The attack on the Charlie Hebdo officies Wednesday lasted only a few minutes, according to witnesses.

Clad all in black with hoods and carrying assault rifles, the attackers forced one of the cartoonists arriving at the office building with her young daughter to open the door with a security code.

The staff was in an editorial meeting and the gunmen headed straight for the paper’s editor, Stephane Charbonnier – widely known by his pen name Charb – killing him and his police bodyguard first, said Christophe Crepin, a police union spokesman.

Minutes later, two men strolled out to a black car waiting below, calmly firing on a police officer, with one gunman shooting him in the head as he writhed on the ground, according to video and a man who watched in fear from his home across the street.

The witness, who refused to allow his name to be used because he was afraid for his safety, said the attackers were so methodical that he first mistook them for France’s elite anti-terrorism forces. Then they fired on the officer.

“They knew exactly what they had to do and exactly where to shoot. While one kept watch and checked that the traffic was good for them, the other one delivered the final coup de grace,” he said. “They ran back to the car. The moment they got in, the car drove off almost casually.”

The witness added: “I think they were extremely well-trained, and they knew exactly down to the centimter and even to the second what they had to do.”

While the attack appeared to have been orchestrated, not everyone was convinced that the attackers had professional training. The shooters, for example, at one point cross each other’s paths as they advance up the street – a type of movement that professional military personnel are trained to avoid as it would limit the ability of the shooters to maximize firepower.

“From what I’ve seen, their shooting stance and movement indicates they are not well trained,” Dan Rassachack, a Marine with training in close-combat skills, said in an email.

U.S. and Western security officials cautioned that they had not reached any conclusions about the affiliation of the three attackers, who killed 12 people in the assault, or determined whether they had any military training or had been to Syria to fight there.

– From news service reports