The worst terror attack in decades in France, which killed 12 on Wednesday, was well planned and executed by highly trained operatives. Three gunmen stormed the office of satirical newspaper Charlie Hebdo and killed 10 journalists and two police officers before escaping. Several reports tied the gunmen to al Qaeda, and though their allegiance has yet to be confirmed, the attack does bear the terror group’s trademarks.

Al Qaeda, unlike the Islamic State group, has the capacity to carry out such a large-scale massacre in the West and, in the past, has provided attackers with training, intelligence and weapons. The gunmen’s ability to both infiltrate the building and flee the scene suggest that they were professionally trained and had been planning the attack for some time, unlike the recent “lone-wolf”-style attacks from terrorist sympathizers in the West.

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,” said Bob Milton, a retired commander of the London Metropolitan Police Service in the U.K. and now a counterterrorism professor at Bay Path University. “To me, it’s all the hallmarks of people who had actually been fighting. It may very well turn out that these three have actually been to Afghanistan, been to Iraq, been to Syria and have actually been involved in some fighting already.”

It is still unknown where the gunmen received their training, but at least two eyewitness testimonies claimed the gunmen declared their allegiance to al Qaeda in perfect French. Cedric Garnier told French news site that one of the attackers said, “You tell the media it was al Qaeda in Yemen.” Al Qaeda in the Arabian Peninsula (AQAP), is the terror group’s official Yemeni branch.

“Al Qaeda, without a doubt, are the professionals. Whether it's to al Qaeda core or whether its al Qaeda in the Arabian Peninsula, time will tell,” Milton said. “I wouldn’t be at all surprised if it was AQAP, particularly in Yemen, because they've got the ambition and the proven capability of operating outside the peninsula.”

“There are a lot of rumors out there,” State Department Spokesperson Jen Psaki said when asked about the gunmen’s links to AQAP in a press briefing. “But I don't want to speculate on that at this time.”

Though the Islamic State group’s swift rise to power and declaration of a so-called caliphate has stolen the jihadi spotlight, al Qaeda central is the group behind the largest terrorist attacks in the West. AQAP is one of the largest branches and considered to be the more dangerous direct threat to the United States. AQAP has recently stepped up its online presence to regain its position of power in the terrorist hierarchy. The group released a video of its “first international press conference," and answered questions from journalists via social media, last month.

Despite AQAP’s desire for international attention online, on the ground its direct enemy is still the Yemeni security forces, making it unlikely that the group would use its resources in France, according to Peter Knoope, an associate fellow at International Center for Counter-Terrorism, an independent think tank in The Hague.

“Why all of a sudden would they come to Paris and attack … putting the international attention on them?” Knoope said. “I can't see the reasoning. You’re there in Sanaa and all of sudden you think let's attack something in Paris to do with cartoons? It seems not very logical.”

However, al Qaeda central’s enemies are not as local as the Yemeni branch’s, and Charlie Hebdo was one of the terror group’s targets. A series of satirical cartoons of the Prophet Muhammad published in 2007 resulted in direct threats from al Qaeda central.  In 2013, the newspaper’s editor in chief and cartoonist Stéphane Charbonnier, known as Charb, was listed in an article titled "Wanted Dead or Alive for Crimes Against Islam" published in al Qaeda’s Inspire Magazine, according to the Telegraph. Charbonnier was one of the 12 killed in Wednesday’s attack.

“If it is true, it is a very significant move,” Milton said. “It’s another step forward for the ambitions of al Qaeda in the Arabian Peninsula and should be taken very seriously.”