In order to read Maury Terry's book The Ultimate Evil we need to talk about the word "satanic." It's a messy topic but an important distinction to make when we talk about true crime books that dip into the idea of satanic cults as this one does with the Son of Sam killings.
The distinction is nudged at by Joshua Zeman in his excellent introduction to the reissue of the book, and I go as deep as I can on it.
Dispatches From Creative Isolation: Changing My Mind By Dissecting My Mind
The Satanic Panic and the Religious Battle for the Imagination
Satanic Confusion: The Distinction of Words