The Biological Weapons Amendment to the ICC Statute and National Provisions: Mutually Reinforcing Evidence for Customary Criminalization?

This article analyzes the 2017 amendment to the Rome Statute of the International Criminal Court (ICC) that explicitly criminalizes the use of biological weapons in both international and non-international armed conflicts as war crimes. It examines how this amendment has influenced national legislation among the 18 states that have ratified it, noting that most had already prohibited biological weapons use under various legal frameworks, while some adopted or amended laws in direct response to the ICC amendment. The study highlights that although the prohibition of biological weapons is widely recognized as customary international law, the criminalization of their use as individual war crimes required further state practice and opinio juris, which the amendment and subsequent national legislation help to reinforce. The article also discusses the absence of a legal obligation for states to implement ICC provisions domestically but emphasizes the role of complementarity in motivating such implementation. Overall, the amendment’s adoption and national incorporation contribute to strengthening the customary international law status of criminalizing biological weapons use in armed conflict.