The deterrence of international crimes in a pluralist legal order

International crimes are extraordinary crimes that threaten the values of the international community. They may be prosecuted by multiple international and national institutions, producing ‘jurisdictional pluralism’: the existence of concurrent claims to jurisdiction. The conflict in the former Yugoslavia illustrates this phenomenon, involving numerous actors operating under different legal frameworks. Against this backdrop, the dissertation examines the legal and behavioural implications of the pluralist architecture of international criminal justice. The dissertation proceeds from the premise, grounded in rational choice theory, that deterrence depends on the combined operation of three elements of punishment: probability, celerity, and severity. Although deterrence does not require certainty, it assumes that individuals can form reasonably accurate expectations about the consequences of their conduct. Jurisdictional pluralism complicates this assumption by exposing perpetrators to divergent legal frameworks. The comparative legal analysis and the empirical analysis of sentencing data reveal that offenders operating within a pluralist system indeed face an unpredictable punitive landscape, making it difficult to estimate the probability, timing, and severity of punishment. The subsequent experimental analysis, although not finding support for the central hypotheses – that ambiguity in sanction severity may enhance deterrence due to ambiguity aversion, or alternatively, undermine deterrence by eroding perceptions of fairness – highlights that punishment, regardless of its (un)certainty, significantly deters harmful behaviour. Overall, the dissertation argues that ensuring international crimes are both punishable in law and punished in practice is essential for deterrence. Jurisdictional pluralism offers a key advantage by increasing the likelihood that perpetrators will face legal consequences. At the same time, it raises concerns about legal certainty and predictability. While inconsistencies do not necessarily generate perceptions of unfairness or undermine deterrence, such issues may be particularly significant in transitional justice contexts. The benefits of pluralism must therefore be balanced against its potential costs for coherence and legal certainty.