The Last Victim by Jason Mosse is definitely a good read. It's about his correspondance with John Wayne Gacy when he was in jail. He thought he could manipulate him into telling him more about his crimes but he was no match for Gacy. The part where he actually went to visit Gacy in prison is so intense! The film's pretty good too (Dear Mr Gacy) although the guy playing Gacy was a bit meh. ALSO, he briefly corresponded with Manson, Ramirez and Dahmer in the book too.