This article focuses on the use of expert knowledge as a basis for legal decisions in serious criminal cases. Using a model that describes rhetorical situations, as well as empirical material based on 150 court decisions, the aim is to analyse the conditions surrounding the use of expert evidence in criminal law processes, to what extent and by whom such evidence is used, and how it affects the outcome of the cases. The rhetorical situation in criminal cases is reconstructed to include the exigence (urgent issue that requires addressing) and, thereby, the related discourse, in order to retrieve relevant conditions, which could be identified as evidentially favourable or unfavourable to the suspect and the prosecutor respectively. It is conc...