This was no Helter Skelter, but a thoroughly mediocre account of Dennis Rader's life and crimes, bedeviled by typos and bad grammar. I nearly had a heart attack reading this sentence: "Two years later, he and Paula's first child, a son they named Brian..."
Anyone who writes a sentence like that should have his college degree rescinded. It's fine to use a pronoun, but it needs to be a possessive pronoun, the way "Paula's" is possessive. If you're not sure what a possessive pronoun is, separate the parts of the clause:
Paula's first child (sounds okay)
He first child (very caveman)
Separating the parts of the clause should inform your ear what pronoun works there. His!
If all that is too confusing, you can just simplify it and write "their first child."
So, BTK (Bind-Torture-Kill, Rader's name for himself in taunting letters he sent to the police over many years). There is a large omission in the book: the torture. It's not clear whether this is because there was no actual torture (no real torture is described when Singular describes the crimes), or because BTK simply did not admit to the torture. It's not clear why he would be shy about admitting torture, since he admitted to murders and all sorts of sexual perversions.
Singular spends lots of time talking to Rader's Lutheran pastor, a very decent man but a little strange himself (he liked to go up to strangers, especially women, and ask if they wanted to see his stool samples. If they didn't run away screaming, he brought out a small container labeled "Stool Sample" which contained a tiny, three-legged stool). Needless to say, Pastor Clark and the Lutheran congregation feel shocked, horrified, and betrayed that they unknowingly had a serial killer in their midst. Clark tries to come to terms with it by talking about evil and demonic possession, which hardly seems an adequate explanatory paradigm, but Singular gives him dozens and dozens of pages in which to do so. It was a relief to hear from some experts at the end of the book, a psychologist and a clinical social worker (Howard Brodsky and Joycee Kennedy) who opined on how Rader had sexual desires and perversions, dating from childhood, which could probably have been channeled into non-murderous pursuits between consenting adults such as S&M and bondage clubs. (Presumably the impulse to strangle animals, which Rader also had and acted on, can be rechanneled somehow?) But since Rader had been brought up to be good, moral, and Christian, married to a Christian woman, with two Christian children, was a Boy Scout leader and President of his church, there was no socially acceptable outlet for his perverse impulses, so he hid them and they emerged in the form of stalking, binding, and strangling women, then photographing their dead bodies, sometimes with masks on. (His victims also included an adult male and a boy who happened to be home when he was attacking a woman.) Our language for talking about crimes like these is steeped in metaphor, Kennedy says. Not just evildoers, or bad people, but narcissistic personality disorder, antisocial disorders: these are just metaphoric labels for neurobiological problems - mental illness. Our criminal justice system is completely archaic on the subject of mental illness, she argues. Killers like Rader are mentally ill, but not in the way that the courts use that term. They're aware of the wrongness of their actions, but the way their brains are wired - their "impaired sensory-emotional integration" - is providing the impetus for their crimes.