The experience of violence has powerful consequences in the transformation of history. The 1923 Great Kanto Earthquake marked a moment of unprecedented material destruction and cultural rupture in the Japanese empire. The disaster soon became subject to human interpretation and political manipulation, for the trauma of the earth tremors and subsequent fire produced not only physical chaos, but also rumours and violence against the colonized in the metropolitan area. Such violence manifested itself in the massacre of Koreans immediately following the earthquake-triggered by rumours of arson, murder, and riots by Koreans in the Tokyo-Yokohama area. Despite the shock of rumours and mayhem, the lack of critical evidence and the contradictions in testimony have rendered the incident an historical enigma in modern Japanese and Korean history. Interestingly, precisely because of this unsettled nature of the violence - which thus defies any singular narrative that satisfactorily explains the incident empirically - the event illuminates the development of subjective narratives on collective violence. In an attempt to explore the relationships that weave together disaster, rumours, massacre, and narrative-making in the culture of empire, this paper explores collective violence through the lens of rumours and vigilante trial discourse in the context of imperial Japan.