Yes, everyone who kills innocent people should be prosecuted and convicted.
That said, we cannot ignore the root cause of the killing. Killing in self-defense is permissible under some circumstances. But killing innocents because you believe that your god is the only true god, and killing those who do not believe in this god is lawful and morally right, is not right.
And the ideology which encourages this kind of violent belief among otherwise normal people should be questioned and criticised.
