Judicial decisions of the International Criminal Court and other international criminal tribunals now serve as instances of practice and statements of opinio juris for the formation of customary international criminal law and customary international human rights law related to criminal law and procedure. In these areas of law and others, they are no longer “subsidiary” sources as that word is used in the International Court of Justice Statute, Art. 38. In the same fields of customary international law, other binding acts of international organizations, such as the UN Security Council, are also used as practice, and the statements of these organizations are used as opinio juris.
Where judicial and quasi-judicial decisions of international organizations are acts of treaty interpretation and application, these acts are instances of subsequent practice. In some cases, judicial decisions play a role similar to the subsequent acts of states parties to the treaties in the Vienna Convention of the Law of Treaties. Under the ICC Statute, when the Court is interpreting a matter within its judicial competence, its decision is authoritative.
Individuals, particularly those accused of crime, can make direct claims of right under international law to these courts and tribunals. These claims may concern jurisdiction, the substantive law of crimes and defenses, international human rights in criminal procedure and criminal law, or other issues that arise in the course of prosecutions.
The expanding role of international organizations, including the international judiciary, in the process of making international law is being led by the ICC and other international criminal tribunals. It is already spreading to other areas of the law, such as international trade law. This growth is likely to continue.
Individuals have gained the right to make claims directly under international law in certain non-criminal international fora. As in criminal law, the right depends on the agreement of states or international organizations to establish these tribunals. While the growth of this right is uncertain, it is hard to imagine that it will be cut back.
Kenneth S. Gallant, International Criminal Courts and the Making of Public International Law: New Roles for International Organizations and Individuals, 43 J. Marshall L. Rev. 603 (2010).