ENIn any state where the rule of law is applied, criminal justice serves to guarantee the efficiency and legitimacy of liability and all legally sanctioned coercive measures. Its purpose is also to eliminate, insofar as is possible, any arbitrariness and dishonesty arising in the course of criminal prosecution. Thus, the rules underpinning criminal law and procedure, formulated precisely, harmonized, and based on the principles of law, are the theoretical basis for the attainment of those objectives. In reality, however, the activity of the legislator in drafting new laws and slowed progress in eliminating outdated and unjustified norms creates a situation where the wording of legal codes gradually loses their systematic and consistent character. In recent years, the phenomenon of over-criminalization and statutory ambiguity has attracted an enormous amount of research interest in criminal science. A number of legal concepts and principles are used to discipline the legislature, and thereby allow the courts to apply the law prudently and with great caution, within the limits of their constitutional powers, and in accordance with local legal traditions. This paper presents those legal principles followed by the Lithuanian courts to ensure the proportionate application of substantive criminal law and special investigative techniques, inter alia secret surveillance, thereby osetting the impact of poorly drafted laws on human rights. [From the publication]