The article addresses the issues of lawyer's investigation and evidence gathering in criminal cases involving technological disasters. The authors analyze the specific nature of proof in this category of cases, determined by the gap between technical and legal causality, the multiplicity of liable parties, and the necessity to use civil law documents (insurance contracts, certificates of conformity, service contracts, instructions of supervisory authorities, industrial safety declarations, etc.). The legal nature of lawyer's investigation, its role in the mechanism of criminal proceedings, as well as procedural and tactical problems of attaching documents collected by the lawyer to the criminal case materials are examined. Proposals for improving legislation aimed at enhancing the effectiveness of lawyer's investigation and ensuring genuine adversariality in criminal proceedings involving technological disasters are formulated.