This study focused on the Guilty Knowledge Test (GKT) - a psychophysiological detection method based on a series of multiple-choice questions, each having one relevant and several neutral (control) alternatives. The study examined a new method designed to reduce false-positive outcomes due to leakage of relevant items to innocent suspects by introducing target items (i.e., items known to all examinees but unrelated to the crime) to which participants have to respond (e.g., by pressing a key) while answering the GKT questions. Informed innocent participants showed relatively larger electrodermal responses to the critical items than uninformed participants, but not as large as the responses made by guilty participants. No differences between informed and uninformed innocent participants were obtained with a respiration measure. The use of the target items tended to reduce the differences between informed and uninformed innocent participants. The results further demonstrated that electrodermal responding to the relevant items was correlated with memory of these items.