Exploring the Ne Bis in Idem principle: Material scope and application in EU law

This article examines and analyses the application of the ne bis in idem principle based on a final verdict of acquittal or conviction by a competent court where the cases have already been concluded by a final decision. It examines the principle concerning Article 4 of Protocol No. 7 of the European Convention on Human Rights (Article 4P7 ECHR), Article 50 of the Charter of Fundamental Rights of the European Union and its implication under Articles 54 to 58 of the Convention Implementing the Schengen Agreement (CISA). By reviewing previous literature, case law and fact sheets of the Court of Justice on the Ne bis in idem principle, the paper analyses the material scope of application of the principle and highlights the multifaceted significance of the Ne Bis in idem principle in criminal proceedings and the harmonisation of legal practices within the European Union. It reaffirms the principle's foundational importance in fostering fairness, legal certainty, and the protection of fundamental rights across a wide array of legal contexts. It elaborates and provides an interpretative analysis of the principle on the associated jurisprudence of the Court of Justice of the European Union (CJEU) and the European Court of Human Rights (ECtHR). The paper also shows that the ne bis in idem principle serves as a common ground for judicial cooperation in criminal matters and mutual recognition of the Council Framework Decision 2002/584/JHA concerning the European Arrest Warrant (‘EAW FD’) and Directive 2014/41/EU regarding the European Investigation Order in criminal matters.