The article examines the challenges in detecting features of verbal extremism by analysing forensic practice, research papers on forensic linguistics and anti-extremist law, manuals developed by Russian law enforcement agencies and scientific and educational organizations. The article suggests a new approach to the methodological support of forensic linguistic examination of extremist discourse. This approach is based on the concept of a three-component structure of ‘extremist’ utterances. The author justifies the proposed classification of extremist speech acts and describes forensic diagnostic complexes corresponding to these speech acts. These complexes can serve as the reference samples for both linguistic experts (who conduct forensic examination) and the law enforcement officers (who conduct forensic diagnostics). The use of standardized forensic diagnostic complexes of extremist speech acts which serve as a tool for classification of illegal verbal behaviour allows to maintain the balance between the right to freedom of speech and pluralism of opinions, on the one hand, and protection against abuse of these rights (protection of media security), on the other hand.