Introduction: the issues of interaction of the investigator, as the central figure in the process of investigating crimes of extremism, continue to be the object of attention of scientists and practitioners. And this is not surprising, because the state of interaction of the investigator with the body of inquiry, the representatives of other services and departments, first of all, the law enforcement agencies directly depends on the speed of solving and the completeness of the investigation of each committed extremist crime, and this, in turn, affects the prestige of law enforcement agencies among the population and, as a result, the level of criminogenic situation. Despite the large number of recommendations available in the legal and specialized literature aimed at improving certain aspects of this type of activity of the person conducting the investigation, the dynamically developing criminal procedure legislation, as well as actively changing the operational-search and investigative practice, provide new food for analyzing the current state of interaction, in order to identify those newly emerging factors that negatively affect the organization and state of interaction of the main subjects of the investigation and which, ultimately, have a negative impact on the course and results of the investigation. In this regard, the authors aim to highlight some problematic issues that arise in the course of organizing and maintaining the proper level of interaction between the investigative body and other subjects of the investigation to ensure the prompt and comprehensive establishment of all the circumstances to be proved. Tasks: to describe the areas of interaction between the investigator and the body of inquiry during the investigation of crimes in cases of extremism; to give recommendations aimed at overcoming these problems. Methods: the methodological framework for the study is a set of methods of scientific knowledge, among which the main ones are the methods of information processing and logical analysis, synthesis, induction, deduction and generalization. Results: the authors’ point of view on the problems associated with the organization of interaction between the investigator and employees of other services and departments of the law enforcement agencies in order to uncover and investigate crimes of extremism, as well as the proposed ways to solve them, based on the analysis of modern operational and investigative practice, trends in the development of the current criminal procedure legislation make it possible to use them in the practical activities of the authorized law enforcement officials in their practical activities aimed at solving and investigating crimes. Conclusions: as a result of the study, the existing problems determined by the changes in the criminal procedure legislation and operational and investigative practice are identified, and the ways to overcome them are proposed in order to inform students in the field of training “Jurisprudence”, teachers of law schools, as well as practitioners in order to better understand the specifics of the investigation of crimes of this category.