This case study is based on a transcript of an authentic criminal proceeding in a Belgian Assize Court, where Dutch is the official language and the French-speaking defendant receives simultaneous whispered interpretation of the prosecutor’s closing speech. Examining six excerpts from the speech, which is addressed to the judges and the lay jury, the analysis compares the Dutch original with the French interpretation. The specific focus of the study is the Aristotelian concept of ethos, i.e. the image the speaker seeks to convey of himself by foregrounding his professional expertise, integrity and goodwill towards the audience. Since the rhetorical devices he uses for this purpose are often absent from the interpretation in the extracts analysed, the strategic persuasiveness of his speech is weakened. This means that the defendant is likely to gain an incomplete, misleading perception of his own case. In the light of the examples presented here, the authors argue that the theory of classical rhetoric affords a useful framework for exploring interpreter-mediated legal monologues in a dialogical perspective.