district where it was based, which is home to many Muslim families with roots in France's former North African colonies.Kouachi was convicted in 2008 and sentenced to three years in prison, 18 months of which were suspended.
The Associated Press quoted Cherif Kouachi in 2008 as saying he'd been motivated by outrage at images of torture of Iraqi inmates at the U.S. prison at Abu Ghraib. "I really believed in the idea," it quoted him as saying.
While authorities hunted the suspects Wednesday, shock and mourning spread across Paris and the rest of France, a country with an estimated 5 million Muslims. France has a long, troubled relationship with its Arab immigrants and a more recent history of unrest among young native-born Muslims. There has been growing concern about young men and women returning to France after joining jihadist activity in the Middle East.