So there's a book I recommend that's not a great BOOK (like stylistically), but which poses a REALLY fascinating theory regarding, among other things, the Villisca Axe Murders. I've reread it and skipped around because the information is good, but it's just not presented in the best way (IMHO). The book is The Man from the Train (https://www.amazon.com/dp/1476796262/ref=cm_sw_r_cp_apa_glc_fabc_PH8MYG5MTJERXSHPYX4P) by Bill James and Rachel McCarthy James.
It's definitely sent me down a LOT of really cool old rabbit holes, and if nothing else you can use it as a jumping off point for other Villisca theories.
Is it this one? https://www.amazon.com/Man-Train-Discovering-Americas-Elusive/dp/1476796262
That looks really interesting, I'll add it to my queue!