One important aspect of counter-terrorism is gathering information for intelligence. In counter-terrorism it could be useful to interview suspects without them being aware that they are interviewed or interviewing may not even be possible, giving investigators no option other than to observe suspects. Most forensic lie detection research to date concentrates on police/suspect interviews. A consistent finding in deception research is that liars prepare themselves when anticipating an interview. An investigator could exploit the differential levels of cognitive load that truth-tellers and liars experience to discriminate more effectively between them. In the Strategic Use of Evidence technique the investigator aims to detect these differential strategies via a strategic use of the available evidence, which may include possible incriminating information. A consistent finding in deception research is that liars prepare themselves when anticipating an interview. To test the unanticipated questions technique, pairs of liars and truth-tellers were interviewed individually about an alleged visit to a restaurant.