Mutual Legal Assistance and Double Criminality

Abstract The Ljubljana–The Hague Convention on International Cooperation in the Investigation and Prosecution of the Crime of Genocide, Crimes against Humanity, War Crimes and Other International Crimes, adopted in May 2023, was accepted as more than a ‘pure’ mutual legal assistance treaty (MLAT), as, in addition to regulating issues of mutual legal assistance, it also addresses substantive international criminal law issues. In this article, it is argued that due to this less flexible approach, the Convention may not be as widely accepted as it was intended to be and therefore might fail to achieve its goal to prevent impunity. This article presupposes that a pure MLAT — which concentrates on collaboration between states on procedural aspects of criminal investigations and preparations for prosecution — may be attractive to more states. This article focuses on extradition and discusses how to regulate extradition if the requirement that member states adopt unitary definitions of international core crimes in their domestic laws were omitted from the treaty. It suggests dual criminality and a flexible interpretation of this principle as a basis for extradition of alleged perpetrators of core crimes between states that define the prohibitions on international core crimes differently. This article also addresses ‘the special use’ of dual criminality, which requires a match of jurisdictional bases between the states involved in the process of extradition, and questions whether or not it should serve as a bar to extradition. In this context, this article addresses universal jurisdiction (UJ) and makes proposals to provide states parties with the option to limit extradition requested on the grounds of UJ according to parameters such as complementarity and the involvement of the prosecuting state’s high legal authorities in the prosecution or investigation of the alleged offence.