Numerous publications are appreciated for being a gap filler. Naturally, in certain sense, each book, paper, scientific work, etc. can be considered in this way but in most cases this formulation in reviews means just a polite phrase towards the author. The newest book of János Sallai can be regarded as a veritable gap filler. Those, who are a little bit familiar with the area of law enforcement science, know how great the gap was on this field of law enforcement history. A part of its reason can be read in the preface of the book: „ The research of the history of the Hungarian law enforcement and police did not happen in the socialist era because of the continuous denial of the past.” Only after the system change was opened the possibility to search in this topic, but in spite of numerous articles and books published, the education of law enforcement history did not become part of the training program in the secondary and the higher education of law enforcement in the long run.