His major research interests are in international law and criminal law. In addition to a number of articles and book chapters he is the author of Prosecuting International Crimes: Selectivity and the International Criminal Law Regime (Cambridge: CUP, 2005 (pb 2011)), which discussed the interrelationship of the personal and material jurisdiction of international criminal tribunals. He also has written on war crimes trials in Asia, most notably as the co-author (with Neil Boister) of The Tokyo International Military Tribunal: A Reappraisal (Oxford: OUP, 2008), which has contributed to the renaissance of scholarship on this Tribunal. He is also co-author (with Hakan Friman, Darryl Robinson and Elizabeth Wilmshurst) of the widely used textbook An Introduction to International Criminal Law and Procedure (Cambridge: CUP, 3rd ed,. 2014). He is co-editor of the Journal of Conflict and Security Law and a member of the editorial board of the Journal of International Criminal Justice and is currently working on a number of projects, including a book on the application of international humanitarian law by international criminal tribunals, and other pieces on the sources and history of international law.