Expressiveness and instrumentality in homicide: Hybrid crime scenes and the links among situations, psychological processes, and actions

The expressive/instrumental classification of homicide (Salfati, 2000) can categorize the majority of crime scenes in data sets. However, hybrid scenes cannot be allocated into a subtype because they do not display a dominant behavioral style. Addressing the problem of hybrids involved assessing the individual behaviors that comprise the classification system. Study one confirmed the model within a U.S. data set comprised of 210 single offender homicide cases and classified 69% of crime scenes. The behaviors that comprised expressive, instrumental, and hybrid scenes were examined and behavioral similarities among instrumental and hybrid crime scenes were identified. Study two developed the theory behind the classification in an effort to explain why some crime scenes involved both expressive and instrumental behaviors. Crime scene actions included within the model were refined to reflect lower-order goals in accordance with the theoretical advancement. The model refinement resulted in 84% of crime scenes being classified in study two. Underlying dimensions within lower-order goals were examined with multiple correspondence analysis and interpreted with respect to psychological processes important to information processing. Crime scenes were grouped together based on their similarity in lower-order goal actions with cluster analysis and interpreted with respect to situations and psychological processes. The results suggested important similarities and differences in the actions, which characterized expressive, instrumental, and hybrid crime scenes. Implications for theory, research, and practice were further discussed.