They were trying to get into the building.
"We heard the first shots and then more and more shots, right across the whole five or six minutes." And they heard screams, said Boudot, who is a documentarian.
They ran for the roof, while their minds raced through possible dangers.
"We knew that there were victims
a few meters away from us, but there might be, you know, some explosives somewhere or maybe a third guy," Boudot said.
Separating men from women
In the offices of Charlie Hebdo, the masked gunmen
dressed in black apparently barged in on a conference. Survivors later told their stories to a doctor who treated them. He relayed them to CNN.
The gunman separated the men from the women and called out names of cartoonists. Then they fired. Not randomly spraying bullets, but taking professional, precise aim.
They left the building, and cell phone video captured them as they ran in the street and kept firing. One of the masked men ran over to a man in uniform lying apparently wounded on the sidewalk and shot him at close range.
The two said they were avenging the Prophet Mohammed and shouted "Allahu akbar," which translates to "God is great," a French official said.
Video shows a gunman approaching his black getaway car and raising his finger. Perhaps it was a signal.
A coveted target
When the gunfire ceased, Boudot and his colleagues went back into the building.
They couldn't have been too surprised that the satire magazine had been attacked. Threats against it had been widely reported.
Charlie Hebdo's previous offices had been fire-bombed three years before, the day it was to publish a provocative cover lampooning the Muslim prophet Mohammed.
They moved to their current office a year ago, Paul Moreira, who works in the building, told CNN's Erin Burnett.
The magazine refused to change anything and kept publishing irreverent cartoons on Islam but also on Christianity, Judaism, politics and society -- in its usual profane style.
Charlie Hebdo's editor, cartoonist Stephane Charbonnier -- "Charb" for short -- was on an al Qaeda target list. The gunmen killed him, as they did three other famous cartoonists, known by the pen names Cabu, Wolinski and Tignous.
Charb was constantly guarded, Dutch journalist Stefan de Vries told CNN's Don Lemon.
"He was always accompanied by one or two secret service officers. Everywhere we went, for the last four years. At day and at night, so he was protected," he said.
De Vries thinks one of those killed was a body guard.
Bodies on the left
In the meeting room, Boudot saw bodies lying off to the left. Survivors were either hiding or standing.
"They were just standing like -- not zombies -- but they were standing and didn't do anything," he said. "We tried to help the very first one, but actually, to be honest, there were not a lot of wounded, they were just people dead, all around."
But the gunman had not only killed in the meeting room.
Moreira made his way to Charlie Hebdo's offices as well. The first thing he saw was the body of a building doorman. "This grumpy guy we liked and appreciated. He was lying down in his blood, and he was dead; he had been shot by the gunners."
Blood stained the stairways, where heavily wounded people lay. A man Moreira knew for 20 years had been shot in each leg. Moreira went up to the cartoonists' offices.
Witnesses huddled with survivors. "They were in one room, some crying hysterical. Some were, like, prostrated and not capable of saying anything, saying a word," Moreira said.
The gunmen had shot dead eight of their colleagues, as well as a guest, the doorman and two police officers.
On Thursday, businesses around the corner in the trendy inner city neighborhood reopened, cafes filled with patrons and traffic congested streets.
Aside from a covey of journalists' satellite trucks the only sign of the carnage a day earlier was a tribute taped to a tree.
A bouquet of roses and a quote by a French philosopher.
It read, "There is only one step from fanaticism to barbarism."