At the end of the nineteenth century, serial murderer Joseph Vacher, dubbed The Killer of Little Shepherds, terrorized the French countryside. He eluded authorities for years-until he ran up against prosecutor Emile Fourquet and Dr. Alexandre Lacassagne, the era's most renowned criminologist. The two men typified the Belle Epoque, a period of immense scientific achievement and fascination with its promise to reveal the secrets of the human condition. With high drama and stunning detail, Douglas Starr recounts the infamous crime and punishment of Vacher, interweaving the story of how Lacassagne and his colleagues developed forensics as we know it. We see one of the earliest uses of criminal profiling, as Fourquet painstakingly collects eyewitness accounts, leading to Vacher's arrest. And we see the twists and turns of the celebrated trial: to disprove Vacher's defense by reason of insanity, Fourquet recruits Lacassagne, who had revolutionized criminal science: refining the use of blood spatter evidence, systematizing the autopsy and doing ground-breaking research in psychology. Lacassagne's forensic investigation ranks among the greatest of all time, and its denouement is gripping. An important contribution to the history of medicine and criminal justice, impressively researched and thrillingly told.