The chapter explains the principles of inter-state cooperation in criminal matters in connection with domestic proceedings. It sets out the international legal framework governing criminal law cooperation among states, including multilateral and bilateral agreements of general application and treaties specifically concerning international crimes, most notably the 2023 Ljubljana–The Hague Convention on International Cooperation in the Investigation and Prosecution of the Crime of Genocide, Crimes Against Humanity and War Crimes. The chapter sets out the differences between the traditional forms of assistance in criminal matters, which are associated with a higher degree of formality and subject to broader grounds for refusal and, on the other hand, the more advanced forms of cooperation (exemplified by mutual recognition in the European Union context) prioritizing effective enforcement while recognizing limited grounds to refuse requests. The chapter reviews the prerogatives of the requested states to refuse under these models with reference to double criminality, specialty, statutory limitations, ne bis in idem, and human rights concerns. It then takes a closer look at the traditional forms of cooperation and the issues which arise in that context, focusing on extradition, other mutual legal assistance, transfer of criminal proceedings, and enforcement of foreign penalties.

With the principle of mutual recognition, the EU facilitates effective and efficient law enforcement cooperation among its Member States. Foreign judicial decisions are treated like domestic decisions, while differences in the national criminal justice systems are maintained. Prolonged examinations are no longer necessary and “safe havens” for criminals are closed. The basis of this cooperation, however, is mutual trust in the rule of law. The author uses, inter alia, the current example of Encrochat to show concrete possibilities for application. There, the French criminal authorities achieved a considerable cross-border investigative success by decrypting crypto-mobile devices of that company, which were frequently used by criminals. Through the recognition and execution of European Investigation Orders in France, those findings could also be used in other Member States and considerable prosecution successes achieved. However, the scope and variety of such measures can lead to problems: Only corresponding measures can be recognised. Violations of the Charter of Fundamental Rights EU must not be enforced. Inhumane treatment of detainees may prevent the enforcement of a European Arrest Warrant in individual cases. The loss of trust in the rule of law in some Member States, the EUs reaction to this danger and the control function of CJEU decisions are currently determining legal policy.

Previous chapters in this book have focused on domestic (or municipal) law within Hong Kong. This chapter examines the interface between Hong Kong law and international law and Chinese law (PRC law). It looks at the distinct international legal personality that Hong Kong possesses, Hong Kong’s engagement with international entities and the application of international law in Hong Kong. Previous chapters have discussed certain aspects of the interface between Hong Kong and the PRC legal system, and this chapter builds on this by focusing on mutual legal assistance between the two legal systems, access to the Mainland market for legal services from Hong Kong and cross-border crime.