According to a Swedish/French journalist who had been working with some of the victims the cartoonist did not usually spend their time at the Charlie Hebdo office, but convened there for editorial meetings only.
Were the terrorists lucky or did they know?
Anyway, their luck may soon have run out. According to a French newspaper the police have identified them......
Even if they arrest the murderers, I would not doubt they get to dictate conditions at trial and get a slap on the wrist.
French Police are known for being mean, but who knows, maybe the culprits will commit suicide upon being accosted.
It does seem as if they must have known about the editorial meeting. They also had a sort of priority list of names, and asked people to identify themselves and then shot them. So they must have been expecting to find all those people there.