Chérif and Saïd Kouachi
The late Cherif Kouachi and Said Kouachi are suspects in the deadly attack on the Charlie Hebdo office in Paris Jan. 7, 2015. Judicial Police of Paris/AFP-Getty Images

One of the two brothers wanted in the worst terror attack in decades in France, which killed 12 people Wednesday at the office of satirical weekly publication Charlie Hebdo, received terrorist training in 2011 from al Qaeda in Yemen, American officials told the New York Times on Thursday. It’s unclear whether the al Qaeda affiliate had directly ordered the attack in Paris, the Times reported.

Saïd Kouachi, 34, reportedly spent “a few months” training in tactics that echoed Wednesday’s military-style attack, in which at least two gunmen were able to infiltrate Charlie Hebdo offices, carry out the attack and then flee the scene. Both Kouachi brothers have been on America’s no-fly list for years and were in the U.S. database of known or suspected terrorists. Saïd's younger brother Chérif, 32, first came under scrutiny as a possible terrorist by French authorities a decade ago. French officials detained him in 2005 when he tried to leave for Syria and Iraq, a U.S. intelligence official told the New York Times on Thursday.

“They clearly knew how to use the weapons. They clearly had the right level of ammunitions, and they certainly were accurate in their firing. They were well equipped they had the right clothing and everything else,” Bob Milton, a retired commander of the London Metropolitan Police Service in the U.K. and now a counterterrorism professor at Bay Path University, told International Business Times Wednesday.

Witnesses claimed the gunmen who stormed the editorial offices declared their loyalty to al Qaeda in perfect French. Cédric Le Béchec told French news site that one of the men said, “You tell the media it was al Qaeda in Yemen.” Al Qaeda in the Arabian Peninsula (AQAP) is the group’s official Yemeni affiliate.

The Islamic State group, or ISIS, praised the attackers as “brave jihadists” during a radio broadcast Thursday. ISIS did not claim responsibility for the Charlie Hebdo attack, CNN reported.

A recent issue of the propaganda magazine published by al Qaeda in Yemen identified Charlie Hebdo’s chief editor, Stéphane Charbonnier, in a two-page spread titled “Yes We Can: A Bullet a Day Keeps the Infidel Away – Defend the Prophet Muhammad peace be upon” on a “wanted: dead or alive” list of Westerners who have insulted the Muslim faith, according to Jihad Watch.

“They’ve got the ambition and the proven capability of operating outside the peninsula,” Milton said of AQAP on Wednesday. But American officials said Thursday that there were indications the Kouachi brothers acted on direct orders from Yemen’s al Qaeda branch and that the investigation is ongoing, the Times reported.

A manhunt was underway Thursday in northern France’s Picardy region, where police reportedly spotted the two suspects on foot in a wooded area, according to CNN.

French President François Hollande yesterday declared Thursday a national day of mourning for the 12 victims of the Charlie Hebdo massacre. People across France observed a moment of silence at noon and the sparkling lights of Paris’ Eiffel Tower went black at 8 p.m. local time Thursday.