Why lie detection methods fail

On Behalf of | Feb 1, 2024 | Criminal Defense |

Louisiana prosecutors and other law enforcement authorities deploy any number of techniques and methods while trying to apprehend and convict suspects. Some are concrete evidence-based, like fingerprints or other physical markers. But just as important – if not more important – is evidence gained by questioning suspects and witnesses.

Refuting witness testimony or accounts of a suspect’s conversations with law enforcement is a key part of any criminal defense strategy. And it starts with an understanding of the true limits of certain techniques. Lie detection methods in particular are highly unreliable, despite frequently being used in court.

Common lie detection methods

The two lie detection methods law enforcement uses are lie detectors (often referred to as as polygraph tests) and behavioral and body language analysis. Both have significant flaws.

A polygraph test measures a person’s physiological arousal while answering questions. The theory goes that those who are lying will experience signs of greater distress or arousal than those telling the truth.

Behavioral analysis involves a trained observer noting certain cues, both verbal and non-verbal. The observer is trained to notice cues consistent with how people who are lying often behave.

Why these methods fail

In the case of polygraph tests, the fundamental flaw is that physiological arousal isn’t exclusive to people who are lying. Being questioned by law enforcement is highly stressful, and even honest people can often exhibit the kinds of signals that polygraph operators would note as signs of deceitfulness.

Behavioral analysis is even more dubious. While law enforcement has researched and bankrolled extensive programs attempting to create reliable results, these techniques have repeatedly failed to produce good, consistent results in the real world. In the end, these techniques aren’t “scientific” at all, and shouldn’t be treated as such.


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