Abstract: The author analyzes the situations when investigators work among accomplices in crime. The author analyzes the problems of criminal law and legal regulation of investigative activities. The author considers acceptable, to his opinion, variants of behavior correlating with the signs of various types of accomplices of crime. Special attention is given to the concept of “participation” in various criminal groups as a feature of objective side of compositions of crimes. The author gives examples from the published judicial practice relating to the topic of the research. The author’s conclusions and suggestions can be used for the application of the criminal law and in investigative activities. The author uses the dialectical method of cognition, which allows reflecting the interrelation between theory and practice, and the methods of qualitative analysis of social and legal processes, content-analysis, documents study, expert assessments, surveys, etc. The scientific novelty of the study consists in complex intersectoral analysis of problems of legal regulation of investigation within criminal environment. The author makes a hypothesis that it is possible to consider actions, which are seemingly alike the behavior of a perpetrator of crime or an accomplice, as rightful. The author substantiates the possibility to act like a perpetrator, instigator, organizer or leader.