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The Rome Statute as Evidence of Customary International Law

In 2005, the International Criminal Court (ICC) in The Hague started an investigation on alleged crimes in Darfur, Sudan. However, Sudan is a non-party state to the Rome Statute wich formed the basis for the establishment of the ICC. PhD candidate Yudan Tan studied the status of the Rome Statute and she will defend her thesis on 9 April.

Treaty and customary international law are the two main sources of international law and their relationship remains a controversial topic, Tan explains. ‘Generally speaking, the two sources have different binding force. A written treaty is binding upon States Parties to it, while an unwritten customary rule is binding on all states.’

Yudan Tan

This dissertation, therefore, aims to examine whether and to what extent a rule of the Rome Statute was or is declaratory of a customary rule on the same subject matter. ‘Treaty and customary law may co-exist in contexts where a customary rule is identical to a treaty text, and where there were different rights and obligations under customary rules and treaty provisions with respect to the same subject matter. It is possible that only a treaty rule existed on the subject matter under international law at the time when the treaty was adopted, but the practice of this treaty rule progressively develops into a customary rule later. Thus, a treaty rule may reflect a parallel customary rule, depart from an exisiting customary rule, or develop into a new customary rule.’

The ICC has the power to exercise jurisdiction with respect to the most serious international crimes committed on the territory of a State Party or committed by a national of a State Party. ‘However, in certain circumstances, the ICC may also exercise jurisdiction over a crime committed by nationals of a non-party State on the territory of a non-party State. A good example is the situation in Darfur, referred to the ICC by the UN Security Council. As a result of the Security Council’s referral, the ICC has exercised jurisdiction over alleged crimes committed by Al Bashir in the territory of Sudan. It should be noted that Sudan is a non-party State to the Statute and the accused are also nationals of a non-party State.’

Principle of legality

The alleged crimes were committed prior to the Security Council’s referral to the ICC. ‘On the other hand, the principle of legality prohibits retroactive prosecution of crimes. A question arising here is how the ICC can exercise jurisdiction over this situation without violating the principle of legality. First, it seems that the Rome Statue is not automatically applicable in prosecuting these alleged crimes. Second, it is suggested in the absence of other relevant national criminal prohibitions at the time of the alleged conduct, customary law would be presumed a legitimate and substantive basis to establish individual criminal responsibility. Lastly, since the ICC ‘shall’, in the first instance, apply the Statute rather than customary law, the ICC in this context may have to establish whether offences in the Statute are reflections of customary law at the material time. Therefore, it is necessary to study the status of the Rome Statute as evidence of customary international law.’ The dissertation concludes that provisions of the Rome Statute were partly declaratory of custom when adopted in 1998, and that they are also partly declaratory of custom at the present time.

This study of the nature of the Rome Statute as evidence of custom has substantial practical significance, according to Tan. A number of studies have examined and commented on rules of the Rome Statute and the practice of the ICC, but apart from a few writings on a rule of the Statute as a reflection of or departure from a pre-existing customary rule, there has been little research dealing with rules of the Statute as evidence of parallel customary rules and as evidence of the progressive development of custom. ‘This research is relevant in situations where non-party States to the Statute become involved in proceedings before the ICC. In addition, this dissertation hopes to provide practising international criminal lawyers with novel arguments and materials by which to assess a case in favour of or against the existence of a customary rule or the applicability of the Rome Statute to specific issues.’

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