Approximately 8,000 boys and men were killed in the 1995 Srebrenica genocide. The victims were disappeared, killed and buried in secret mass graves. In this article, I examine how forensic anthropologists, demographers and forensic geneticists produced technolegal knowledge about the number of victims in the wake of the genocide; how those numbers were validated in legal proceedings against those held responsible; and, finally, how some have tried to destabilize the numbers in attempts to deny that a genocide was committed. While numbers, and the larger category of knowledge, take centre stage in the discussion, I use Srebrenica’s aftermath to introduce the concept of ontologically dirty knots, which is an analytical and methodological innovation that enables us to produce scholarly accounts of events, such as the Srebrenica genocide, that are characterized partly by secrecy, partly by controversy and partly by materiality. It ties together meaning and materiality, signals a process that continues to evolve, and suggests that narratives about what happened are the results of entanglements, action and friction that can be undone. In these respects, the article addresses current discussions on actor-network theory within critical security studies.