This article centres on an unconventional figure. Tadeusz Cyprian (1898–1979) was not only an outstanding lawyer but also a talented photographer. He contributed to the documentation of nazi crimes during WW2. Cyprian was a prosecutor before the Supreme National Tribunal (Najwyższy Trybunał Narodowy), and one of the four Polish delegates at the Nuremberg Trials. My investigation concerns the issue of responsibility for crimes committed by the Germans during WW2 from the perspective of Cyprian as prosecutor and as photographer. Illustrations loom large in the article, and still more so in the whole study, given the aims of the research. The research method that is presented here is not often used by lawyers for methodological reasons. Yet law is not a system detached from external reality. Legal research and the interpretation of the law should be conducted in an interdisciplinary way. My article is divided into four parts: (1) the theoretical and contextual framework; (2) key episodes in Cyprian's biography; (3) the dispensing of justice in Poland; and (4) the individual behind the legal principle of the punishment and prevention of genocide. The value of the first part consists, inter alia, in its highlighting of the importance of interdisciplinary research. This is especially relevant for legal biographical studies, for examining the functioning of a specific court, for its judges and for the specific category of trials.