The Subsidiary Prosecutor as a traditional institution of the Croatian legal system, has undergone major changes by the entry into force of CPC/08. Such changes are further strengthened by the conclusion number 6. of the Supreme Court Criminal Division and the Presidents of all the County Courts Criminal Division which were adopted on October 1, 2018. In order to better understand the subsidiary prosecutor and its current organization as a mechanism for controlling the decision not to prosecute, the first part of the paper deals with the analysis of the European Convention for the Protection of Human Rights and Fundamental Freedoms. Particular attention has been paid to the analysis of the legal standard of effective investigation that has been developed through the case law of the European Court of Human Rights. Elements of the legal standard of effective investigation, such as victim involvement and the right to effectively control the decision not to prosecute, are also analyzed in greater detail. Directive 2012/29/EU establishing minimum standards for the rights, support and protection of victims of crime as a legal means of harmonizing criminal law in EU Member States more specifically regulates this area of victim rights and is a significant step forward in this regard. Accordingly, the second chapter of the paper deals with the Directive itself and. In the context of the analysis of the Directive, particular attention was paid to the right to inform the victim and to control the decision not to prosecute. Following the establishment of European legal standards, the third part of the paper deals with the comparative analysis of mechanisms of the control of the decision not to prosecute in Austrian, German and Italian legislation, with a critical review of individual solutions from these systems. The last section of the paper analyzes the mechanisms for controlling the decision not to prosecute and their current regulation in the legal system of the Republic of Croatia. Particular attention was paid to the subsidiary prosecutor, its current arrangements and the real and financial burdens imposed on the injured party as a subsidiary prosecutor. The conclusion proposes to change the current regulation of the subsidiary prosecutor with the aim of greater efficiency, alignment with European legal standards and with the legal nature of the subsidiary prosecutor.