I heartily recommend The Monster of Florence by Douglas Preston and Mario Spezi. It's about a series of unsolved murders in Italy in the 80's that are assumed to be by the same individual. The two authors investigate and uncover new information, experience a very unsettling coversation with someone that was never investigated by the police but who they think may have been the Monster. And Mario Spezi, the co-author, is actually arrested and accused of being the Monster!
This book is absolutely riveting and extremely creepy, and the story of all of the suspects that were accused at one point or another, police corruption and incompetence, and the whole sequence of events that occurred over the years is truly mindblowing.
Hope I didn't oversell it, but it is great true crime!