I’m posting from memory [probably not a great idea] but I recall reading this about the CH security. It was quite good, with coded locks, etc. However, the attackers told one of the women they would kill her child if she didn’t let them in. She felt she had no choice.
Here is a link:
‘Charlie Hebdo cartoonist spoke of how she was forced to let the gunmen who massacred her colleagues into the satirical magazine’s office after they threatened to kill her daughter. Corinne Rey, who draws under the name Cora, was on her way into work with the toddler when men armed with Kalashnikovs demanded she take them inside.
“I had gone to collect my daughter from nursery and as I arrived in front of the door of the paper’s building two hooded and armed men threatened us,” she told French newspaper L’Humanite.
“They wanted to go inside, to go upstairs. I entered the code.” The attackers killed a security guard in reception before going upstairs straight to the newsroom on the second floor, where they reportedly called the names of cartoonists before opening fire in an editorial meeting.’