Anyone care to share where the idea of your victims in this life become slaves in the next came from? I'm curious about that and I remember that idea was also shared by one US killer that massacred at an elementary school.
https://www.brutenorse.com/blog/2018/4/17/an-old-norse-word-...
I'd also wager that the battlefield scenario that the Viking belief was developed around would simply divide everyone into "allies" and "enemies." So a killer who sees himself as following that logic would apply the same black and white logic, their victims being enemies in some personal war.
I've also read some theories about Zodiac in particular that he might not have genuinely believed in that storyline either, that he was just taunting the public. Whether he believed it or not I guess we cannot know, but I would still say based on his actions he wasn't the most reasonable person on the planet.