So, the culprit is a religious extremist going around killing spirits just for the sake of killing them? Or the stray mage in Nazru was killed by an extremist for cooperating with spirits, and someone else is trying to keep the mage's orphan spirit alive by hunting other spirits to feed to it. Perhaps the man with the small child visiting the mage was some abomination that could suck life and mana out of other people (like a vampire). The child might have been just a diversion, perhaps replaced by the mage's spirit afterwards. Or the child could have been the monster. Not enough info available yet.