The Admissibility of Unlawfully Obtained Evidence before International Courts and Tribunals

70 years ago, the International Court of Justice decided its first and potentially most important case involving unlawfully obtained evidence. Despite clearly rejecting ‘discovery by intervention’, the judgment left many guessing as to the consequences for evidence obtained through such violations. As parties to international disputes have certainly not become less inclined to obtain evidence by unlawful means, the question arises: Was this old confusion ever unraveled? This article discusses whether today, there are international rules or principles governing the admissibility of unlawfully acquired evidence and applies a two-fold approach. First, it examines traditional sources of international law, including international jurisprudence, and second, it scrutinizes the frequently drawn analogy to national jurisdictions by surveying their treatment of illegally obtained evidence. Although a generally binding “inadmissibility rule” does not yet exist, practice demonstrates a tendency to consider such evidence in light of general principles of law. This article proposes handling unlawfully acquired evidence by applying a defined, yet flexible balancing test using criteria commonly applied in international and national practice.