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Detecting deception is an inherently difficult task, but one that plays a critical role for law enforcement investigators in the interrogation room. In general, research has failed to indicate that performance in this domain is improved by training or prior experience. A signal detection framework is applied to the paradigm to better conceptualize the influence of these two factors. We found that although neither factor influenced discrimination accuracy, there was an effect on response bias such that training and prior experience appeared to increase the likelihood of responding "deceit" as opposed to "truth." This "investigator bias" was observed both in a review of the literature and in this study of North American law enforcement investigators who took part in a forensically based deception-detection task. Possible theoretical mechanisms and practical implications of these findings are discussed.
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Law and Human Behavior [lahu] pp614-lahu-450951 September 4, 2002 20:33 Style file version June 4th, 2002
Law and Human Behavior, Vol. 26, No. 5, October 2002 (
“He’s guilty!”: Investigator Bias in Judgments
of Truth and Deception
Christian A. Meissner
and Saul M. Kassin
Detecting deception is an inherently difficult task, but one that plays a critical role for
law enforcement investigators in the interrogation room. In general, research has failed
to indicate that performance in this domain is improved by training or prior experience.
A signal detection framework is applied to the paradigm to better conceptualize the
influence of these two factors. We found that although neither factor influenced dis-
crimination accuracy, there was an effect on response bias such that training and prior
experience appeared to increase the likelihood of responding “deceit” as opposed to
“truth.” This “investigator bias” was observed both in a review of the literature and in
this study of North American law enforcement investigators who took part in a foren-
sically based deception-detection task. Possible theoretical mechanisms and practical
implications of these findings are discussed.
KEY WORDS: deception; interrogation; response bias.
Police-induced confessions are a potent prosecutorial weapon that can have far-
reaching and rippling effects on the disposition of cases and on the criminal jus-
tice system as a whole. Indeed, modern police interrogations are so powerful that
they have, at times, elicited coerced-compliant and -internalized false confessions
from innocent people (Gudjonsson, 1992; Kassin, 1997; Leo & Ofshe, 1998; Radelet,
Bedau, & Putnam, 1992; Scheck, Neufeld, & Dwyer, 2000). Research suggests that
the process of interrogation is persuasive, if not too persuasive, in part because
it is explicitly based upon a presumption of guilt—an assumption that itself can
set in motion a number of cognitive and behavioral confirmation biases (Kassin,
Goldstein, & Savitsky, 2001). As described by Inbau, Reid, Buckley, and Jayne (2001)
Portions of this paper were presented at the 2002 American Psychology–Law Society Conference in
Austin, TX.
Department of Psychology, Florida International University, Miami, Florida.
Department of Psychology, Williams College, Williamstown, Massachusetts.
To whom correspondence should be addressed at Department of Psychology, Florida International Uni-
versity, University Park, Miami, Florida 33199; e-mail: or Department of Psychology,
Williams College, Williamstown, Massachusetts 01267; e-mail:
2002 American Psychology-Law Society/Division 41 of the American Psychology Association
Law and Human Behavior [lahu] pp614-lahu-450951 September 4, 2002 20:33 Style file version June 4th, 2002
470 Meissner and Kassin
in their manual, Criminal Interrogation and Confessions, An interrogation is con-
ducted only when the investigator is reasonably certain of the suspect’s guilt” (p. 8).
Justifying the use of heavy-handed tactics, many law enforcement professionals
believe that they can determine whether a suspect is being truthful or deceptive on
the basis of a preinterrogation interview during which a suspect is questioned in a
nonconfrontational manner about his or her knowledge, whereabouts, and possible
involvement in the crime. Furthermore, many believe that they can learn to make
these initial judgments at high levels of accuracy by observing various aspects of the
suspect’s verbal and nonverbal behavior (Inbau et al., 2001; Vessel, 1998). According
to John E. Reid and Associates, for example, investigators trained in their Behavior
Analysis Interview are able to distinguish truth and deception at an 85% level of
accuracy (
Unfortunately, psychological research has generally failed to support the claim
that individuals can attain high levels of performance in making judgments of truth
and deception. Over the years, numerous studies have demonstrated that individuals
perform at no better than chance level in detecting deception (DePaulo, Stone, &
Lassiter, 1985), that training programs produce only inconsistent improvements in
performance compared with control conditions (Bull, 1989; Kassin & Fong, 1999;
Porter, Woodworth, & Birt, 2000; Vrij, 1994; Zuckerman, Koestner, & Alton, 1984;
Zukerman, Koestner, & Colella, 1985), and that police investigators and others
with relevant on-the-job experience perform only slightly better, if at all (Bull,
1989; DePaulo, 1994; DePaulo & Pfeifer, 1986; Ekman & O’Sullivan, 1991; Ekman,
O’Sullivan, & Frank, 1999; Koehnken, 1987; Porter et al., 2000). Thus, although many
in the law enforcement community assume, often with great confidence, that inves-
tigators can use verbal and nonverbal behavioral cues to make accurate judgments
of truth and deception, there is little hard evidence to support this assumption.
Unfortunately, the implications of falsely inferring deceit in the interrogation
room can be quite costly to an innocent suspect. Consider, for example, the mili-
tary trial of U.S. v. PFC Timothy Bickel (1999), in which one of us testified as an
expert witness (the second author). In this case, a confession to rape was extracted
by a combination of five agents who used persistent and highly aggressive techniques
(e.g., explicit and implied promises and threats, negative feedback on a polygraph
test that was described as infallible, and the use of minimization) despite the ab-
sence of independent evidence against the defendant. When asked why they chose
to interrogate Bickel and not others, one investigator noted that he showed “signs
of deception based on the training we have received. More specifically, this inves-
tigator stated, “His body language and the way he reacted to our questions told us
that he was not telling the whole truth. Some examples of body language is that he
tried to remain calm but you could tell he was nervous and every time we asked
him a question his eyes would roam and he would not make direct contact, and at
times he would act pretty sporadic and he started to cry at one time. Correctly, we
believe, this defendant was acquitted at trial. There are many other instances too,
such as the case of Tom Sawyer, in Florida, in which investigators accused the de-
fendant of sexual assault and murder, interrogated him for 16 hr, issued threats, and
extracted a confession likely to have been false (cited in Ofshe & Leo, 1997). The
confession was suppressed by the trial judge, and, in the absence of other evidence,
Law and Human Behavior [lahu] pp614-lahu-450951 September 4, 2002 20:33 Style file version June 4th, 2002
Investigator Bias 471
the charges were dropped. Most intriguing to us was the manner in which Sawyer
became a prime suspect—his face flushed and he appeared embarrassed during an
initial interview, a behavioral reaction interpreted as a sign of deception. However,
what the investigators did not know was that Sawyer was a recovering alcoholic with
a social anxiety disorder that caused him to sweat profusely and blush in evaluative
social situations.
Given the profound implications for error at this early stage of criminal investi-
gations, it is important to understand the influence of training and prior experience
on the deception-detection performance of police investigators. Regrettably, how-
ever, a quick survey of the literature may itself prove somewhat deceptive, as many
studies have reported only global accuracy rates (i.e., percentage correct) across
all targets. We believe that such a method of analysis may fall short of provid-
ing a complete account of the performance of individuals as a function of lev-
els of experience or training. Rather, considering the influence of such manipu-
lations across both truthful and deceitful targets would allow greater insight into
processes underlying deception-detection decisions, particularly when placed within
the context of signal detection theory (SDT; Green & Swets, 1966; MacMillan &
Creelman, 1991). Unfortunately, in only a few cases have researchers actually pro-
vided such estimates of truthful and deceitful performance (Ekman et al., 1999;
Kassin & Fong, 1999; Porter et al., 2000; Vrij, 1993; Vrij & Mann, in press), and
in no cases have researchers directly applied SDT to assessing deception-detection
Although it is possible that training or experience may increase an individual’s
ability to discriminate between truthful and deceptive target persons, it may alter-
natively bias decisions toward truth or deceit on the basis of a variety of factors. As
conceived by Green and Swets (1966), SDT provides a framework for separating
performance into two conceptually and computationally independent parameters,
namely discrimination accuracy—the ability of an individual to correctly detect a
signal (deception) versus correctly reject its absence (truth), and response bias—the
degree of evidence necessary for the individual to respond that a signal (decep-
tion) has been presented. Although SDT has been widely used throughout psychol-
ogy, as in the study of decision making among air-traffic controllers, doctors, and
clinical psychologists, it has not been applied to the study of deception-detection
judgments (but see Thompson, 1978, regarding the detection of social cues). The
implication is that various targets, expectations, experiences, and other manipula-
tions thus far presented in the deception literature may differentially influence the
two SDT parameters. Knowing how these parameters are influenced should also
provide insight into the nature of the psychological effects underlying the various
With regard to the effects of training or prior experience, proponents seem to
suggest that certain manipulations would only influence discrimination accuracy by
enhancing one’s ability to correctly differentiate truth from deceit. This certainly
represents the aim of most training methods that seek to provide knowledge of
verbal and nonverbal cues inherent in deception. On the basis of the relative in-
dependence of the two SDT parameters (cf. Snodgrass & Corwin, 1988), it may
also be assumed that training and experience would not influence the response
Law and Human Behavior [lahu] pp614-lahu-450951 September 4, 2002 20:33 Style file version June 4th, 2002
472 Meissner and Kassin
bias parameter, that is, the individual’s tendency to overly respond “truth” versus
We first evaluated this hypothesis by conducting a brief survey and reanalysis
of existing research. In particular, we looked for studies that examined the influence
of either experience, such as law enforcement, or specific training in the detection of
deception. Our literature search was constrained by the requirements that studies
(a) report accuracy for both truthful and deceitful targets and (b) include a no-
training or no-experience control condition. For studies in which only gross accuracy
estimates were reported, authors were contacted for the additional relevant infor-
mation. Overall, we were able to locate four studies that examined the influence of
prior experience (Chahal & Cassidy, 1995; DePaulo & Pfeifer, 1986; Ekman et al.,
1999; Porter et al., 2000) and two that assessed the influence of training on deception-
detection performance (Kassin & Fong, 1999; Koehnken, 1987). Together, these six
studies represented the responses of 1,161 participants. Other studies were excluded
either because of insufficient reporting of data (deTurck , 1991; deTurck & Miller,
1990; Ekman & O’Sullivan, 1991; Kraut & Poe, 1980; Vrij, 1994; Zukerman et al.,
1984, 1985) or because they did not include a control condition (Vrij, 1993; Vrij
& Graham, 1997; Vrij & Mann, 2001). A studywise SDT analysis (MacMillan &
Creelman, 1990; MacMillan & Kaplan, 1985) was performed on the performance
means that were either reported in the paper or provided by the authors. Estimates
of hits (i.e., the proportion of deceptive persons correctly identified as such) and false
alarms (i.e., the proportion of truthful persons incorrectly identified as deceptive)
were used to compute studywise SDT estimates of both discrimination accuracy (A
and response bias (B
) for each condition (see Donaldson, 1992). Finally, the differ-
ence in performance between the experimental and control conditions was computed
by estimating the variance for each SDT parameter and computing Cohen’s d effect
size (see Rosenthal, 1994). Positive effect sizes for A
would indicate that participants
in the experimental condition (trained or experienced) outperformed the controls,
whereas positive effect sizes for B
would indicate that participants in the experi-
mental condition exhibited a more conservative response bias (i.e., higher likelihood
of responding “truthful” across all cases) than did controls.
Studywise estimates of discrimination accuracy (A
), response bias (B
), and ef-
fect size (Cohen’s d) are presented in Table 1. Across studies, the average weighted
effect size for the A
measure was Cohen’s d =−0.129, a non-significant effect size,
z = 1.92, with confidence intervals (0.261, 0.003). In contrast, the B
D weighted
effect size was significant, Cohen’s d =−0.317, z = 4.75, p <.001, with confidence
intervals (0.448, 0.186). Thus, across studies, both training and prior experience
engendered a more liberal response criterion (i.e., a bias toward responding “deceit-
ful”) when compared to participants in the no-training and no-experience control
conditions. In contrast to what one might have expected, however, training and ex-
perience had no significant effect on participants’ ability to accurately discriminate
truth from deceit.
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Investigator Bias 473
Table 1. Estimates of Signal Detection Performance (A
and B
) and Effect Sizes (Cohen’s d ) for the
Influence of Experience or Training in a Deception-Detection Task
Study Manipulation NMCohen’s dMCohen’s d
Porter et al. (2000) Control vs. parole officers 32 vs. 32 0.31 0.867 0.02 1.050
0.10 0.60
Ekman et al. (1999) Control vs. police officers 425 vs. 105 0.70 0.005 0.04 0.342
0.69 0.24
DePaulo & Pfeifer (1986) Control vs. police officers 161 vs. 258 0.59 0.187 0.47 0.208
0.54 0.35
Chahal & Cassidy (1995) Control vs. social workers 40 vs. 20 0.75 0.041 0.16 0.576
0.73 0.18
Kassin & Fong (1999) Na¨ıve vs. trained 20 vs. 20 0.63 0.451 0.14 0.547
0.52 0.18
Kohnken (1987) Na¨ıve vs. trained 20 vs. 60 0.41 0.159 0.60 0.203
0.37 0.48
Our effect size analysis of the existing literature yielded an investigator bias ef-
fect, suggesting that training and prior experience lead to a perceptual bias toward
judgments of deceit. As this result was unexpected, and as previous studies had nei-
ther computed signal detection parameters nor predicted (a priori) such a finding,
we attempted to assess directly the validity of this investigator bias in a sample of
law enforcement officers. We also sought to extend the ecological validity of the
deception-detection task to more closely match the kinds of forensic judgments that
investigators routinely make. Of the studies that were included in our studywise anal-
ysis, only Kassin and Fong’s paradigm utilized stimuli that simulated an investigative
interview (Kassin & Fong, 1999). Other studies employed either (a) the classic de-
ceptive opinion/attitude paradigm (DePaulo & Pfeifer, 1986; Ekman et al., 1999),
(b) deceptive witnesses to an event (Chahal & Cassicy, 1995; Kohnken, 1987), or
(c) deceptive accounts of personal experiences (Porter et al., 2000). Although some
previous studies have developed more realistic, forensically relevant detection tasks,
these studies either did not include the necessary control condition (e.g., Vrij, 1993)
or failed to provide the statistics necessary to examine an investigator bias effect (e.g.,
Kraut & Poe, 1980). As noted earlier, our concern is that if investigators are truly
biased toward deception (or guilt) in their initial judgments, then preinterrogation
interviews could prompt the subsequent use of strong, pressure-filled methods of
interrogation that, in turn, could increase the risk of coerced false confessions.
To provide a true empirical test of the investigator bias hypothesis, we assessed
the deception-detection abilities of police investigators in the context of an inves-
tigative interview. In doing so, the present investigation extended recent work by
Kassin and Fong (1999), who experimentally trained some student participants, but
not others, in the detection of truth and deceit, before obtaining judgments of mock
suspects. Their study was unique in two ways. First, the authors administered the pop-
ular “Reid Technique, which has been employed in the training of tens of thousands
of law enforcement personnel. This training purports to enhance deception-detection
ability through the use of various verbal and nonverbal behavioral cues (see Inbau
Law and Human Behavior [lahu] pp614-lahu-450951 September 4, 2002 20:33 Style file version June 4th, 2002
474 Meissner and Kassin
et al., 2001). Second, these authors created a set of forensically relevant stimulus tapes
depicting brief interviews and denials of individuals who were either truly guilty or
innocent of committing one of four mock crimes.
Kassin and Fong (1999) showed the videotapes to trained and na¨ıve student
participants who attempted to detect whether the mock suspects were lying or truth-
ful. Their results indicated that although training did not increase overall detection
accuracy, it did increase the confidence that trained students had in their judgments
as well as the number of reasons they cited as a basis for their judgments. As shown
in Table 1, our reanalysis of the data also indicated that the training procedure trig-
gered a response bias toward guilt. From a practical standpoint, of course, these
data are importantly limited by the fact that the observers were college students, not
police detectives, and that the training manipulation was brief and condensed, not
offered in the context of professional specialization. As such, this study was designed
to extend this paradigm by testing experienced police investigators, some of whom
had received training in interviewing, interrogation, and the detection of deception.
Our objectives were twofold: (1) to compare the judgments of police investigators to
Kassin and Fong’s trained and na¨ıve college students (Kassin & Fong, 1999) and (2) to
examine—within our samples of investigators—the correlations between experience,
training, and various indices of performance.
Forty-four North American law enforcement investigators participated in the
study. Twenty-five investigators were affiliated with local police departments in
Florida, and 19 were from local departments in Ontario, Canada. No differences
were found in the experience or performance of the two samples. Investigators aver-
aged 13.7 years of law enforcement experience (SD = 6.5), and 68% had undergone
formal professional training in interviewing, interrogation, and the detection of the
Investigators were shown Kassin and Fong’s crime interview tapes, the details
of which are provided in their study (Kassin & Fong, 1999, pp. 501–504). Altogether,
eight guilty suspects committed one of four mock crimes (vandalism, shoplifting,
breaking and entering, a computer break-in), and eight innocent suspects were in-
structed merely to appear at the scenes of these crimes. All suspects were appre-
hended, taken to an interrogation room, and questioned by an adult male playing
the role of a detective. The interrogator, “Detective McCarthy,” was informed about
the mock crime that was committed but was blind to each suspect’s guilt or inno-
cence. The interviews, which were videotaped, ranged from 3.5 to 6.0 min in duration,
with a mean of 4 min 35 s. Self-reports of the participant suspects indicated that the
sessions were somewhat stress-provoking, and that the detective was intimidating in
his demeanor.
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Investigator Bias 475
Table 2. Deception-Detection Performance of Students and Police Investigators
Kassin & Fong (1999)
Na¨ıve students Trained students Police investigators
(N = 20) (N = 20) (N = 44)
Judgment accuracy 56% (15%) 46% (17%) 50% (19%)
Confidence 5.91 (0.78) 6.55 (1.02) 7.05 (0.96)
No. of reasons citd 2.98 (0.82) 3.96 (0.85) 2.14 (0.71)
Hits 56% (17%) 45% (17%) 62% (21%)
False alarms 42% (34%) 60% (38%) 67% (26%)
0.63 (0.23) 0.52 (0.24) 0.48 (0.28)
0.14 (0.72) 0.18 (0.80) 0.46 (0.55)
Note. Standard deviations are provided in parentheses.
In both samples, investigators were randomly assigned to view one of two video-
tapes, each depicting eight male suspects (four guilty and four innocent) repeat-
edly denying their involvement in the crime. After completing a brief background
questionnaire, investigators were instructed that they would view a tape of eight
male suspects, and that they were to decide whether each individual was lying or
truthful regarding his involvement. As in Kassin and Fong’s study, investigators were
told that between one fourth and three fourths of the suspects were lying to protect
In addition to making a truth/deception judgment regarding each sus-
pect, investigators rated their confidence on a scale from 1 (not at all confident)to
10 (extremely confident), and wrote in their own words the basis for their judgment.
Given that Kassin and Fong’s student participants completed the same task under
identical circumstances, their performance will be compared with that of our police
Table 2 presents the results for our police investigators as well as those of
Kassin and Fong’s na¨ıve and trained student participants who responded to the same
stimuli (Kassin & Fong, 1999). A one-way analysis of variance (ANOVA) was per-
formed on each performance variable for the three-way contrast of na¨ıve students
versus trained students versus police investigators. Planned comparisons then as-
sessed statistical differences in the performance of police investigators to that of the
student samples. The p <.05 convention for significance was employed across all
This range of deception was provided to capture variability in the response bias parameter, and is
a generally accepted detection task instruction. Any systematic fluctuations in response bias across
conditions resulting from such an instruction would demonstrate the influence of differential strategies
or preconceived base rates. Alternatively, overt specification of the 50% deception used in this study
would have suppressed the response bias parameter and hindered any such variation across conditions.
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476 Meissner and Kassin
Overall Judgment Accuracy, Confidence, and Reasons Cited
So that our results would be comparable with previous studies, we computed
judgment accuracy scores across all targets. As shown in previous studies, overall ac-
curacy (including both truthful and deceitful targets) for the investigators and student
participants did not significantly differ, F(2, 81) = 1.54, ns, η
= .03. However, a
significant effect on confidence was observed, F(2, 81) = 11.50, p <.001, η
= .22.
Planned comparisons revealed that both na¨ıve and trained students were significantly
less confident than police investigators, ts(62) = 4.87 and 2.16, ps <.001 and .05, re-
spectively. Interestingly, judgment accuracy and confidence were not significantly
correlated across investigators, r(43) = .20, ns, indicating poor calibration in detec-
tion performance. Participants were also asked to indicate their reasons for judging
the target as truthful versus deceitful. Results revealed a significant effect across
participant samples, F(2, 81) = 39.25, p <.001, η
= .49. Planned comparisons in-
dicated that both na¨ıve and trained students produced significantly more reasons
than did police investigators, ts(62) = 4.15 and 8.95, respectively, all ps <.001. Re-
sults of a comparative analysis of the combined sample of students versus police
investigators also replicated the above pattern.
Signal Detection Analysis
As described earlier, we separated performance into estimates of “hits” (the
proportion of deceitful suspects correctly identified as deceitful) and “false alarms”
(the proportion of truthful suspects incorrectly identified as deceitful). Analysis of hit
responses yielded a significant effect across participant samples, F(2, 81) = 5.38, p <
.01, η
= .12. Planned comparisons revealed that trained students produced signifi-
cantly fewer hits relative to the police investigators, t(62) = 3.18, p <.01; na¨ıve stu-
dents, however, did not significantly differ from the investigators, t(62) = 1.13, ns.A
significant main effect of participant sample was also observed with false alarm re-
sponses, F(2, 81) = 4.58, p <.01, η
= .10. Planned comparisons revealed that na¨ıve
students generated significantly fewer false alarms relative to police investigators,
t(62) = 3.25, p <.01, although the difference between trained students and investi-
gators was not significant, t(62) = 0.88, ns. When student samples were combined, re-
sults indicated that investigators generated significantly more hits, t(82) = 2.71, p <
.01, and more false alarms, t(82) = 2.00, p <.05.
When these estimates were used to compute measures of A
and B
, results
indicated a significant investigator bias effect, consistent with our studywise analy-
sis. Analysis of the discrimination accuracy parameter revealed no significant differ-
ences across participant samples, F(2, 81) = 2.11, ns, η
= .05. Yet a significant effect
of response bias was observed, F(2, 81) = 5.92, p <.01, η
= .13. Planned compar-
isons revealed that na¨ıve students significantly differed from police investigators,
t(62) = 3.68, p <.001. Although trained students demonstrated a more conserva-
tive response bias relative to police investigators, this difference failed to reach
conventional levels of significance, t(62) = 1.68, ns. A comparison of the combined
sample of students versus investigators also indicated no significant differences on
discrimination accuracy, t(82) = 1.61, ns, but an investigator bias effect in estimates
of response criterion, t(82) = 3.05, p <.01.
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Investigator Bias 477
Correlational Analyses
Comparison of law enforcement professionals to college students is one way
to gauge the role of experience and training on deception-detection performance.
Within our sample of investigators, we also examined the correlations between the
amount of training and experience the investigatorshad received and key measures of
task performance. First, prior experience (years) in law enforcement was not related
to either overall judgment accuracy, r(44) =−.19, decision confidence,r (44) =−.07,
or the number of reasonsinvestigators cited for their decisions, r(44) =−.03. In terms
of signal detection parameters of performance, however, greater prior experience
was significantly correlated with both an increase in false alarm responses, r(44) =
.33, p <.05, and an increased bias in responding “deceit,r(44) =−.34, p <.05. A
similar pattern emerged for the effect of deception-detection training with regard
to its lack of influence on both judgment accuracy and decision confidence, rs(44) =
.04 and .01, respectively. As might have been expected, however, prior training
did significantly increase the number of reasons that investigators cited for their
decisions, r(44) = .41, p <.01, and marginally prompted an increase in false alarm
responses, r(44) = .25, p <.10, and a bias to see deceit, r(44) =−.28, p <.10.
While detecting deception seems an inherently difficult task, the judgments that
police investigators make of suspects on the basis of preinterrogation interviews
represent a critical choice point in law enforcement, as they determine whether
suspects are sent home or subjected to guilt-presumptive interrogation. Given the
importance of this decision-making process, deception-detection techniques that rely
on an analysis of verbal and nonverbal behavioral cues have been used as a basis
for training. Despite the assumption that such programs enhance accuracy, however,
published psychological research has generally failed to demonstrate performance
increments as a function of special training or prior law enforcement experience
(Bull, 1989; DePaulo & Pfeifer, 1986).
Our goal was to better understand the influence of training and experience on
deception-detection judgments. Unfortunately, previous studies had focused upon
global accuracy rates rather than separating performance for both truthful and deceit-
ful targets. By separating these two aspects of performance, the application of SDT
affords the opportunity to distinguish between two conceptually and computation-
ally independent parameters of detection skill: discrimination accuracy—correctly
detecting a signal (deception) versus correctly rejecting its absence (truth), and
response bias—the threshold of evidence necessary for an individual to respond
that a signal (deception) has been presented. On the basis of the assumptions under-
lying manipulations of training or experience, one would expect that discrimination
accuracy would be enhanced; however, given the relative independence of the two
parameters, response bias should not be influenced by such manipulations.
To test this hypothesis, we first conducted a studywise analysis of the previous
literature in which estimates of discrimination accuracy and response bias were cal-
culated. Effect sizes were computed for each study, after which they were weighted
Law and Human Behavior [lahu] pp614-lahu-450951 September 4, 2002 20:33 Style file version June 4th, 2002
478 Meissner and Kassin
by sample size and aggregated across studies for each SDT parameter. The results of
this analysis indicated a reliable effect on estimates of response bias. In particular,
training and experience appeared to loosen participants’ response criterion, thereby
increasing the likelihood that they would judge targets as deceitful rather than truth-
ful relative to a no-training or experience control group. Across studies, however,
training and experience produced no reliable effects on the ability to discriminate
between truth and deceit.
To more directly assess the validity of this “investigator bias effect” in a foren-
sically relevant setting, we presented a sample of law enforcement investigators
with videotapes of brief interviews in which guilty or innocent male suspects de-
nied their involvement in a mock crime. The task was to determine whether each
suspect was truthful in his denial or lying to cover his guilty actions. We compared
the performance of our police investigators with that of na¨ıve and trained student
participants from the study of Kassin and Fong (1999), who completed the task
with the same stimuli and under identical conditions. Overall, the investigators did
not outperform Kassin and Fong’s trained or na¨ıve student participants (Kassin
& Fong, 1999), in terms of either global accuracy or discrimination performance
). However, they were significantly more confident in their judgments and sig-
nificantly more likely to respond “deceitful” rather than “truthful”—a liberal re-
sponse bias that is consistent with our reanalysis of the literature. In short, the piv-
otal decision investigators must make regarding whether to further interrogate a
suspect may be based on prejudgments of guilt, confidently made, but frequently in
One might argue that our investigators were limited in their performance by
the relative brevity and low-stakes nature of the taped interviews. As noted earlier,
however, their accuracy rate is consistent with past studies of law enforcement pro-
fessionals. Moreover, this possible limitation with regard to the targets of judgment
used in this study cannot explain the response bias or high confidence levels exhib-
ited by investigators relative to students (indeed, from a metacognitive perspective,
one would hope that professionals would adjust their confidence levels according
to such perceived limitations). One might also argue that investigators were limited
by their ability to merely observe, not actively conduct, the interviews. Importantly,
however, research in other contexts has shown that judgments of truth and decep-
tion are more accurate when made by observers than by conversational interactants
(Buller, Strzyzewski, & Hunsaker, 1991).
Given the potential and serious consequences of an investigator bias effect, it
will be important in future studies to consider both the theoretical mechanisms and
practical implications of the observed bias. From a theoretical perspective, social
cognitive mechanisms may be responsible for the investigator bias due to experi-
ence or training. For example, investigators in a deception-detection task may be
influenced by subjective probabilities, or base rates, for the incidence of truth versus
deceit (Fiedler, 2000), and these probabilities may be influenced by factors, such as
the race, age, ethnicity, criminality, or status of the suspect (Ruby & Brigham, 1996),
or by the contextual basis of the interview itself (e.g., whether there is indepen-
dent, corroborative evidence). These initial attributions may then set the stage for
other mechanisms, including the manner in which investigators encode and process
Law and Human Behavior [lahu] pp614-lahu-450951 September 4, 2002 20:33 Style file version June 4th, 2002
Investigator Bias 479
seemingly relevant information (Kassin et al., 2001; Nickerson, 1998). For example,
police investigators may encode and weight information that has little discriminative
validity (see Simon, 1991). Although such mechanisms were not tested in this study,
future research should consider their influence in the investigator bias effect and
seek to dissociate the effects of training and prior experience.
From a practical standpoint, the investigator bias uncovered in this study sug-
gests that many innocent suspects are in a precarious situation before undergoing
formal interrogation. Routinely, investigators seek to assess a suspect’s veracity in
order to determine whether to launch into an interrogation, a process that, at times,
elicits coerced false confessions from innocent people. Another possible detrimen-
tal effect on the innocent suspect may arise from the influence of trial testimony
provided by investigative officers on the perceived truthfulness of the defendant.
Although this proposition remains to be empirically tested, it is possible that such
confident and descriptive testimony—accurate or not, and biased or not—may have
a strong effect on jurors and jury decision-making. Thus, in light of the profound risks
to the accused, both in the interrogation room and subsequently in the courtroom,
we believe that further research is warranted regarding the theoretical mechanisms
responsible for the effect and the practical ramifications on the disposition of a given
The authors thank John Turtle for assisting with data collection.
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... BAI interviewers rely on methods of detecting truth-and lie-telling behaviors to determine if a formal interrogation of the suspect is necessary; those judged as deceitful are moved into an accusatory interrogation phase where the goal is to obtain a confession (Inbau et al., 2013). The basis of this initial judgment of deceit in the interview is a crucial step in the investigative process, as any error lays the groundwork for an innocent individual to be subjected to further accusatory and coercive interrogation tactics that could lead to a false confession (Gould & Leo, 2010;Meissner & Kassin, 2002; see also Scherr et al., 2020). This is especially true for juveniles, who are uniquely vulnerable to the pressures put on them by police officers, more susceptible to commonly used interrogation techniques, and more likely to falsely confess than adults (e.g., Cleary, 2017;Redlich & Goodman, 2003). ...
... Proponents of the Reid Technique claim that interviewers trained in the BAI can distinguish between truthfulness and deceitfulness 85% of the time (Inbau et al., 2013), yet extensive research shows that individuals typically cannot detect deception at better than chance rates (Bond & DePaulo, 2006). Moreover, BAI training does not typically improve lie detection skills; officers trained in the Reid Technique show increased confidence in their judgments of deception, but no increase in the accuracy of their judgments (Meissner & Kassin, 2002). While limited research has investigated police officers' ability to detect deceit in juveniles, Vrij, Akehurst, and Knight (2006a) found police officers, social workers, teachers, and laypersons believed children, adolescents, and adults typically exhibit the same cues to deception (e.g., nervousness, gaze aversion, and evasive responses). ...
... On the other hand, innocent suspects may not actively manipulate their behaviors because they have an overwhelming belief that their innocence will easily be seen by interrogators (Kassin, 2005). Consequently, more innocent suspects may be mistakenly judged as deceitful by police, as officers have been shown to have a bias towards judging suspects as guilty (e.g., Kassin, 2005;Meissner & Kassin, 2002;Narchet et al., 2011). ...
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Police officers are often trained to use the Behavior Analysis Interview (BAI) to detect deceit, but it is based on faulty indicators of lying that may be especially problematic for juveniles due to developmental immaturities. Juveniles, young adults, and adults were assigned to guilt or innocence conditions, read a criminal scenario, and self‐reported their likelihood of providing truthful and deceitful responses during a hypothetical BAI. All participants indicated they would give more truthful than deceptive responses. Guilty participants reported more use of strategies to appear innocent, while innocent participants said they would behave naturally. Juveniles were more likely to choose deceitful responses and say they would use strategies to appear innocent during a police interview but endorsed fewer stereotypical cues of deception compared to adults. Juveniles may not recognize how certain behaviors could be seen as cues to deception, which could put them at risk of being misidentified as guilty. This article is protected by copyright. All rights reserved.
... Опасность мифа о «живом детекторе лжи» не только в том, что полицейские ошибочно классифицируют невиновных как виновных на основании самого ненадежного критерия [107], но также в том, что он существенно повышает веру полицейских в правильность их ошибочных суждений [100,101,108,109]. Неадекватная уверенность в своих ошибочных суждениях -это большая проблема в работе следователя, так как цена ошибки очень высока -страдают свобода и репутация невиновного человека, а виновный избегает наказания и получает возможность снова совершить преступление. ...
... Неадекватная уверенность в своих ошибочных суждениях -это большая проблема в работе следователя, так как цена ошибки очень высока -страдают свобода и репутация невиновного человека, а виновный избегает наказания и получает возможность снова совершить преступление. Ошибочные суждения по поводу обмана со стороны подозреваемого приводят к эффекту, который Meissner и Kassin [108,109] назвали предубежденной реакцией следователя (т. е. склонность предполагать вину подозреваемого с полной или почти полной уверенностью). ...
... 3 Переводные статьи / Translated Articles вного подозреваемого за виновного, не позволяет ему расследовать новые или имеющиеся зацепки, улики, теории, указывающие на других возможных подозреваемых. Как было показано в работах Kassin и других, ошибочные, но чрезмерно уверенные суждения по поводу обмана со стороны подозреваемого также повышают вероятность того, что невиновный подозреваемый будет подвергнут обвинительному допросу, в ходе которого следователи стараются получить информацию, подтверждающую их предварительные выводы о виновности, и отвергают улики, противоречащие этой версии [110,111,108,109]. ...
Objective : to summarize and study the law-application errors during preliminary interrogation, court investigation, and conviction in the American criminal justice system. Methods : dialectical approach to cognition of social phenomena, allowing to analyze them in historical development and functioning in the context of the totality of objective and subjective factors, which predetermined the following research methods: formal-logical and sociological. Results : the work describes in detail and considers four main causes of law-application errors occurring during preliminary interrogation, court investigation, and conviction in the American criminal justice system. These include: false confessions, eyewitness misidentification, forensic error, and perjured jailhouse informant testimony. Hence, it is not accidental that the main task of empirical research of criminologists and other researchers in the past two decades has been a call for greater transparency in the evidence-gathering process and the development and implementation of best practices based on social science research. Developing conceptual knowledge is important not only for creating a more systematic, generalizable and respectable criminology of wrongful conviction, but also to better inform policy-makers’ understandings that people’s lives may be at stake, as well as trade-offs of wrongful convictions. Scientific novelty : the work considers the current problems in the American criminal justice system, that occur during preliminary interrogation, court investigation, and conviction. Among them are the problems of police interrogations, false confessions and court errors, leading to wrongful convictions. Practical significance : the main provisions and conclusions of the article can be used in scientific, pedagogical and law enforcement activities when considering the issues related to the minimization of errors occurring at the stages of preliminary interrogation, court investigation, and conviction in the American criminal justice system. The article was first published in English language by Criminology, Criminal Justice, Law & Society and The Western Society of Criminology Hosting by Scholastica. For more information please contact: . For original publication: Leo, R. A. (2014). The Justice Gap and the Promise of Criminological Research, Criminology, Criminal Justice, Law & Society, 15 (3), 1–37. Publication URL:
... Meissner has evaluated the deception detection and interviewing/interrogation literatures, including conducting several metaanalyses in this area (Meissner & Kassin, 2002;Meissner et al., 2017;Snook et al., 2021). He has also co-organized a conference sponsored by the American Psychological Association on investigative interviewing. ...
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This is the protocol for a Campbell systematic review. The objective is to assess the effects of interrogation approach on confession outcomes for criminal (mock) suspects.
... Base-rate assumptions might be influenced by the "deception consensus effect" (e.g., Markowitz, 2022;Markowitz & Hancock, 2018; see also Sagarin et al., 1998); that is, individuals who lie often also expect others to lie frequently. Moreover, base-rate assumptions also show in the "investigator bias" (Meissner & Kassin, 2002); individuals experienced in lie detection (e.g., police officers) are confronted with lies more often than naive individuals. A higher generalized suspicion of these experienced individuals (see, e.g., Masip et al., 2005) is assumed to result in a higher tendency to classify messages as lies (e.g., Bond & DePaulo, 2006;Garrido et al., 2004). ...
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Research suggests that people differ more in their ability to lie than in their ability to detect lies. However, because studies have not treated senders and messages as separate entities, it is unclear whether some senders are generally more transparent than others or whether individual messages differ in their transparency of veracity regardless of senders. Variance attributable to judges, senders, and messages was estimated simultaneously using multiple messages from each sender (totaling more than 45,000 judgments). The claim that the accuracy of a veracity judgment depends on the sender was not supported. Messages differed in their detectability (21% explained variance), but senders did not. Message veracity accounted for most message variation (16.8% of the total variance), but other idiosyncratic message characteristics also contributed significantly. Consistent with the notion that a (mis)match between sender demeanor and veracity determines accuracy, lie and truth detectability differed individually within senders. Judges primarily determined variance in lie-versus-truth classifications (12%) and in confidence (46%) but played no role regarding judgment accuracy (< 0.01%). This work has substantial implications for the design and direction of future research and underscores the importance of separating senders and messages when developing theories and testing derived hypotheses.
... the base-rate expectations (the predicted probability) of human error for events in these two populations. However, research that directly demonstrated the effects of biased base-rates on professional investigative judgment is scarce (see Meissner & Kassin, 2002). The goal of the current research is to examine the magnitude of the human error bias in professional investigation and provide concise, empirical evidence of the biasing effect of base-rates on professional judgments. ...
Introduction: This study explored the magnitude of professional industrial investigators' bias to attribute cause to a person more readily than to situational factors (i.e., human error bias). Such biased opinions may relieve companies from responsibilities and liability, as well as compromise efficacy of suggested preventative measures. Method: Professional investigators and undergraduate participants were given a summary of a workplace event and asked to allocate cause to the factors they found causal for the event. The summary was crafted to be objectively balanced in its implication of cause equally between two factors: a worker and a tire. Participants then rated their confidence and the objectivity of their judgment. We then conducted an effect size analysis, which supplemented the findings from our experiment with two previously published research studies that used the same event summary. Results: Professionals exhibited a human error bias, but nevertheless believed that they were objective and confident in their conclusions. The lay control group also showed this human error bias. These data, along with previous research data, revealed that, given the equivalent investigative circumstances, this bias was significantly larger with the professional investigators, with an effect size of dunb = 0.97, than the control group with an effect size of only dunb = 0.32. Conclusions: The direction and strength of the human error bias can be quantified, and is shown to be larger in professional investigators compared to lay people. Practical applications: Understanding the strength and direction of bias is a crucial step in mitigating the effects of the bias. The results of the current research demonstrate that mitigation strategies such as proper investigator training, a strong investigation culture, and standardized techniques, are potentially promising interventions to mitigate human error bias.
... For example, some studies suggest that experienced police officers may selectively recall their professional experiences, leading them to be overly confident about a suspect's guilt (Areh et al., 2016). Similarly, they also might overestimate their ability to detect lies (Leo, 1996), which research has shown is not much better than that of lay people (Bond & DePaulo, 2006;Meissner & Kassin, 2002). In fact, studies suggest that even a little experience can lead to overconfidence among beginners who are trying to master a specific task (Sanchez & Dunning, 2018). ...
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This exploratory study is intended to serve as a gateway to future research about the differences between sexual murderers with (HSAO) and without (N-HSAO) a recorded criminal history of sexual assault, on which there is little to no comparative literature. This study aims to extend our understanding of these groups by comparing their crime scene (and crime-related) behaviors and exploring their underlying psychological functioning. The results suggest that N-HSAO have a significantly higher tendency to murder friends or strangers, initially attack or abduct their victims from the victim’s residence, use more than one killing method in the murder, attack their victims in the context of allegedly consensual sex, and insert themselves to the investigation. Other behavioral trends suggest differences between the groups in criminal savviness, risk-taking, emotional reactions, sexual behaviors and preferences, and differences in the behavior of serial and non-serial offenders. Implications for our understanding of the underlying psychological makeup of these offenders, guidelines for criminal investigations, and directions for future research are discussed.
... Police detectives also come to more guilty judgements than students (Culhane & Hosch, 2012), which can be explained by their distrust of suspects in general (e.g. Kassin et al., 2003;Meissner & Kassin, 2002;Vrij, 2008) and of their alibis in particular (Dysart & Strange, 2012). When a suspect changes his alibi, for example, about 80% of the police detectives think that the change is made due to deception rather than error (Dysart & Strange, 2012), although such misrecollections are common occurrences (Crozier et al., 2017;Strange et al., 2014). ...
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Until now, supportive evidence for alibis has been conceptualised into two distinct types: witness and physical evidence. The present study examined whether knowledge, as a third type of supportive evidence, can contribute to the understanding of evidence for alibis. Three experiments were conducted in which police detectives, laypersons and undergraduate students were asked to evaluate four alibis with witness, physical or knowledge supportive evidence, or with no supportive evidence. The results from the three experiments show that knowledge evidence is equally believable as strong witness evidence. We also found that not all items of strong physical evidence are evaluated as equally strong and believable. We therefore suggest adjusting the criteria to determine the strength of physical evidence and conducting more research on knowledge evidence.
Tunnel vision is the tendency of actors in the criminal justice system to use short-cuts to filter evidence selectively to build a case for a suspect’s conviction. Confirmation bias tends to favor information that confirms an individual’s preconceptions independently of the information’s accuracy: the present study manipulated tunnel vision and confirmation bias. The purpose was to examine the combined effects of these biases on Israeli police investigators and laypeople in hypothetical criminal investigation situations. Results indicated that police investigators were more strongly affected than laypersons by tunnel vision. Police investigators were more confident about the suspect’s guilt than were laypeople in the presence of incriminating and exonerating information, alike. Still, investigators did not ignore exonerating information and lowered their confidence in the suspect’s guilt when exonerating information was presented. We discussed the results according to police legitimacy and self-assessed lie-detection ability, which is rated higher by police investigators than by laypeople.
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This research investigates whether police officers can reliably use behavioral cues to determine whether a person is conceal- ing an object. Using a Lens Model framework, we performed a mega-analysis of three experiments. In each study, officers and laypersons judged whether people were concealing an object and reported “articulable behaviors” they used to perform this task. Although participants were able to articulate behaviors that they believed were helpful, results showed that these behaviors were not related to whether the person was actually concealing. Officers and laypersons were equally poor at judging whether someone was concealing or not. Current officer training on the use of nonverbal behaviors to determine who is concealing a dangerous object may be ineffective, and a reconsideration of training is warranted. In light of the findings, requiring officers to provide “articulable behaviors” in Fourth Amendment cases may not provide a sufficient safeguard against unreasonable searches of civilians.
We are constantly forming impressions about those around us. Social interaction depends on our understanding of interpersonal behavior - assessing one another's personality, emotions, thoughts and feelings, attitudes, deceptiveness, group memberships, and other personal characteristics through facial expressions, body language, voice and spoken language. But how accurate are our impressions and when does such accuracy matter? How is accuracy achieved and are some of us more successful at achieving it than others? This comprehensive overview presents cutting-edge research on this fast-expanding field and will be essential reading for anyone interested in the psychology of interpersonal perception. A wide range of experts in the field explore topics including age and gender effects, psychopathology, culture and ethnicity, workplaces and leadership, clinicians' skills, empathy, meta-perception, and training people to be more accurate in their perceptions of others.
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Confirmation bias, as the term is typically used in the psychological literature, connotes the seeking or interpreting of evidence in ways that are partial to existing beliefs, expectations, or a hypothesis in hand. The author reviews evidence of such a bias in a variety of guises and gives examples of its operation in several practical contexts. Possible explanations are considered, and the question of its utility or disutility is discussed. When men wish to construct or support a theory, how they torture facts into their service! (Mackay, 1852/ 1932, p. 552) Confirmation bias is perhaps the best known and most widely accepted notion of inferential error to come out of the literature on human reasoning. (Evans, 1989, p. 41) If one were to attempt to identify a single problematic aspect of human reasoning that deserves attention above all others, the confirma- tion bias would have to be among the candidates for consideration. Many have written about this bias, and it appears to be sufficiently strong and pervasive that one is led to wonder whether the bias, by itself, might account for a significant fraction of the disputes, altercations, and misun- derstandings that occur among individuals, groups, and nations.
Examined the physical cues that people use in social judgments and the generality of their use across perceivers. 34 male and 5 female professional inspectors in the US Customs Service and 29 female and 20 male nonstudent adult laymen judged whether they wanted to search airline passengers going through a mock customs inspection. An analysis of travelers' demographic characteristics and verbal and nonverbal behaviors showed that Ss' decisions to search travelers were based primarily on the travelers' comportment. Comportment mediated the effects of demographic characteristics and had direct effects on decisions. 21 variables accounted for 72% of the variance in search decisions, and 6 variables accounted for 60% of the variance. Bivariate analyses showed the travelers were most likely to be searched if they were young and lower class, appeared nervous, hesitated before answering, gave short answers, avoided eye contact with the interviewer, shifted their posture, and had taken pleasure trips. Individual differences among Ss--inspectors vs laymen, successful vs less successful inspectors, and high vs low self-monitors--had little effect on the cues they used. Results demonstrate the value of a social psychophysical approach to person perception that focuses on the behavior of the perceived. (55 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved).
It was predicted that trained observers would detect deception more accurately than untrained observers. More specifically, it was predicted that the highest deception detection accuracy would be found among trained observers judging the veracity of low self-monitors and unrehearsed liars, whereas the lowest detection accuracy would be found among untrained observers judging the veracity of high self-monitors and rehearsed deceivers. It also was hypothesized that the discrepancy between observers‘actual ability to detect deception and their certainty in the accuracy of their judgments would be smaller for trained observers than for untrained observers. Observers trained to detect deception used six behavioral cues based on research by deTurck and Miller (1985): (a) message duration, (b) response latency, (c) adaptors, (d) pauses, (e) nonfluencies, and (f) hand gestures. Results confirmed both hypotheses.
This experiment compared the deception detection skills of conversational participants and observers. Participants were expected to have a more pronounced truth‐bias than observers. They were also predicted to be less accurate detecting deception than observers because of the cognitive and communication requirements of conversational management. Each of fifty observers viewed two videotaped interactions between an interviewer (i.e., conversational participant) and two interviewees (i.e., sources) who either told the truth or deceived. Conversational participants attributed more truth to sources than did observers and they were less accurate detectors than observers. When not told about the deception manipulation, observers relied on more accurate behavioral cues than participants. When informed about deception, participants relied on inaccurate facial cues, whereas observers relied on inaccurate vocal cues to judge deceit.
The role of on-the-job experience in fostering skill at detecting deception was examined. A deception-detection test was administered to three samples of more than 100 subjects each: a group of undergraduates with no special experiences at detecting deceit; a group of new recruits to a federal law enforcement training program, who had some limited on-the-job experience at detecting deceit; and a group of advanced federal law enforcement officers, with years of experience working at jobs in which the detection of deception is very important. Although the officer samples were more confident about their judgments of deceptiveness than were the students, they were no more accurate than the students. None of the three groups showed a significant improvement in deception-detection success from the first half to the second half of the test; however, the advanced officers felt increasingly confident about their performance as they progressed through the test. Correlational analyses of the relationship between accuracy and confidence provided further evidence that experience does not improve people's awareness oi the accuracy or inaccuracy of their judgments. The findings from this research are compared to the results of research on other kinds of professional decision-makers (e.g., clinical psychologists), and several theoretical perspectives on the role of experience in decision making are discussed.
All deception studies published to date have been laboratory studies. In such studies people lied only for the sake of the experiment, consequently the stakes were usually low. Although research has shown that most spontaneous lies told in real life are trivial, such studies tell us little about lies where the stakes are high (such as police/suspect interviews). In Study 1, we discuss the behaviour of an actual suspect while he was interviewed by the police in a murder case. Although the man initially denied knowing and killing the victim, substantial evidence obtained by the police showed that he was lying. On the basis of this evidence, the man confessed to killing the victim and was later convicted for murder. To our knowledge there has been no other study published that has analysed the behaviour of a liar in such a high-stake realistic setting. The analysis revealed several cues to deception. In Study 2, we exposed 65 police officers to six fragments (three truthful and three deceptive) of the interview with the murderer and asked them to indicate after each fragment whether the man was lying or not. The findings revealed that the participants were better at detecting truths (70% accuracy) than lies (57% accuracy). We also found individual differences among observers, with those holding popular stereotypical views on deceptive behaviour, such as ‘liars look away’ and ‘liars fidget’ performing least effectively as lie catchers. Copyright © 2001 John Wiley & Sons, Ltd.