At the end of the nineteenth century, serial murderer Joseph Vacher, known and feared as "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--intelligent and bold--typified the Belle Epoque, a period of immense scientific achievement and fascination with science's promise to reveal the secrets of the human condition. With high drama and stunning detail, Douglas Starr revisits Vacher's infamous crime wave, interweaving the story of how Lacassagne and his colleagues were developing forensic science as we know it. We see one of the earliest uses of criminal profiling, as Fourquet painstakingly collects eyewitness accounts and constructs a map of Vacher's crimes. We follow the tense and exciting events leading to the murderer's arrest. And we witness the twists and turns of the trial, celebrated in its day. In an attempt to disprove Vacher's defense by reason of insanity, Fourquet recruits Lacassagne, who in the previous decades had revolutionized criminal science by refining the use of blood-spatter evidence, systematizing the autopsy, and doing groundbreaking research in psychology. Lacassagne's efforts lead to a gripping courtroom denouement. "The Killer of Little Shepherds" is an important contribution to the history of criminal justice, impressively researched and thrillingly told.