The Killer of Little Shepherds, By Douglas Star

The French detectives who gave us CSI

In the artificial light, the blood stains show up brightly.

Forming a spattered pattern on the fabric, they reveal to the investigator exactly how the victim was dispatched. The police photographer moves in to set up his camera, carefully measuring out his shots. Later, back in the morgue, using up-to-the-minute techniques, a post mortem examination is performed.

So far, so episode of the TV drama CSI. But this crime scene investigation doesn't take place in modern Manhattan but fin-de-siècle France. Douglas Star's book charts the gruesome crimes of a man dubbed "the French Ripper", Joseph Vacher, who murdered, mutilated and sexually assaulted 11 people in the rural south-east of France. But this is more than just a true-crime blockbuster with a historical edge; it is an account of the dramatic birth of forensic science, and a memorial not to a serial killer but to the pioneering men who caught him.

A failed priest and ex-soldier, Vacher was sent to an asylum after attempting to kill a young woman who rejected him. But he convinced the authorities he was cured, took to the countryside as a vagabond, and soon began his murderous spree.

Interspersed with his bloody progress is the story of Dr Alexandre Lacassagne, the true hero of Star's book: a larger-than-life character whose all-questioning approach to criminology, autopsy and mental illness is still relevant to criminal investigations to this day. Given that his was an age when rural post mortems often took place outside and in all weathers, when the refrigeration of corpses was barely known, and when Lyon's morgue was located on a wooden barge which would disgorge its gruesome cargo during storms or flooding, Lacassagne's forensic innovations, from collecting fibres to tests to show up blood and semen, were remarkable.

More remarkable still was Vacher's court case, thanks to the brilliance of another man, the prosecutor Emile Fourquet, and his ability to see a pattern in Vacher's crimes and extract a confession. One of the great debates of the day then stood between Vacher and the guillotine: could a man who had committed such crimes be sane? If not, he should not be executed, and it fell to Lacassagne to prove beyond doubt either way. He argued that Vacher was indeed of sound mind and the jury agreed, although some of the best-known doctors, judges and writers of the day were deeply divided over what many believed to be a miscarriage of justice.

Star has created a book with every bit as much tension as a thriller, as much detail as a meticulous police procedural, and a court-room drama that's up there with the best. Furthermore, much of what occurred in 1890s France still has meaning today, and techniques developed then led to the procedures we use today. Lacassagne called for the government to set up a nationwide agency to collect data on crime; almost half a century later, Interpol came into being.

"CSI Belle Epoque"? It's not as crazy as it sounds.