I don't usually read true crime, although I have read In Cold Blood and Helter Skelter. However, I was in high school in the Chicago suburbs when the John Wayne Gacy story broke, and I had to read John Wayne Gacy: Defending a Monster by Sam L. Amirante and Danny Broderick.
I found the book totally engrossing, but I think that is partly due to the the timing and location of the trial when I was a teen-ager. I haven't read any other books about Gacy, so I learned a lot about the crimes, the man, and the trial.
Defending a Monster is not destined to become a classic. It is not as good as In Cold Blood and Helter Skelter. It's also not really a true crime book. It's more the story of the lawyer whose first client in private practice was an acquaintance who turned out to be one of the most notorious mass murderers of all time. It's also a passionate plea from that lawyer to uphold the Sixth Amendment and provide everyone, no matter the crime, to a fair trial and a serious defense.
If you enjoy reading true crime nonfiction, or have an interest in the Gacy case, you will probably find this book interesting.