I can recommend "an hour to kill" about the murder carried out by Ken Register and "death sentence" about the mass murder carried out by John List.

Also, pretty much you have gotten your hands on it by now, but if not: Mindhunter by John Douglas. The Netflix Series was based on it, but the book is so much more extensive and very interesting.

My wife said that "I'll be gone into the dark" by Michelle McNamara is very good, however I started it and could not get past it. I hated the fact that instead of sticking to the facts and to the subject matter, a lot of it is about "oh I'm Michelle McNamara and look at how interesting it is how I got into true Crime". For fuck's sake, we don't care about that!

https://www.amazon.com/Hour-Kill-Murder-Justice-Southern/dp/1250025850

https://www.amazon.de/Death-Sentence-Inside-Murders-English-ebook/dp/B01N49MVOF