The article provides a thorough study of the classification and tactical potential of sources for obtaining forensically significant information used during the investigation of grave and especially grave crimes. The relevance of the topic is driven by the transformation of crime in the context of global digitalization, where traditional methods of evidence collection face new challenges: the remote nature of actions, data encryption, and professional counteraction to the investigation. The aim of the work is to systematize existing information sources and identify new ones to increase the efficiency of solving the most dangerous offenses. A complex of methods was used in the research process: systemic-structural analysis allowed for the consideration of the investigative information environment as an integrated system; the comparative-legal method helped to compare procedural and orienting data; and the classification method served as the basis for grouping sources by the nature of the carrier, stability, and accessibility. Research results consist in the development of an expanded classification of information sources. The author provides a detailed analysis of not only traditional (material and ideal) but also non-traditional sources: Internet of Things data, smart home systems, biometric and geolocation patterns, as well as digital footprints in the media space. Particular attention is paid to behavioral sources, which allow for the reconstruction of the offender’s psychological profile and the prediction of their further actions. It is proved that the successful investigation of grave crimes is possible only through the integration of traditional forensic tools with the latest digital technologies. It is determined that the tactical significance of each source depends on its stability: unstable information (digital and olfactory) requires immediate recording. The systemic use of the proposed classification allows investigators to avoid fragmentation in data collection, ensures a proper evidentiary base, and contributes to overcoming active counteraction by organized criminal groups. The scientific novelty lies in a comprehensive approach to combining material, procedural, and analytical information sources into a single investigative algorithm.