Effective investigation of criminal offenses committed in the field of professional legal aid requires a scientifically sound, systematically constructed forensic methodology that accounts for the complexity of this category of crimes, their latent nature, and the specificity of the subject. The aim of the article is to provide a theoretical justification for the forensic methodology for investigating criminal offenses in the context of professional legal aid and to develop an optimal model for its construction, taking into account modern challenges in law enforcement practice. The article notes that an effective methodology should be built as a multi-level system that combines specific methodologies, generalizes them, and details them through micromethodologies. It is substantiated that its structure should include the forensic characteristics of the crime, circumstances subject to proof, typical investigative situations, and action algorithms, organizational and planning aspects of the investigation, tactical features of conducting investigative (search) actions, measures to overcome counteraction, use of special knowledge, and a preventive component. It is stated that the proposed approach ensures the systematicity, adaptability, and practical orientation of the forensic methodology and creates a basis for increasing the efficiency of the pre-trial investigation.