This chapter examines the active role of medical practitioners in crime scene investigation as a means of studying the evolution and bifurcation of the relationship between forensic medicine and forensic science in relation to the changing role of the expert, “one whose special knowledge or skill causes him to be regarded as an authority.” The first section examines the relationship by using pictorial depictions of crime scenes as a means of identifying the issues that investigators thought most relevant. The chapter then considers the use of scientific aids to investigation, mainly microscopic and chemical tests on blood and semen stains. Though not common in Victorian forensic practice, they help to identify a growing distinction between forensic medicine and forensic science, and between the expert and the expert witness. Finally, professional standing, experience and connections all affected income-earning potential, and so the last section considers the fees paid to medical experts to show how and why they held a different status to lay witnesses and how a minority transformed themselves into expert witnesses to be consulted in ‘special cases’ considered too complicated for the average practitioner.