This study analyzes the methods used by international criminal tribunals when determining customary international criminal law and to consider the compatibility of these approaches with the nullum crimen sine lege principle.
Introduction.- State responsibility and the criminal liability of the individual.- Nullum crimen sine lege.- The formation of customary international law and its methodological challenges.- The role of judges when determining customary international law.- Methodological approaches to customary international law by international criminal tribunals.- Relevant material for proving the existence of customary international criminal law.- Conclusion.