A standout in the recent spate of books about serial killers. Here, the murderer is still at large, and the focus is on in-process police work and the laborious ponderings of the forensic psychologist trying to trap the butcherer of six women. Ginsburg (Poisoned Blood, 1987) describes ""the Valley""--a small section of New Hampshire and Vermont where, until recently, an older way of life was preserved: People left their houses unlocked and the keys in their ears. That ended in the early 80's, when the body of a murdered 13-year-old-girl was found. By 1983, when the killer was caught, he had struck twice more. During the investigation, psychologist John Philpin came forward and offered to help; for years, he had made a hobby of studying murderers. Philpin predicted that the Valley's serial slayer would be in his 20s, living with his mother, awkward with his peers, perhaps deeply involved in church, and would spend hours driving around looking for the right victim--and Philpin proved right on every point. But as soon as this serial killer was behind bars, Valley women began disappearing again--and so Philpin was called in to help. Here, Ginsburg is riveting as he gets down to the brass tacks of Philpin's method. The psychologist goes to the crime scene and identifies completely with the killer, imagining what kind of girl the killer would select, how he would stalk her, how he would beat and stab her, and how he would enjoy his crime. But in the new killings--six to date--the best efforts of Philpin, the state police, and FBI forensics have been to little avail. For in a crowning irony, Philpin and the cops are certain of the identity of the killer--a local resident--but can't gather enough evidence to indict him. Unusual for its psychological depth and close-ups of exotic new forensics.