How to become a human lie detector – understanding the science of deception

"Never attempt to win by force, that which can be won by deception" (Machiavelli)

Over the years I've spent in the courtroom and the boardroom, I'd like to think I have a pretty good idea if someone is lying to me. I have interviewed hundreds of witnesses and thousands of clients.?

In my experience, you can get close to the truth by forensically analysing someone’s story against the available evidence.?That’s what lawyers do.

However, when there is no direct evidence available, you are usually left with a gut feeling about whether someone is telling the truth - the sense that something wasn’t right with their story or behaviour.??While a gut feeling has its place, it is possible to pick a liar much more accurately and reliably.??The answer is in the science.

Baseline Behaviour

Human beings are actually very bad liars.??Believe it or not, most people don’t want to lie and send very strong signals when they do - signals you can learn to identify and read.?

The first step to separating the truth from the lie is to identify a baseline of behaviour and language.?How does the person behave when they are comfortable and truthful???Are they fidgety and vague or calm and precise??

Once you have a baseline you need to formulate the right questions and listen very carefully to the answers.

Specific Questions

The questions need to directly and specifically address the relevant allegation.??Don’t imply a question or make the question too long to follow.?Ask short, direct questions - “did you read this email on Monday?” is much better than “you would have understood the emails sent to you wouldn’t you?”.?The second question gives too much latitude to deceive without directly lying.?

Avoiding a Lie

The next step is the most important - listen carefully to all the person’s answers, including what happened before and after the part you are interested in.?

People will work very hard to avoid telling a lie if they can.?They will just skip over that part if the interviewer allows it. Or they will address a different question about the same issue to avoid lying, like Lee Harvey Oswald’s public statement:

Question: “did you kill the president?”

Answer: “I have not been charged with that”

Pretty damning.?

If they are clever, they might give an answer that addresses the question that is technically true but is intended to deceive.?The most famous example is President Clinton’s statement:

“I did not have sexual relations with that woman, Ms Lewinsky”

This statement is hardly a statement of full and frank honesty.

To avoid telling a direct lie, witnesses will often:

1.?????Not answer the question

2.?????Leave out the critical fact

3.?????Pretend to forget

4.?????Pretend they don’t know

All of the above are indicative of deception when compared to the person's baseline or the rest of their evidence.?

Lying Language

The numbers also show that people use different language when they are telling a lie.?

Specific statements made in the “first person active past tense” ("I walked the dog on Saturday") are indicative of truth, while more vague statements in the passive tense ("the dog would have been walked by me on Saturday") are indicative of deception.?

You might think that nobody would be that vague but I’ve seen it happen.?In fact, I’ve seen witnesses use very clear, specific, active, first-person language for part of their evidence, then suddenly switch to more passive and vague language for the part that is not true, then switch back again when they return to the truth.?It is amazing to watch.

You Never Lie Twice

Another shocking truth is that people will avoid lying about their previous lie.??

Let me clarify – they can lie on multiple occasions in one statement, no problem, but they struggle to lie on two different levels about the same issue.?

You can catch them out by asking them about the relevant factual conduct, listening to the answer, then asking about the truthfulness of their statement.??The first question is about a state of fact and the second is about their truthfulness on the statement of fact.??

Generally deceptive witnesses will struggle to give a clear lie twice.?For example:

Question: Did you take the money?

Answer: No

Follow up Question: Should I believe you?

Generally, a truthful witness will answer the second question with “yes of course” or something similar, but a deceptive witness will give a vague answer like “I guess so” or even an accurate answer like, “that is up to you”.?

Something about the different levels of logic makes it very difficult for deceivers to directly lie twice about the same issue.?Truthful witnesses don’t have that problem.

Hidden Details

Even the smallest detail, like the time they spend on an answer, is telling.?The statistics show that around 85% of deceptive witnesses spend more time on the truthful parts of their stories than the lies.???

People don’t like to lie.?

The lie is likely to be the quick, vague, passive part of the statement in comparison to the baseline for that witness.

If that is not enough, people also give unconscious cues in their language.?They give you information they don’t want you to have.?They can’t help it.?For example, if a witness says:

“I had lunch with someone”

“I had lunch with a friend”

“I had lunch with a girlfriend”

“I had lunch with my girlfriend”?

Each of these statements indicate very different levels of closeness and trust between the people at the lunch.?This becomes more interesting when they answer questions that were not asked but they feel guilty about.

For example, when asked what he did on the evening of the shooting of his girlfriend, Oscar Pistorius, answered “Reeva would have gone out with her friends (a lie)… but we were content to have a quite dinner together at home” (another lie).?He starts vague about what she “would have done” then goes on to answer a question that was not asked – "were you both happy about staying home that night?”

The clear indication is that they were not happy about being at home that night.

The couple were probably fighting about her going out with her friends.?A clue to jealousy being the motive for the shooting.?People tell you exactly what they don’t want you to know.?They almost want to tell you because of the unconscious guilt of lying. That guilt even applies to people who appear to have very poor ethics.

Non-Verbal Clues

The final category of clues to deception are nonverbal.?

Some are physiological, like blood pressure and saliva, and some are behavioural, like eye movement, body language and micro expressions.?Again, having a baseline for the person when the are relaxed and truthful is critical.?

Eye movement, cheek redness, mouth dryness, body language etc. which is consistent with the witness’ usual level is indicative of truth while changes in the pattern is indicative of deception.?

Usually, extraverted people with good people skills look you in the eye when they lie, while introverts look away.?So, whether they look you in the eye on its own tells you nothing, but compared to the persons usual baseline behaviour, it tells you a lot.?

They key is to watch the witness and listen carefully to what they say.?Record it all if you can and watch it back.?Have their words transcribed and read them carefully.?The answers you seek might be right under your nose.