Mass atrocity prosecutions are credited with advancing a host of praiseworthy objectives. They are believed to impose much-needed retribution, deter future atrocities, and affirm the rule of law in previously lawless societies. However, mass atrocity prosecutions will accomplish none of these laudable ends unless they are able to find accurate facts. Convicting the appropriate individuals of the appropriate crimes is a necessary and foundational condition for the success of mass atrocity prosecutions. But it is a condition that is frequently difficult to meet, as mass atrocity prosecutions are often bedeviled by pervasive and invidious obstacles to accurate fact-finding. This Article deconstructs those obstacles. Isolating fact-finding challenges and ascertaining their impact is no mean feat because mass atrocity prosecutions are a heterogeneous combination of a variety of different kinds of crimes and different kinds of proceedings. Mass atrocity prosecutions take place in international courts, domestic courts, and hybrid international/domestic courts. Mass atrocity prosecutions encompass international crimes and domestic crimes, and they encompass a wide range of horrific acts perpetrated by a wide range of individuals, acting in a wide range of contexts. Previous scholarship has identified international criminal law as a discipline intensely marked by pluralism; this Article contends that that same pluralism characterizes the fact-finding challenges that confront international criminal prosecutions. Moreover, this Article advances the debate by isolating three particularly significant factors likely to create factual uncertainty at trial. Taken together, this examination produces a startling revelation: that the “gold standard” of mass atrocity prosecution— international criminal tribunal prosecutions of international crimes—is at greatest risk for inaccurate fact-finding at trial.