This article reports on a study into epistemic strategies used in the trial on the 2010 Polish Air Force Tu-154 air crash which took the lives of many high-ranking Polish officials including the President of Poland. It follows the KUB model proposed by Bongelli and Zuczkowski (2008), in which three epistemic stances are distinguished: Knowing, Unknowing and Believing. Taking into account the political context of the trial, the study focuses on the ways in which the witness, Poland’s former Prime Minister Donald Tusk, communicates his knowledge (certainty), unknowledge (neither certainty nor uncertainty) and belief (uncertainty). As the data reveal, when referring to the circumstances of the crash itself, the witness most willingly communicates unknowledge and belief while his declarations of certitude (knowledge) concern mostly procedural matters which are not directly related to the crash. As regards the explicit marking of (un)knowledge with the verb wiedzieć (‘know’), both wiem (‘I know’) and nie wiem (‘I don’t know’) are used rather sparingly. By contrast, phrases including references to the witness’s memory (e.g. to, co mam w pamięci [‘what I can remember’]) – marking either unknowledge or limited/uncertain knowledge (belief) – resurface as the witness’s preferred strategy. The data also demonstrate frequent co-occurrences of ‘knowing,’ ‘unknowing’ and ‘believing’ markers, reducing the overall degree of certainty communicated by the speaker. In sum, the study reveals how Poland’s former Prime Minister skillfully avoids unequivocal or categorical answers and conveys a low degree of certainty in his testimony.