I study the history of criminal detection as a mode of knowledge production in British India that emerged at the interface of police work, criminal trial procedure, forensic scientific research, and popular fictional and journalistic writings in the 19th and early 20th century, with a sustained focus on British Bengal. Against the grain of both common-sense and academic understanding, that conflate criminal detection with either police work or genre-fiction, and associate epistemology somewhat exclusively with discourses of law and science, I argue that the career of criminal detection in British Bengal allows us to envision a history of epistemology that is not simply a history of abstract ideas, and elite-academic pursuit, but as a concrete institutional and political history of material and collaborative practices that cut across a wide range of social, professional, disciplinary, and imperial divides. In my work I show that the lens of criminal detection allows us to see how key ideas about evidence, certainty and proof in the production of knowledge, that form the very standards by which we continue to know the world, evaluate information and judge human actions, were worked out in response to the everyday challenges of administering crime in the colony; that far from being just an 'ideology' of colonial rule, methodological debates in a set of 19th and early 20th c. field and laboratory based sciences permeated the colonial 'rule of law' in concrete ways. It also underscores the active role that a colonized population played in receiving, contesting and shaping these legal and scientific ideas. My work brings together legal history and history of science, medicine and technology to explore the imbrications of colonial state practices and a subject populations' negotiation with colonial rule, through an analysis of the epistemological challenges that producing knowledge about crime presented in British India.