Do International Criminal Court (ICC) indictments reduce atrocities? The ICC convicting only ten perpetrators since its founding in 2002 has generated skepticism of the court’s ability to prevent attacks against civilians. Drawing on the criminal violence literature, this article applies the concept of assurance to explain how the ICC reduces atrocities despite its limited capacity. As with criminal organizations facing domestic indictments, armed groups affiliated with ICC indictees often (mis)perceive that the indictments come with assurance: that is, inductee-affiliated groups believe that they can alleviate the costs imposed by indictments if they refrain from further attacks. I test the effect of ICC indictments on violence using the weighted regression method generalized synthetic control to mitigate empirical challenges posed by endogeneity and data unreliability. The results indicate that indictments lead to a substantial initial decline in attacks against civilians by armed groups affiliated with indictees, but the attacks return to pre-indictment levels when indictees face sustained punishment from the court. Descriptive cases of ICC indictments against alleged perpetrators in Uganda and Kenya are used to illustrate the role of assurance. These findings imply that the ICC might reduce violence by engaging in plea bargains and other negotiated settlements – tools commonly employed by domestic prosecutors fighting criminal organizations.