I promise this isn't as weird as it sounds. I've tried a bit of Googling but I can't find anything that works well.
I'm looking for a single word for a pyromaniac that burns people alive. The question, What is the Single Word for Burning Alive? it told me about the word "immolation" which is the verb for burning people alive (usually in ritual sacrifices). But I can't find a noun for the person who does it. I would also be fine with some kind of religious term for the priest who performs a burning sacrifice. If all else fails, it can be the person who sacrifices animals if there isn't a word for people.