This article seeks to study the work of forensic doctors who undertake examinations at the request of the public prosecutor, either in the context of investigations into cause of death or as part of inquiries into acts of violence. The article analyses the process by which the “white coats” of the hospital and the “black robes” of the public prosecutor’s office exchange information at the interface between the medical expertise of forensic doctors, the investigative work of the police and the legal process of establishing guilt. The article will demonstrate that, in a context of ever faster sentencing, magistrates and public prosecutors often see their professional autonomy being eroded by forensic reports, which come to define the range of choices available in terms of sentencing. The challenge to the autonomy of judges posed by the current trend towards automating judicial decisions is considered in relation to local configurations that regulate the relationship between judges and experts. The meso-sociological approach of this paper makes an important contribution to the literature through studying the social conditions under which scientific and legal expertise come to interact.