Linking Crimes

Chapter 4 examines how investigators and analysts determine whether separate crimes are connected and part of a larger pattern. Two main approaches are presented: comparative case linkage, which uses structured comparisons of time, location, modus operandi, and target selection, and formal case linkage, which applies systematic coding, variable weighting, and thresholds to assess similarity and difference across cases. The chapter contrasts police practice, which is focused on workable leads and investigative value, with research approaches that emphasize accuracy, error rates, and standardized protocols. Four reasoning methods are outlined: induction (building patterns from cases), deduction (matching crimes to known offenders), abduction (testing hypotheses through exploratory searches), and retroduction (identifying underlying conditions or mechanisms that explain observed patterns). Additional tools such as anomaly recognition, crime indicators, and crime script analysis expand linkage possibilities. Finally, the chapter discusses challenges to crime linkage, including limited or inconsistent data, resource constraints, interagency barriers, and the risks of bias. A practical exercise encourages the application of script analysis