A slightly different one but The Last Victim by Jason Moss has haunted me for years.
Summary from Wikipedia-
In 1994, Moss was an 18-year-old college student at UNLV. While studying for his honors thesis, he established relationships by correspondence with John Wayne Gacy, Richard Ramirez, Henry Lee Lucas, Jeffrey Dahmer, Elmer Wayne Henley, and Charles Manson. He obtained samples of correspondence from and interviews with these men. Moss researched what would most interest each subject, and cast himself in the role of disciple, admirer, surrogate, or potential victim.
In his book Moss said that he had been interested in a career with the FBI. He thought that gaining the trust of a serial killer, possibly learning more about their stated crimes or unsolved murders, was a way to distinguish himself as a job candidate.[1]
Moss claims to have forged the strongest relationship with Gacy; their letters led to regular Sunday morning phone calls, during which Gacy reiterated his innocence even as he gave Moss a guided tour of his world. In the book, Moss recounts his correspondence and eventual two meetings with Gacy about two months before the killer was executed. Moss believed that he became Gacy's "last victim" after this face-to-face meeting in prison, in essence being psychologically overpowered by the manipulative, depraved sociopath whom he claims prison officials left him alone and unsupervised with for two consecutive days and in which he alleges Gacy repeatedly threatened to rape and murder him while alone in his presence. For a time he suffered nightmares from the encounter.[2] Moss felt that this misadventure allowed him to understand how a killer's mind works in controlling the vulnerable and forcing them to submission.
It really got under my skin, especially parts where Gacy honed in on Moss’ relationship with his younger brother.
I’ve never know anyone else who’s read it, which is a shame as I’d love to chat about it!
I always thought it’d make an amazing Netflix documentary. It was made into a fairly low-budget tv movie at one stage (I haven’t seen it). The author died by suicide about 7 years after it was published, and it’s very hard to get hold of a copy now (even on Amazon- it’s only on Audible) so I’m guessing the family wanted to let this awful story die with him.