Genocide on Trial investigates the everyday of witnessing at Rwanda’s Gacaca courts and contrasts its findings with the process of witnessing at the International Criminal Tribunal for Rwanda (ICTR). The Rwandan Gacaca courts have attracted considerable academic attention ever since the courts began their work in 2002, yet we still know little about the role witnesses played in the collection of evidence and in the trials themselves. In this paper, I ask: who were the witnesses at Gacaca? What role did survivors play? How were their testimonies used in the decision-making process of the Gacaca judges? In answering these questions, I aim to establish a typology of witnesses at Rwanda’s Gacaca courts and explore how these different forms of evidence gathering and witness testimony – at the ICTR and Gacaca – recount and reshape our (legal) understanding of the atrocities committed. In doing so, I draw upon numerous interviews with former Gacaca judges conducted throughout Rwanda between 2017 and 2018. This research is generously supported by the Leverhulme Trust Fund.