This book is the result of a very long, sometimes overwhelming, but eventually very fulfilling and satisfactory period of research. Therefore, the list of institutions and people that I am indebted to is extremely long. The study was carried out with the financial support of the Polish National Science Center (Narodowe Centrum Nauki) that granted me funds that allowed my ideas and dreams to come true (research project no. 2014/ 15/ D/ HS5/ 00658 entitled “The Role of the Prosecutor in Criminal Investigation – comparative perspective”). Three universities have welcomed me generously and allowed me to conduct the research on their premises and provided me with hospitality and support: The University of Bologna, the University of Cologne, and the University of Connecticut.