I gave a talk last night to Dr. Tali Walters’ class on forensic psychology at Tufts University. Dr. Walters is an eminent forensic psychologist who has interviewed some of the most notorious serial killers of our time. She asked me to describe Joseph Vacher, the villain in my book, talk about his crimes and see what diagnosis the students came up with. Almost to a person they decided that he was legally sane and fit to stand trial. In doing so they agreed with the diagnosis of almost every other serial killer, whether in past times or present — that the act takes such cunning and planning that the perpetrators must be legally sane.