How Liars Tell the Truth

Apr 8, 2019

Nico Declercq

Nico Declercq at FraudTalks
Nico Declercq at FraudTalks
Nico Declercq at FraudTalks

Nico Declercq is a criminal investigator experienced in interviewing subjects. As an expert in body language and lie signal detection, to him an investigation ultimately comes down to truth detection, not lie detection.

As a crime investigator, I conduct investigations that are often about heavily charged, emotional events. For example, a fire that has burned down a house, a serious accident at work, or losses worth millions of dollars. In all these cases, I like to go to the scene and talk to the people involved. I don’t do it by phone, I don’t do it by email. I have to face people when I’m asking them questions. As Nietzsche already said in the nineteenth century: people lie with their mouths, but with their facial expressions they tell the truth. I have three different types of clues that help me tell a truthful story from a lie:

  • Non-verbal clues

  • Paraverbal clues

  • Verbal clues

Non-verbal clues are about body language and facial expressions. The way people speak is known as paraverbal communication. The verbal clues are in the words, the actual story that people tell me. As an investigator I have to observe everything and listen carefully in order to get to the truth.

How our bodies betray us

A liar can prepare a story and try to deceive me with verbal language. But body language is a law unto itself. There are several tell-tale signs that a person may be lying - or telling the truth. This doesn’t work the way it’s often portrayed in television series such as Lie To Me, where an expert will watch the video of an interview and say: “Freeze the frame, he’s lying.” I approach an interview according to the COI principle: Calibrate, Observe, Investigate. During the calibration phase, I ask the interview subject a few questions that I already know the answer to, such as their name. This way I can establish their regular facial expressions, body language, and speech pattern. There are several non-verbal criteria, such as micro-expressions (very brief and small facial expressions), changes in eye contact, and eye movements.

For instance, when you ask someone how many doors there are in their house, you will often see them looking at the upper right. They don’t do that because they expect the answer will magically appear on the ceiling, but because the recall memory is located on the right side of the brain. This doesn’t mean you can go home and ask your spouse: “Did you ever cheat on me?” and then tell they’re lying based on which direction they’re looking in. It’s just one small sign of what could be deception. I look out for non-verbal criteria and when I observe something that indicates the subject might be lying, then I will begin to ask a lot of questions.


How our speech betrays us

Besides non-verbal communication, it is important to pay attention to the paraverbal clues that people unwittingly drop when they are fabricating a story. Liars will give much shorter answers and they won’t give you any details. There will also be an increase in the length of pauses between words and sentences. Liars can attempt to fill these pauses, for example by repeating the question they were asked. Another indication of someone inventing a story is that they begin to stammer a lot more. All these clues come from the fact that liars only have a very basic version of a story, compared to someone telling the truth.

How our words betray us

The difference between someone telling the truth and someone telling a lie is like the difference between a tree and a broomstick. A tree is a complex organism that has branches, leaves, flowers and fruit growing on it. This level of complexity is also characteristic of a truthful story: there are emotions, interactions, sensory observations, unexpected events. Just like a tree, a true story comes with a lot of details, whereas a broomstick is just a straight piece of wood. It isn’t a complete story. For example, if your spouse says this evening: “I went to drink something with someone somewhere”, then you may want to start asking questions, because a lack of detail could mean there’s only a broomstick, not a tree.

However, a key principle during an interview is to have complete and total belief in the subject. The point is not to look for the lie, but to look for the truth. When you notice there are details missing, you should ask questions. Learn to listen to what wasn’t said in order to discover what was said.

The gardener’s broomstick story

An example of a story without details is from an investigation I conducted a few years ago. A gardener came to report the disappearance of his wife to the police. It was a very nice summer’s day in June and the gardener had taken a nap for about half an hour at four o’clock in the afternoon after which he found his wife missing. However, it was ten o’clock in the evening when the gardener showed up at the police station. When I interviewed him, I asked him: “What did you do from four o’clock until now?” He replied he had done nothing. He hadn’t thought of any details for his story. The gardener only had a broomstick as his story and that gave him away: we found out he had actually murdered his wife.

Truth detection

Any old fool can tell the truth, but you have to be very smart to tell a convincing lie, to make an investigator believe that a broomstick is a tree. Empathize with the subject and have total belief in them, rather than assume they are lying. These are the five things to remember as an investigator:

  • Go to the scene

  • Don’t talk, just listen

  • Assume nothing

  • Focus on body language

  • Seek for the truth

Investigating isn’t about lie detection, it’s about truth detection.