This study examines the interaction between the victim and offender during intrafamilial homicide. It is hypothesised that in order to understand the fatal consequences of the interaction, a psychological model must take into account both the role of the victim, as either a significant person or non-significant object, and the function of the aggression, as either instrumental or expressive. The combination of these two proposed facets gives rise to four hypothesised styles of intrafamilial homicide. This hypothesis was tested by analysing 191 intrafamilial homicide cases from the Chicago HITS database. Fifty two crime-scene actions were analysed using Smallest Space Analysis which revealed four distinct thematic clusters of variables. These themes corresponded to the hypothesised facets of victim role and function of aggression. Two related to expressive acts, (a) those murders where the offender kills multiple members of his family and subsequently takes his own life, and (b) cases where the victim is not treated as a significant person in the interaction but is simply used as a target for the offender's rage. The other two relate to instrumental acts, (c) those murders that are a culmination of years of abuse in which the offender sees the killing as the only means of escape, and (d) homicides where the victim is seen as an obstacle to the offender achieving a goal and is removed. A further test of the validity of these four themes in describing distinct forms of interaction within intrafamilial homicide was to examine the proportion of cases which could be classified according to the framework. The hypothesis that each relationship would map onto just one of the interactional styles was tested by χ2 which confirmed that such exclusive relationships existed at the p <.001 level of significance. This has theoretical as well as practical implications in that in using this method of classification it may be possible to infer which family member is responsible for killing their relative.