Youngest Suspect in Charlie Hebdo Attack Turns Himself In, 2 Others Sought Gunmen shot victims "execution style" one by one, Paris deputy mayor says.

 -- The youngest suspect in today's deadly attack at a satirical newspaper's office in Paris has turned himself in, French police said, while the other two are “on the loose, armed and dangerous."

French authorities have named the three suspects who they believe are responsible for the shooting deaths of 12 people, U.S. law enforcement officials told ABC News.

Officials identified the suspects as Said Kouachi and Cherif Kouachi, two relatives both in their 30s and still at large, and 18-year-old Hamyd Mourad, who police say is cooperating after his surrender in the French town of Charleville-Mezieres, about 140 miles north of Paris.

Cherif Kouachi, 34, is listed in a private database, ABC News has confirmed.

Kouachi, along with six others, was sentenced in May 2008 to 3 years in prison for terrorism in Paris. All seven men were accused of sending about a dozen young Frenchmen to join Abu Musab al-Zarqawi, the leader of Al Qaeda in Iraq, after funneling them through radical religious establishments in Syria and Egypt. French authorities believed Kouachi had been planning to go to Syria for training in 2005.

Paris Deputy Mayor Patrick Klugman earlier today told ABC News that two of the assailants went inside the offices of Charlie Hebdo and listed off the names of their targets before shooting them execution style. The third man was waiting outside the building.

The French president called the attack a "terrorist operation."

The shooting at the office of Charlie Hebdo was a "cowardly attack," said President Francois Hollande when he was at the scene this morning.

"This is a terrorist operation against an office that has been threatened several times, which is why it was protected," he said, without going into the specifics of the police protection at the office in the center of Paris. Photos from the scene show a police car riddled with bullet holes.

The newspaper had been targeted in the past over its content, often aimed at religious groups.

French officials confirmed that there are believed to be three attackers, all of whom were seen in videos wearing black from head-to-toe. Their identities and affiliations have not been revealed but one of the men is heard screaming "Allahu Akbar," an Islamic phrase meaning "God is great," in one of the scene videos.

This morning's turmoil punctured an otherwise normal day in the French capital, with the gunshots audible from nearby buildings, sending bystanders cowering. The masked gunmen were later seen fleeing the scene and hijacked a car, authorities said. They have not been caught and a search is underway for the shooters.

The tragedy marks France's deadliest terror attack in decades. The government raised its terror alert to the highest level and reinforced security at houses of worship, stores, media offices and transportation.

The New York City Police Department ordered extra security to the French consulate in Manhattan and the U.S. Department of Homeland Security said that they are closely monitoring the events in France and are ready to adjust their "security posture, as appropriate."

Charlie Hebdo, a satirical newspaper, has come under attack before. Their office was firebombed in 2011 and its website was hacked after its cover featured the prophet Muhammad. Nearly a year later, the publication again published crude Muhammad caricatures, drawing denunciations from around the Muslim world.

The cover of this week's issue of the newspaper focuses on a new book by Michel Houellebecq, “Submission,” which depicts France led by an Islamic party that bans women from the workplace.

President Obama condemned the "outrageous" attack.

"France is America’s oldest ally, and has stood shoulder to shoulder with the United States in the fight against terrorists who threaten our shared security and the world," President Obama's statement read. "Time and again, the French people have stood up for the universal values that generations of our people have defended."

Canadian Prime Minister Stephen Harper expressed sadness following the shooting.

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