I haven’t read it but I guess this book really goes into the speculation of what he really did
https://www.amazon.com/Beyond-Cruel-Chilling-Americas-Sadistic/dp/0312942516/ref=nodl_
Read about Michael Debardeleben.
Beyond Cruel: The Chilling True Story of America's Most Sadistic Killer
https://www.amazon.com/Beyond-Cruel-Chilling-Americas-Sadistic/dp/0312942516/ref=nodl_