The analysis of the principle of the complementarity formula set out in the Rome Statute is at the heart of this dissertation. The research aims to critically reflect on the complementarity regime under the Rome Statute in relation to international crimes committed in the DRC since the incorporation of the Rome Statute into the Congolese legal system. This research argues that the implementation of the principle of complementarity poses difficulties of application, implementation, and interpretation and thus remains a less effective means of putting an end to international crimes. The findings of this research indicate an urgent need for the principle of complementarity being rethought by clarifying its content and scope. Victims of international crimes cannot to date rely on its implementation to obtain justice. This research adopts an essentially conceptual approach; moreover, the methodological approach adopted is that of qualitative research. This research calls for the principle of complementarity being rethought by clarifying its content and scope.

The principle of complementarity is a tool used to punish the commission of core international crimes. A concerted approach is required to combat war crimes, genocide, crimes against humanity and aggression. The Prosecutor of the International Criminal Court needs to fully appreciate the express and implied discretionary powers of states to ensure all possible accountability mechanisms are explored. Failure by the Prosecutor to do so results in missed opportunities to capitalise on various options related to the proper application of complementarity. Therefore, there is a need for consultations to establish that the International Criminal Court and prosecutions can no longer exist without competing alternatives preferred by states. The current misunderstandings on the application of complementarity are rooted in unresolved state and prosecutorial discretions. The endangering of state discretion threatens the integrity and credibility of the International Criminal Court. The unaddressed question of state discretion is also at the centre of disputes between the African Union and the International Criminal Court. Grey areas in the application of complementarity are clearly visible through the inconsistency and diversity of the International Criminal Court decisions and frequent prosecutorial policy proclamations. As a result, prosecutorial discretion needs to be checked. Prosecutorial discretion is checked at the United Nations, International Criminal Court and state levels. The checks at regional level and by non-prosecutorial options need to be explored. The call is for the International Criminal Court not to neglect the legal-political environment which the Court operates in. The environment is essential in demarcating the exercise of discretions. The Kenyatta case is illustrative of the need to invent an interpretation that reflects the evolving theory to practice reality. The development or amendment of a prosecutorial policy is desirable to give guidance on the value, circumstances and priority accorded to justice. The policy should be comprehensive enough to accommodate mechanisms which advocate for strengthened state discretion. For instance, African Union instruments and treaties reveal that the respect of state discretion is one of the core principles of the African Union system. / Public, Constitutional, and International Law / LL.D.