My main concern with the Franks is that it relied heavily on
propensity reasoning, which can lead to a form of logical fallacy
These kinds of inferences can be a powerful investigative tool i.e profiling. This crime scene has occult/pagan staging. Odinism is a type of paganism. These people are Odinists. Therefore maybe these people did it. It enables you to winnow down a target list of people where you can look for actual evidence.
However there is a risk of logical fallacy here. IMO much of what is in the Franks is propensity reasoning. IMO the Facebook posts about sticks and runes are not evidence of a crime, but evidence of disposition, that allegedly makes it more likely these people are the real killers. But that is quite some assumption - first perhaps Turcow will say he can't even conclude the crime scene does have odinist staging. Second, just because someone likes Odinism doesn't mean they want to do a murder. It's a huge leap.
It's interesting to contrast with KAK in that regard. If your theory is sexual motivation - then you have a suspect who is actually connected to the victim in the context of a catfishing crime. That to me is much stronger because you have a real evidential link between suspect and victim, not just disposition/propensity.
But KAK also illustrates the dangers of propensity reasoning. KAK did this other crime, therefore he must have done the murders. "It's too much of a coincidence". That road can lead to fallacy.
MOO