The contribution of customary international law to the development of international crimes: the role of international courts and tribunals

The development of international crimes rightly touches the statement, ‘desperate ills need desperate medicines’, made by Mr C.B. Burdekin, a representative from New Zealand, during the thirty-sixth meeting of the United Nations War Crimes Commission on 17 October 1944. The thesis is intrigued by the fact that the development of international crimes suffers from an identity crisis. Finding sources of crimes within the rules of customary international law always appears with multiple complexities.
The thesis observes the evolution of international crimes under customary international law starting from World War I. It aims to analyse the evidence that were instrumental to the making, developing, identifying the elements of international crimes. The thesis intensively looks into the contribution of customary international law in the development process of international crimes. It analyses whether the sources referred by the international courts and tribunals as evidence of law satisfy the two-element approach of customary international law or have been used merely as a tool to reconcile with the principle of legality. The primary aim of the thesis is twofold: first, it examines the sources of international crimes identified by the international courts and tribunals, and second, it analyses whether there is any separate ascertainment of the sources justifying the presence of State practice and opinio juris.
Like other scholars, the thesis notices inconsistent methodologies of the custom identification process. Methodologies are diverse and highly influenced by several external variables. However, unlike others, the thesis does not entirely emphasise value-driven opinio juris; instead, it finds the existence of opinio juris appears from international legal norms, principles and instruments and suggests an international practice-based opinio juris.