Mindhunter: Inside the FBI's Elite Serial Crime Unit (by John Edward Douglas, with Mark Olshaker)

I haven't seen the Jonathan Groff series based on this book (which, why haven't I) but this is a nonfiction book by John Douglas, whose work on criminal psychology is well-familiar to true crime fans: he came up with the distinction between organized and disorganized offenders, and the idea of the "signature" of the criminal.

This is a bit of a true crime classic, although it's slightly outdated and Douglas comes off as a bit arrogant about the accuracy of his profiles.  (I wish he'd included a an anecdote or two about a time that his analysis was way off. I'm sure those existed.) His pro-death penalty tangents are a bit didactic for my taste too. But overall, a gripping and spine-chilling read for true crime fans.