Customary International Law as a Source of Individual Criminal Responsibility

Abstract In the Abd-Al-Rahman judgment of 1 November 2021, the Appeals Chamber of the International Criminal Court (ICC) was asked to rule on the compatibility of the ICC’s exercise of jurisdiction over the accused with the principle of nullum crimen sine lege. The question was motivated by the fact that the alleged crimes had neither been committed on a state party’s territory nor by a national of a state party. This article focuses on the answer provided by the Appeals Chamber and on the issues raised by its judicial reasoning. First, it discusses the legal sources to be applied in the context of criminal proceedings before the ICC with respect to situations not involving states parties to the Rome Statute. Second, it reflects on whether and to what extent customary international law may be referred to as the main source of individual criminal responsibility in such proceedings without infringing the principle of nullum crimen sine lege. In this respect, the article also analyses the accessibility and foreseeability test with specific reference to customary norms.