This paper considers the development and interaction between two new sites of scientific practice in the interwar period – the crime scene as a space of disciplined investigation, and the crime laboratory as the site for the deployment of new techniques and technologies of investigation. To be of use to the crime lab, crime scene officers needed to be instructed both about the new analytical horizon opened up by these institutions, but about how they needed to conduct themselves in and treat the crime scene and the traces they harvested from it in a manner that was compatible with the needs of the labs.