The paradigmatic finding from research on deception detection is that people are poor at discriminating between liars and truth tellers. This research paper shows, however, that deception detection performance can be significantly improved if the investigator is allowed to interview the suspect, is given background information about the case and the suspect, and knows how to strategically use this background information (evidence) when conducting the interview. This research paper contains a description of the psychological basis for the so-called Strategic Use of Evidence (SUE) technique and also explains what it means to strategically use evidence during an interview.
The research conducted to date on the issue of strategic use of evidence to detect deception shares two important features. First, it is based on a mock-crime paradigm, where half the participants commit a mock crime and the other half commit a noncriminal act. Second, for each suspect there is some potentially incriminating information indicating his or her guilt, but this information does not preclude that the suspect is in fact innocent. The interviewers were different for different studies: experienced police officers, police trainees, and trained experimenters.
This line of research is primarily motivated by three facts. First, there is often some information (evidence) pointing to the guilt of the person who becomes a suspect in a criminal investigation. Second, the so-called interview and interrogation manuals have very little to offer in advising how to best use this potentially incriminating information when interviewing a suspect. Third, both archival and field experiments show that many investigators tend to use the potentially incriminating evidence in a nonstrategic manner.
The SUE technique rests on the psychology of guilt and innocence. It has been found that it is significantly more common among guilty than innocent suspects to bring a strategy to the interview room. Research further shows that with respect to the strategies used during an interview, guilty and innocent suspects differ markedly. Specifically, guilty suspects will—if given the opportunity—avoid mentioning possibly incriminating information during an interview and—if deprived of the avoidance alternative—deny that they hold incriminating knowledge. Both these findings fit neatly with what is known of some of the most basic forms of human behavior—namely, aversive conditioning. That is, research on aversive conditioning has found an avoidance response (so as to try to prevent confrontation with a threatening stimulus) and an escape response (so as to try to terminate a direct threat).
In sharp contrast, research on the behavior and cognition of innocent suspects shows that they do not tend to avoid and escape the potentially incriminating information. Instead, their main strategies seem to be “to keep the story real” and “to tell the truth like it happened.” In short, they trust the truth to shine through. This is in accord with well-established cognitive biases such as the belief in a just world (i.e., people will get what they deserve and deserve what they get) and the illusion of transparency (one’s inner feelings will manifest themselves on the outside).
The fact that guilty and innocent suspects employ different strategies can be very useful for the investigator who needs to assess the veracity of the statement offered by a particular suspect, if he or she knows how to use the existing evidence strategically. In essence, the investigator should first use the case file to identify pieces of potentially incriminating information, place extra weight on information that the suspect will not know for certain that the investigator possesses, and then prepare questions addressing the potentially incriminating information. In its most basic form, the SUE technique proposes that when conducting the actual interview, the investigator should encourage the suspect to give a free recall—without disclosing any of the potentially incriminating information to the suspect—and then ask questions, of which some address the potentially incriminating information, still without revealing what the investigator knows.
If the potentially incriminating information is used in a strategic manner, as suggested by the SUE-technique, then two predictions can be made: First, guilty suspects will deliver a statement that, on one or several occasions, contradicts what the interviewer knows. That is, it will be possible to identify statement-evidence inconsistencies. Second, innocent suspects can be expected to tell a story consistent with what the interviewer knows. That is, there will be a high degree of statement-evidence consistency. Importantly, both these predictions have received empirical support.
A training study using highly motivated police trainees showed that the ones who received training in how to use the evidence strategically during an interview achieved a significantly higher deception detection accuracy (85%) than did the ones who received no such training (56%). By interviewing in accordance with the SUE technique, the trained interviewers managed to both create and use a diagnostic cue to deception—namely, statement-evidence inconsistency. In addition, for trained interviewers it was found that innocent suspects experienced much less cognitive demand than guilty suspects (which is a positive finding), whereas for untrained interviewers it was found that innocent and guilty suspects did not differ in terms of cognitive demand (which is a negative finding).
In sum, if interviewers learn to strategically use potentially incriminating information, they will enhance their ability to detect deception and truth. In essence, the SUE technique works because it draws on the psychology of guilt and innocence and, particularly, the striking heterogeneity in guilty and innocent suspects’ strategies. The SUE technique is not a confrontational interrogation technique; it instead belongs to the information-gathering techniques. However, the key factor is not the amount of information gathered as such but to draw on the differences in information that innocent suspects volunteer and guilty suspects avoid and escape from providing.
- Hartwig, M, Granhag, P. A., Stromwall, L. A., & Kronkvist, O. (2006). Strategic use of evidence during police interviews: When training to detect deception works. Law and Human Behavior, 30, 603-619.
- Hartwig, M., Granhag, P. A., Stromwall, L. A., & Vrij, A. (2005). Detecting deception via strategic disclosure of evidence. Law and Human Behavior, 29, 469-484.
- Kassin, S. M. (2005). On the psychology of confessions: Does innocence put innocent at risk? The American Psychologist, 60, 215-228.