Why Criminals Lie – And Why Detectives Don't Just Listen to the Words
- Ken Kirwan
- 2 days ago
- 4 min read
One of the questions I am asked more than almost any other is:
"Can you tell when someone is lying?"
It's an understandable question. Television dramas would have us believe that experienced detectives can spot a liar because they avoid eye contact, fidget in their seat or suddenly become nervous. It makes for good television. The reality is very different.
After more than 30 years as a detective, I learned that successful investigations are rarely about reading body language. They are about understanding people, testing accounts and following the evidence wherever it leads. Interestingly, that is exactly where modern deception research has arrived.
Why do criminals lie?
People lie for many reasons. Some lie to avoid arrest or conviction. Others lie to protect family members, criminal associates or their own reputation. Sometimes people lie because they are ashamed of the truth. Occasionally, habitual offenders lie because deception has become a normal way of navigating life.
In my experience, the vast majority of offenders don't invent an entirely fictional story. Instead, they build a version of events around fragments of truth. They know that a story containing genuine details is often more believable than one that is completely fabricated.
Research into deception supports this observation. Studies suggest that liars often mix truthful information with falsehoods because it is cognitively easier to maintain and makes their account appear more plausible.
The biggest myth: body language
We've all heard the myths.
"If they won't look you in the eye, they're lying."
"If they cross their arms, they're hiding something."
"If they fidget, they're guilty."
Unfortunately, none of these beliefs stand up particularly well to scientific scrutiny. Professor Aldert Vrij, one of the world's leading researchers into deception at the University of Portsmouth, has spent decades examining how people detect lies. His conclusion is refreshingly simple: there is no single behavioural cue that reliably tells us someone is lying. Nervousness, looking away or fidgeting are just as likely to be displayed by truthful people who are frightened, embarrassed or sitting in a police interview for the first time.
That mirrors my own experience. Some of the most convincing liars I interviewed remained calm throughout. Equally, completely innocent people sometimes appeared highly anxious because they suddenly found themselves under enormous pressure.
So what are detectives looking for?
Good investigators are far less interested in isolated behaviours than they are in evidence.
Does the account fit with CCTV?
Is it supported by forensic evidence?
What do the mobile phone records show?
Do witness accounts support or contradict what has been said?
Can the explanation actually be tested?
Modern investigative interviewing has increasingly shifted away from trying to identify deception through behaviour and towards carefully analysing what people say and whether their account can be independently verified. Researchers now argue that verbal cues and the quality of an account are far more informative than body language alone.
Consistency isn't quite what people think
Many people assume that an honest witness will tell exactly the same story every single time. Human memory doesn't work like that.
Truthful people often remember different details on different occasions. They may recall something new when prompted or forget something insignificant the first time around. That is perfectly normal. What investigators are interested in is whether the core account remains credible and whether any changes make sense in light of everything else that is known.
By contrast, someone who has constructed a false narrative often has to keep modifying it as new evidence emerges. Each alteration creates fresh opportunities to test the account. That's why detectives become interested in chronology, detail and explanation—not because someone scratched their nose halfway through an interview.
Interviews are conversations—not interrogations
Popular culture loves the image of detectives aggressively confronting suspects until they confess. Thankfully, policing has moved on. Today's investigative interviews are built around planning, preparation and allowing people to provide their account in their own words. Good interviewers ask open questions, encourage detailed recall and carefully explore areas that can later be verified.
Research has increasingly shown that interview techniques which encourage suspects to provide richer, more detailed accounts often create opportunities for investigators to identify inconsistencies or information that can be independently checked.
Sometimes silence is one of the most powerful tools an investigator possesses.
People often continue talking simply because they become uncomfortable with silence. Frequently, the most revealing information comes after they believe they have already answered the question.
Evidence will always beat instinct
One lesson stayed with me throughout my policing career. Good detectives don't try to prove somebody is lying. They try to establish what actually happened. That means testing every account—whether from a suspect, witness or victim—against the available evidence.
Instinct has its place. Experience helps you ask better questions. But neither instinct nor body language secures convictions. Evidence does.
So, the next time you watch a detective drama where someone is declared guilty because they looked away or folded their arms, remember this: real investigations are usually quieter, slower and far more methodical.
The best detectives don't simply read people. They listen carefully, remain professionally curious and relentlessly test every account against the facts. Because in the end, evidence has a habit of outlasting even the most convincing lie.
Ken Kirwan is a former Detective Inspector with over 30 years' policing experience and is now a Lecturer in Policing and Criminology.
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