Chapter seven addresses the question of why some Rwandans killed and others not. Drawing on original data, it provides new estimates of the number of individuals killed and the number of individuals who participated in the violence. It finds that an astonishing one in five Hutu men committed an act of violence during the genocide. However, this still means that four in five did not. Drawing on survey data of 294 Rwandans, the chapter then systematically compares perpetrators against non-perpetrators. Consistent with the consensus on 'ordinary men', it finds few statistically significance differences between them. However, using other evidence, the chapter shows that important dispositional differences nonetheless existed that the perpetrator sample, drawn exclusively from within the prison system, did not capture. It distinguishes between extremists, opportunists, conformists, and pacifists. Perpetrator heterogeneity existed. Differential selection into the violence was not solely dispositional, however. The chapter shows that situational and relational forces also mattered. It maps the household locations of 3,246 residents of a single Rwandan community and finds that where you lived in part determined whether you would be drawn into the violence. Spatial proximity increased the opportunity for ‘social influence’ - the induction of individuals, through coercion or persuasion, into the violence. The chapter also maps the social networks of 130 Rwandans. It finds that who you knew also mattered.