Exclusion of evidence in times of mass surveillance. In search of a principled approach to exclusion of illegally obtained evidence in criminal cases in the European Union

The article discusses the rationales for excluding illegally obtained evidence in criminal cases starting from two recent judgments of the European Court of Justice on mass data collection. The two decisions concern the exclusion of evidence obtained as a result of the retention of metadata in breach of EU law. According to the ECJ, exclusion may be justified by on the basis of the principle of effectiveness and the consequent need to protect the suspects’ rights (protective principle). Based on its analysis of these recent cases, the article demonstrates how important the choice of a rationale for excluding evidence is. It discusses the different exclusionary principles that could be adopted and illustrates their practical implications. Finally, the article advances a proposal of a cascade system of principles for exclusion of evidence in the context of criminal proceedings in Europe.