This is a serious account documenting the ascent of forensic science in the late 19th century, set against the background of the story of a notorious French serial killer, Joseph Vacher.
I was initially turned against it by its lurid cover (culled from the French “red tops” of the day), but the further I read into it, the more interesting I found it. Most of the first half is taken up with the tale of Joseph Vacher and his appalling crimes, which are truly stomach-churning, particularly as all the victims were completely innocent. This is interspersed with the introduction of scientists and lawyers of the period who were actively pioneering new methods of crime investigation.
The real story is that of two men, without whom Joseph Vacher would never have been apprehended. Its hero is undoubtedly Alexandre Lacassagne, head of the Institute of Legal Medicine in Lyon. He was one of the first people to recognise that a murder could be solved by examining the body of the victim. But his convincing medical evidence could not have been produced without the impetus provided by Emile Fourquet, a magistrate, who in 1899 began to make a study of vagabonds – homeless men who were forever on the move, earning a crust here and there. From this he began to understand that the small departments into which the French legal system was divided hindered investigations. Vacher had committed numerous horrific murders in disparate areas of France, always moving on rapidly afterwards... Fourquet gathered information about serious crimes and looked for patterns in the way they had been committed.
When Vacher was finally brought to book he admitted to the murders but claimed he was innocent because he was insane at the time . Lacassagne was convinced he was not insane (although he had spent periods in asylums). The case went to appeal on that basis, with other medical witnesses being equally convinced that Vacher was insane and should therefore escape the death penalty.
In the final sections Douglas Starr points out that there is still no way to prove beyond doubt that a criminal is actually insane.
This is an interesting book, which might well be useful to potential crime novelists. I would have liked even more from the perspective of Lacassagne and Fourquet.