The article substantiates that achieving the standard of a fair trial is impossible without the systematic involvement of specialists whose activities are aimed at increasing the efficiency of detecting, collecting, and properly recording traces of criminally unlawful activity, conducting special studies, as well as forming evidentiary information on their basis in criminal proceedings of increased complexity. The article analyzes procedural and non-procedural forms of a specialist’s participation in criminal proceedings, in particular his involvement in investigative (search) actions, consultations, and the preparation of reports and conclusions. The specifics of the activities of interdepartmental working groups of military specialists who perform complex tasks of reconstructing events in the context of an armed conflict, analyzing the use of weapons, and establishing the role of specific individuals in the mechanism of the crime are revealed. It has been proven that such groups function as an integrated mechanism for forensic support during the investigation. The participation of specialists in the review of computer data from open sources, which ensures the recording, verification, and interpretation of information from open sources, is separately studied. It is substantiated that such activities are a necessary condition for their procedural admissibility.