There is a considerable history of using calcareous microfossils in criminal investigations, and cases all fall into the provenance category. These are cases in which sediments containing calcareous microfossils are associated with a crime scene, but do not necessarily originate in that location. By establishing the provenance of the sediment based on specific characteristic microfossils, the micropalaeontologist is able to assist in the investigation by potentially linking a vehicle and its user with a crime scene. This study examines the use of both foraminifera and calcareous nannoplankton in criminal investigations. It focuses on the importance of both microfossil groups during the police investigation of the Soham murder case in which these microfossils were used to place the suspect’s vehicle at the location where the bodies of the two victims were found. Clear recognition of both the foraminifera and the calcareous nannoplankton on the vehicle as being from a stratigraphically constrained unit of the Cretaceous Grey Chalk, and the establishment of its provenance, were a major element of the prosecution case. Other lithological criteria, including the mineralogy of the chalk and the field evidence regarding access routes and site topography, were also used to exclude alternative potential sources for the chalk on the vehicle.