Looking at his big thread, there are a lot of small circumstantial facts that he thinks adds up. That may be, but it's very hard to judge if confirmation bias/multiple comparisons is at play.

The most serious claims mostly rely on the daughters' recollection. However, if they can be independently verified, I'd say the case is pretty strong:

* The daughter says he abused her over her dating and drug use. If her recollection can be trusted, that was on the same day as the first murders.

* The father wrote a letter to a zine in response to a guy whose daughter had been exposed to drugs, where he claims that he was in a similar situation once and that some people are no longer alive because of it. He asked the editor of the zine to not print that part, too (He still did). This part doesn't rely on the daughter's memory.

* Putting those two together, it does look an awful lot like he might have been about to kill his daughter, then changed his mind and went out to "get revenge" on some random youths who he felt were the sort responsible for corrupting his daughter instead.

I think this is the strongest part of the evidence, so I'd like to see the true crime nerds engage with that, rather than, say, with the suggestion that he got his symbol from the minutemen group, or any of the more speculative stuff.

Also, there's the bloody fingerprint stuff. It hasn't been checked for this guy yet, but it has apparently been checked and found not to match for the other candidates the true crime nerds have launched over the years; based on that I'd say this one is, presently, at least as good a candidate as those.