A fundamental principle of homicide investigation is to start by examining the partner of the decedent. Investigators in some countries are taught to evaluate the partner’s emotional affect when assessing whether the partner can be ruled out as a suspect or not. If emotional displays are “strange” or absent, investigators may be more likely to focus their attention on that individual as the suspect. But do strange or absent emotional reactions have any probative value for distinguishing homicide perpetrators from non-perpetrators? This chapter presents a framework for assessing the probative value of “strange” emotional reactions to homicides. Whether strange emotional reactions have any probative value depends on how common strange reactions are among homicide perpetrators and how common they are among non-perpetrators. We review the empirical literature that bears on these two frequencies. While there is a developed literature on emotional reactions to homicide from non-perpetrators, and such findings suggest a high degree of variety in responses, only a handful of studies have systemically examined the emotional reactions of homicide perpetrators. This lacuna makes it difficult to draw inferences from the emotional reactions of people about their guilt or innocence. Implications for homicide and other similar investigations are discussed.