<p>In stab wounds, the knife is a central carrier of biological traces, whose recovery, analysis, and interpretation can contribute to reconstructing the course of events. Classically, forensic DNA analysis focuses on the sub-source level—that is, attributing adherent trace material to individuals. In complex cases, however, this individualization alone is insufficient to clarify the context of origin or to evaluate competing activity hypotheses regarding the knife. Modern forensic molecular biological approaches therefore extend trace interpretation to include a source level and an activity level. RNA-based body fluid/tissue identification allows differentiation of which tissues (e.g., blood, skin, cardiac, hepatic, or skeletal muscle) are adhering to a knife blade—and thus what type and severity of injury is likely present. This facilitates distinguishing, for example, between defensive cut wounds, everyday injuries, and targeted stab wounds. At the activity level, the focus shifts to DNA transfer. Set against highly sensitive analytical methods stands the dependence of DNA transfer on numerous variables, meaning the question of how a person’s DNA came to be on a knife handle can only be answered &#xa0;evidence-based at the activity level. Drawing on experimental studies of transfer, prevalence, persistence, and recovery of DNA, as well as international guidelines for DNA evidence evaluation, the article discusses what statements can be made regarding competing activity hypotheses—and where the limits of such statements lie. The paper argues for the systematic recovery and examination of biological traces on knives through the integration of the sub-source, source, and activity levels.</p>