We know that people tell a lot of lies based on a variety of motivators. And, we know there are different types of lies ranging from the seemingly innocuous white lie to the blatant bald-faced lie. So, how do we know when someone is lying?  Unfortunately, people are not like Pinocchio where their noses grow when they lie. This would be too easy. The spider senses may tingle when someone is lying to us or we may get a gut feeling that something is askew but these methods of detecting deception are not scientifically-based and reliable predictors of truthfulness.
Former CIA employees Philip Houston, Michael Floyd and Susan Carnicero, in their book, Spy the Lie, argue that if you want to know if someone is lying, you need to ignore and not process truthful behavior. Instead you need to focus on behaviors that are associated with a question or, as they call it, a stimulus. They claim it’s the question or statement that stimulates the potentially deceptive behavior. 
To determine if someone is trying to deceive us, we need to employ the L-squared method where we look and listen simultaneously. The trick is to look for a cluster of behaviors; a cluster is any combination of two or more deceptive indicators that are either verbal or nonverbal. The larger the number of deceptive indicators, the greater the chance of deception. If there is a single deceptive behaviour, ignore it.
Here’s how it works
You ask the interviewee a question. You go into L-squared mode immediately; look and listen for clusters of deceptive behavior. The first deceptive behavior has to occur within the first five seconds of the stimulus – either in the form of a question or statement. The cluster is comprised of the first behavior and all behaviors following it until it the stream is broken by another stimulus or interruption.
An example
You are interviewing a person of interest in a theft.  You ask the following question:
                     Did you steal the laptop?
                    Within 5 seconds, the person of interest responds:
I go to church every Sunday. I swear on a stack of Bibles that I am not a thief.  (This is a religious deception. A lack of contraction for “I am” is also another deception ploy. (More on these deception techniques in future posts.)
The person of interest starts to move around in the chair, bounces his/her right leg up and down rapidly, and breaks eye contact with the interviewer. In addition, the interviewee starts to rub his/her eyes.
You have been provided with a cluster of behaviors, verbal and nonverbal, the first of which began within five seconds. However, this doesn’t mean you have definitive proof the person is lying. What you have may be strong indicators of deception, but you still need to follow up and drill down with more questions. The clusters are red flags – an invitation to explore the responses in detail. Be curious.  Ask lots of questions. Peel back the layers of the onion.