Summary of master's thesis (criminal procedure) The master’s thesis concerns the public prosecutor’s role in a criminal investigation. The author presents the main powers and duties of prosecutor and calls into question if he’s still the dominus litis of pre-trial proceedings. Analyzing the above mentioned point, it was necessary to raise issue of prosecutor’s role in both form of criminal investigation, indicate proceedings reserved to prosecutor and his relationship with another authorities, especially Police. The prosecutor’s supervision of proceedings conducted by another authorities was mentioned as well. The author has paid special attention to the relationship between prosecutor and court carrying out judicial acts, thereby referring to the institution of investigation magistrate. Consequently, the possibility of extension of court’s competences was elaborated (judicial decision of search, appeal against charges or judicial control under article 302 of Code of Criminal Procedure). It is to be noted that the subject of consideration was also prosecutor’s powers in relation to closure of pre-trial proceeding, that is resumption under article 327 § 1 of Code of Criminal Procedure and revision of proceedings under article 327 § 2 of Code of Criminal Procedure. The highlighted topic was elaborated in comparative approach, because the author has presented the model solutions of Spanish and English system. Therefore, it was raised the institution of judicial investigation and relationship between the magistrate (el juez de instrucción) and the prosecutor (el fiscal), English legal regulations and the Crown Prosecution Service as well.