With your username I'm surprised you think that atheism plays a role or is somehow a prerequisite.
Its merely the believe that there's no god.
This action is just as likely to be done by anyone not caring for the Catholic church, which includes (among others) agnostics, Muslims, hindi, christians that don't believe in hell, christians that want to be evil, etc.
It's safe to say that the person in question was a psychopath though. Nobody with healthy empathy could do this.