A few years before the expected convening of the First Review Conference on the Statute of the International Criminal Court, the Special Working Group for the Crime of Aggression has made very significant progress in preparing the ground for enabling the Court to exercise its jurisdiction over what the Nuremberg Tribunal famously called the ‘supreme international crime’. The complex structure of this absolute leadership crime has been fully explored, including its implications for the interplay between the definition of the crime and the general principles of international criminal law. At the same time, the crucial analytical distinctions between state and individual conduct as well as between the substantive elements of the crime and the possible procedural role of the UN Security Council appear to be generally accepted. In the light of the momentum achieved on the diplomatic level, the First Review Conference presents a distinct and historic window of opportunity to the world's political leadership to complete the Rome Statute and thereby prevent its prominent lacuna from becoming permanent and thus turning into a legitimacy gap. The final phase of the negotiations should be guided by two principles. First, the substantive definition of the state act of aggression should stay within the legitimate limits of international criminal justice by not exceeding undisputed general customary international law. Second, a possible procedural role for the Security Council must not have the practical effect of placing the permanent members of the Security Council beyond the reach of the law.

This contribution is dedicated to Professor John Dugard. It discusses the most difficult issue to be resolved in the negotiations on the crime of aggression: the role of the Security Council in the exercise of jurisdiction over this crime by the International Criminal Court. The International Law Commission suggested a solution in the 1990s, but failing the required support and in the absence of subsequent agreement the 1998 Rome Conference could only prospectively give the Court jurisdiction over the crime of aggression. The post-Rome negotiations are characterized by, on the one hand, support from the five permanent members of the Security Council for the thesis that it should be exclusively for the Security Council to determine whether or not an act of aggression has been committed (as a precondition for the exercise of jurisdiction by the ICC) and, on the other hand, a rejection of this thesis combined with a search for alternatives by many other states. According to the analysis below, in relation to cases involving the crime of aggression the preferred way for the ICC to proceed is to exercise jurisdiction over this crime after a determination of state aggression has been made by the Security Council. Nevertheless, the view according to which such a determination could exclusively be made by the Council is rejected, on the basis of the rules of the Charter, the practice of the Security Council and the General Assembly, and decisions of the International Court of Justice. Finally, an alternative arrangement is suggested for the cases in which the Security Council is prevented from acting because of the use of the veto or because of lack of support from its members.