Honestly, the safe bet is always that they had a prior relationship, it’s usually spouse but in this case my money is on the killer also having nazi tattoos and this is somehow related to their little local chapter of whatever dumb org they probably belong to. Something along the lines of he was suspected of being an FBI informant or some such thing, or drug dealing related, those groups move a ton of meth.

Or he did some shit to someone and they did some shit back. But my bet is it’s just nazi on nazi crime.