How to Detect Deception? Arresting the Beliefs of Police Officers, Prosecutors and Judges

In this paper we examined beliefs about deception held by legal professionals. Three groups of presumed expert lie-catchers were investigated: police officers ( n =104), prosecutors ( n =158), and judges ( n =251). The experts' beliefs about deception were remarkably inconsistent with the general pattern resulting from studies mapping actual cues to deception. For example, a majority of police officers believed there is a strong relationship between (a) deceptive behaviour and gaze aversion and (b) deceptive behaviour and an increase in body movements. The scientific literature does not support this view. Furthermore, all three professional groups believed that truthful consecutive statements are more consistent than deceptive, and that it is easier to detect deception in interactive than non-interactive contexts. Research on deception shows the opposite. For five of the seven investigated items we found significant between-group differences. Both the genesis and the implications of these differences are discussed. Judging from self-ratings, the presumed experts admitted knowing close to nothing about scientific research on deception.

Survey-based study using a questionnaire covering seven key deception-related items administered to 104 police officers, 158 prosecutors, and 261 judges in Sweden, comparing their beliefs to established research findings.

Strömwall and Granhag investigated whether Swedish legal professionals possessed accurate knowledge about deception detection cues. Using a questionnaire based on established scientific literature, they surveyed 523 active criminal justice professionals across three groups. Results showed that majorities of police officers incorrectly believed in gaze aversion and increased body movement as deception indicators, contrary to research findings. All three groups incorrectly believed deceptive statements are less consistent than truthful ones and that interrogators are more accurate than observers. The study revealed significant between-group differences on five of seven items and highlighted that professionals self-rated themselves as having minimal knowledge of scientific deception research despite making critical credibility judgments.

These findings demonstrate that professional training and decision-making in criminal justice are not grounded in empirical evidence about deception detection, creating risk for wrongful convictions and acquittals. The study underscores the urgent need for reform in training standards, professional certification requirements, and evidence-based guidelines for how legal professionals should approach deception assessment in criminal proceedings.

Background & Context

The ability to detect deception is fundamental to criminal justice, yet questions persist about whether legal professionals possess accurate knowledge about what actually distinguishes truth from lies. This 2003 study by Strömwall and Granhag addresses a critical gap: the mismatch between what police, prosecutors, and judges believe about deception cues and what scientific research actually shows.

Published during a period of growing scientific skepticism about traditional deception detection methods, this research emerged as courts and law enforcement increasingly relied on behavioral assessments during investigations and trials. The stakes could not be higher—faulty beliefs about deception cues can lead to wrongful convictions of innocent people displaying nervous behavior, or acquittals of skilled liars who control their demeanor.

Prior to this study, limited research had systematically examined whether the very professionals tasked with judging credibility actually understood the scientific literature on deception. The findings would prove both eye-opening and concerning for the criminal justice system.

Research Design & Methodology

The study surveyed 523 criminal justice professionals in Sweden, including 104 police officers (38 women and 64 men), 158 prosecutors (61 women and 97 men), and 261 judges (59 women and 190 men). This large sample represented individuals actively making deception judgments in real forensic contexts.

Researchers developed a questionnaire based on previous deception research covering seven key items: details provided, gaze behavior, consistency of consecutive statements, body movements, voice pitch, whether interrogators or observers are more accurate in detecting deception, and whether verbal or nonverbal cues are more reliable. Respondents provided their opinions on forced-choice answer scales regarding the importance of each item in detecting deception.

The questionnaire was specifically designed to test whether professionals' beliefs aligned with empirical findings from the scientific literature. Participants also self-rated their knowledge of scientific deception research, providing insight into their awareness of the evidence base.

Results & Key Findings

The findings revealed that all three professional groups held beliefs about deception detection that were remarkably inconsistent with scientific research. The disconnect between belief and reality was stark across multiple deception cues.

Key misconceptions identified:

• The majority of police officers believed that liars display more gaze aversion than truth-tellers, yet research shows no relationship between gaze aversion and deception
• The majority of police officers believed there is an increase in body movements during deception, but research demonstrates that liars often have less body movement than truth-tellers
• All professional groups strongly believed that deceptive consecutive statements are less consistent than truthful ones, when previous research found that deceptive statements are at least equally consistent compared with truthful statements
• All three groups believed that interrogators are more accurate at detecting deception than those who observe videotaped interviews, when research shows the opposite

For five of the seven investigated items, researchers found significant between-group differences among the professional categories. Perhaps most troubling, when judging from self-ratings, the presumed experts admitted knowing close to nothing about scientific research on deception.

Discussion & Significance

This study exposed a profound gap between professional practice and scientific evidence in deception detection. The findings suggest that legal professionals rely heavily on intuitive folk theories about lying—beliefs likely shaped by cultural stereotypes and training materials disconnected from empirical research.

The reliance on nonverbal cues like gaze aversion and body movements is particularly problematic because these behaviors can indicate nervousness, cognitive load, or cultural communication patterns rather than deception. Innocent suspects under the stress of interrogation may display these exact behaviors, leading to systematic misattribution errors.

The study aligns with broader deception detection literature, including DePaulo et al.'s (2003) meta-analysis showing most nonverbal behaviors have weak or non-existent relationships with deception. The disconnect between professional beliefs and scientific evidence helps explain why detection accuracy in forensic contexts often hovers near chance levels.

The authors emphasized that given the influence such beliefs have on investigation, processing, and case outcomes, it is critical that researchers disseminate their findings to professions whose beliefs and decisions impact justice.

Limitations & Considerations

The study examined beliefs through self-report questionnaires rather than observing actual deception detection performance in live cases. While beliefs about cues are important, they may not perfectly predict how professionals actually make credibility judgments when facing real suspects or witnesses.

The sample consisted exclusively of Swedish legal professionals. Cultural factors may influence both beliefs about deception and actual deception behaviors, potentially limiting generalizability to other legal systems. However, subsequent international research has found remarkably similar misconceptions across cultures.

The questionnaire focused on specific deception cues identified from research literature. Professionals may use additional contextual information, evidence consistency, or case-specific factors not captured in the survey when making real-world credibility assessments.

Practical Applications

This research has profound implications for training and professional development in law enforcement and legal practice. The findings suggest that current training programs may be perpetuating myths rather than teaching evidence-based deception detection strategies. Police academies and continuing legal education should incorporate up-to-date scientific research on what actually distinguishes truth from deception.

For consumers facing polygraph examinations or credibility assessments, this study reveals why behavioral symptoms of nervousness should not be automatically interpreted as deception. Understanding that even experienced legal professionals hold misconceptions about deception cues can help examinees recognize when they may be unfairly judged based on anxiety, neurodivergence, or cultural communication differences rather than actual dishonesty.