The truth could be that this had nothing to do with the Hebdo event. The truth could also be that the commissioner was shot by a pro-Muslim group or by their benefactor the Socialist government because he was about to disclose evidence embarrassing to the Muslims or to the Socialists.
Who knows?
The police union says that he was depressed, but it seems odd for someone who was exhibiting signs of depression to have such an important job. He took the position over from someone who also committed suicide only a year or so ago.
Maybe he felt responsible for the lack of police firepower around the cartoonists, who were known jihadi targets.