Cartoonist Corinne Rey said she was the one who let two gunmen into the office of satirical magazine Charlie Hebdo where she worked as she and her young child were "brutally threatened".
Ms Rey, whose pen name is Coco, had just picked up her child from nursery on Wednesday and was going to enter her office building when she was confronted by two heavily armed men wearing balaclavas.
"Two masked and armed men brutally threatened us... They wanted to get inside, go upstairs. I tapped in the entrance code," the 32-year-old told the French media.
"They spoke perfect French. They said they were from Al Qaeda," she added.
Terrified, Ms Rey and her daughter hid under a desk, and witnessed two other cartoonists being executed.
"They shot Wolinski and Cabu. It lasted five minutes," she said.
Mr Geoges Wolnski, 80, and Mr Jean Cabut, aka Cabu, 76, were two of her fellow cartoonists who were killed in the massacre. Others included two policemen, chief editor Stéphane Charbonnier, aka Charb, 47 and Mr Bernard Verlhac, aka Tignous, 58. The gunmen had reportedly asked for names before shooting. Ten people were killed in the building, in addition to a policeman who was patrolling the streets and a maintenance worker at the next building.
Ms Rey was not the only eyewitness to the horrific incident. The Guardian reported that tweets by Mr Yves Cresson, who works for media production company Bayoo next door to Charlie Hebdo showed that the two attackers initially walked into his office.
At 11.25am, he tweeted (see below): "Taking advantage of the postwoman, two armed men wearing balaclavas entered our offices."
He subsequently tweeted that they were looking for Charlie Hebdo, and left after firing two shots to his office window and door.
"They fired two shots to the door, and to the window."
"We came to find one bullet in our office."
As of Friday morning, the gunmen were still at large.
The French magazine first came to international attention in 2006, when its decision to reprint a selection of cartoons depicting the prophet Muhammad, first published in the Danish newspaper Jyllands-Posten, sparked outrage across the Muslim world.