The penal code of 1810 found the judiciary institutions on the affirmation of individual free will. Crime is conceived as a conscious choice made by a rational individual. Opposed to this view of a rational criminal is the traditional concept of madness, which sees mad people as not conscious. In the first half of the 19th century, emerging psychiatry proposed a new concept of madness which was compatible with consciousness. Therefore, the image of a criminal freely choosing his act was confronted with the new idea of a possible madman whose will has been altered. This paper proposes to analyze the confrontation of justice and psychiatry through the study of forensic expert valuations. Undeniably, the amount of forensic reports is increasing, indicating the growing doubt about the nature of the criminal act among the community of magistrates. Nevertheless, the magnitude of the medical influence should not be overestimated. Although the legal institutions seemed to be confused at first, control procedures were established, eliminating the most subversive representatives of the new movement. It was finally the elaboration of psychiatric theories that allowed for a more settled-down expertise. By shifting towards organicism, the roles between judges and medical doctors were clearly established. Medical experts strictly limited their reports to the study of the body, while the expertise of the soul and motivations was the responsibility of the judges. The traditional view of madness could therefore be maintained without having to abandon the foundations of the legal system.