Par in Parem Imperium Non Habet: Complementarity and the Crime of Aggression

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The principle of complementarity undergirds the International Criminal Court’s admissibility regime. And yet, in the negotiations leading up to the 2010 Review Conference in Kampala, Uganda, delegates did not fully focus on the potential for the addition of the crime of aggression to destabilize the Court’s complementarity regime. The only guidance from the ASP came in the form of two interpretive Understandings that express a subtle preference that States Parties not incorporate the crime into their domestic codes. If States Parties heed this call - which they should - the Court will inevitably be faced with situations in which there is incomplete concurrence between the prosecuting state’s domestic law and the ICC Statute given that few states have codified the crime of aggression. Under prevailing interpretations of the principle of complementarity, however, a case would be admissible before the Court if a domestic court were prosecuting atrocity crimes, but not the crime of aggression. This paper argues that the Prosecutor should announce in advance of the amendments’ activation the intention to stay his or her hand in the event that genuine domestic prosecutions are going forward on the basis of charges of genocide, crimes against humanity, or war crimes, even if potential domestic aggression charges are not available, are legally barred, or are not forthcoming. The only exception to this general approach should be in cases in which the crime of aggression is the primary or central charge to arise out of a particular situation, such that atrocity crimes are non-existent or largely peripheral. This paper thus advocates that the ICC be allowed to exercise a de facto primacy over the crime of aggression vis-a-vis domestic courts, which will retain the ability to take the lead on prosecuting the atrocity crimes. Such a division of labor between the ICC and domestic courts will obviate a number of concerns associated with domestic prosecutions of the crime of aggression, encourage domestic prosecutions in keeping with the ideal of positive complementarity, reinforce the recognized duty of states to prosecute international crimes, and avoid over-burdening the ICC with cases that could otherwise proceed effectively in a domestic court. It will also ensure that to the extent that the crime of aggression is ever prosecuted, it is done in an international, rather than domestic, forum pursuant to a consensus definition of the crime and a negotiated jurisdictional regime.