"At first, we just heard shots. We heard screams," he told CNN's Anderson Cooper.
Boudot and his colleagues made a mad dash for the roof. They didn't know what to do.
"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.
They made their way to the offices of the satirical magazine once the shooting stopped.
"It was a slaughter. It was like a massacre," said Boudot.
He saw the bodies of those killed in a meeting room.
In total, 12 people were shot dead in Wednesday's attack, including a building worker, two police officers, eight journalists and a guest of the magazine.
Those who survived were shell-shocked.
"They were just standing like, not zombies, but you know they were like standing and they didn't do anything," Boudot said.
The journalist described the gunmen as professional, people who knew their way around weapons.
It was a sentiment echoed by a doctor who helped treat the wounded and spoke with survivors of the attack.
Dr. Gerald Kierzek said the gunmen divided the men from the women before opening fire.
The shooting was not a random spray of bullets, he said, but more of a precision execution.
The gunmen asked for specific people by name before killing them, the doctor said.
French police were still looking for at least two suspects Wednesday night: Cherif Kouachi and Said Kouachi. Both are potentially armed and dangerous.
Citing sources, the Agence France Presse news agency reported that a third suspect had surrendered to police. CNN has not independently confirmed whether that is true.
Paul Moreira, another witness to the attack, knew many of the victims.
"The stairways were full of blood, and I saw heavily injured people," he told CNN's "Erin Burnett OutFront," including a friend he's known for more than 20 years who was shot in the legs.
He also saw the doorman.
"The man that I would see every morning -- this grumpy guy that we liked and appreciated -- he was lying down in his blood. He was dead.
"They (the gunmen) wanted to go inside as quick as possible. He wasn't fast enough to open the door of the building and they shot him," Moreira said.