This chapter considers professional development from the perspective of medical witnesses to identify the role played by specialist groups and the particular knowledge that they brought to bear on evolving forensic practices. The chapter first sets out the range and character of the criminal cases on which the book is based. It uses a series of tables and graphs to summarise the collected data, identifies trends over time and highlights comparisons between regions, medico-legal practices and the medical practitioners involved in crime investigation. In the absence of a centralised provision, legal officials such as coroners, magistrates and the police turned to the medical professionals who were closest to hand, especially local surgeons and GPs; a much smaller group of medico-legal witnesses worked at institutions such as hospitals, workhouses and prisons, or held an official appointment as a police surgeon, until now an under-studied area of medical practice.