He's probably going to use it as an excuse to suppress his Lepeniste enemies, even though they had nothing to do with it. They were pretty careful to call for the suppression of "hate" in general, not Al-Qaeda or anything that has to do with this gunman in particular. Maybe this doesn't translate well but in English, "hate" is a term of abuse for right-wing attitudes.
In this case though, Sarko should 'just' have banned muslim propaganda, since the perp was muslim.