This study is on how to discriminate between true and false intentions, an emerging area within psycholegal research. We argue that asking about the past (the planning phase) might be a promising way to detect lies about the future (intentions). That is, participants who had developed false intentions to mask their criminal intentions were assumed to provide equally long and detailed answers to questions about intentions, compared to participants who told the truth about their intentions. In contrast, we predicted that lying participants would be worse at answering questions about the planning of their stated (false) intentions, compared to participants telling the truth about the planning of their stated (true) intentions. To test our assumptions, we used a newly devised experimental set-up accommodating the main characteristics of intent. Both lying and truth-telling suspects perceived the questions on planning as more unanticipated, and more difficult to answer, compared to the questions about their intentions (future actions). Furthermore, in support of our predictions we found that the truth-telling (vs. lying) suspects' answers to questions on planning were longer and perceived as more detailed and clear, whereas liars' and truth-tellers' answers to questions on intentions were equally long and perceived as equally detailed.