Sham marriages occur frequently and, to detect them, partners are sometimes interviewed together. We examined an innovative method to detect deceit in such interviews. Fifty‐three pairs of interviewees, either friends (truth tellers) or pretended to be friends (liars), were interviewed about their friendship. Just before the interview, they received the questions that would be asked in the interview and were invited to prepare the answers. We told them that these pre‐interview deliberations would be recorded. Based on the transcripts we analysed cues to truthfulness (cues expected to be expressed more by truth tellers) and cues to deceit (cues expected to be expressed more by liars). Truth tellers and liars differed from each other, particularly regarding expressing cues to truthfulness. Pre‐interview deliberations that are recorded with awareness of the interviewees can be used for lie detection purposes. We discuss further venues in this new line of research.