They did not.

Charlie Hebdo did not publish, then get attacked for, content they themselves found offensive.

No, they know it's offensive and their fight was exactly about freedom of speech.

Yes, they knew it was offensive - to others. There is no indication that it actually offended them. Which, unless it did, it's not the same thing.

They are caricaturists, nothing can offend them. You miss the point of their reasoning.

Someone actually got arrested and went to jail in France for an offensive parody of one of the equally offensive Charlie Hebdo covers: https://electronicintifada.net/blogs/ali-abunimah/france-beg... (because it was insensitive to French people rather than Egyptians).

That's not entirely fair, either. I'm sure there are plenty of things that would offend them, but they understand that just because something is offensive does not make it wrong.

> nothing can offend them

Then they didn't die to protect speech they were offended by. I don't know how much clearer this can be.

It's not required to be offended personally by something to protect freedom of speech, I can understand how else I should say it. And if you don't want to understand it - Charlie Hebdo also published caricatures about christian religion, so it was offensive for them too, for their friends. Muslims just were more aggressive.

Splitting hairs doesn't make them any easier to find.

They did publish the original danish cartoons, which they publicaly said they found not from a very good taste, and that some were pretty bad cartoons, but that they had to publish them for the sake of free speech, even if it made them a target ( which it did). That's how it all started.