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Can a Lie Detector Test Prove Innocence?

It’s a classic cop show trope.

A grizzled detective with a five o’clock shadow and a slightly reddened nose leans over a table in a police interview room. On the other side is a suspected criminal who refuses to talk. His arms crossed and eyes narrowed, daring the detective to keep trying. Then, the detective threatens to bring out a lie detector test, and the suspect suddenly looks terrified.

Lie detector tests, also known as polygraphs, were invented in California in 1921 and ever since have been thought of as a nearly-flawless interrogation tool.

Is it, though? Are there ways to beat a polygraph exam? Can a lie detector test prove you innocent?

We talk more about that in this article. So read on!

How Does a Lie Detector Test Work?

Polygraph exams supposedly measure a set of involuntary body functions to determine if a person is lying. These functions are pulse, blood pressure, rate of respiration, and skin conductivity. All of these play a crucial role in anxiety, which most of us will have when lying.

This is measured using blood pressure cuffs and other monitors. This is why you often see images of people hooked up to stickers, electrodes, and similar equipment when taking a lie detector test.

The Polygraph Test and Anxiety

How accurate is a lie detector test? It’s hard to determine because there is a significant flaw that comes into play here. Anxiety occurs in many different situations, including, for instance, when police are questioning you.

There’s also the issue of anxiety disorders, which make it far less likely that the person in question will pass the test. Anxiety disorders are often thought of as a single condition that simply involves being excessively nervous in certain situations.

While that is true for some types of anxiety, there are other disorders we don’t often think of as a type of anxiety. In addition to the ones we usually associate with anxiety, such as Generalized Anxiety Disorder and Social Anxiety Disorder, there’s also Panic Disorder, Obsessive-Compulsive Disorder (OCD), and Post-Traumatic Stress Disorder (PTSD).

Polygraphs can’t prove guilt, but what’s the relationship between a polygraph test and innocence?

Polygraphs and Psychopathy

While nervous people often fail polygraph exams, certain other types of mentally ill people have a good chance of passing the test even if they’re lying.

Psychopaths, for instance, experience little to no guilt, so their bodily responses wouldn’t seem abnormal on a polygraph. There have been several instances of psychopaths beating polygraph tests.

Polygraph tests function by using simple questions with verifiable answers to establish a baseline, such as, “When is your birthday?” or “What is your full name?” If your baseline is the same as when you’re lying, the difference won’t be detected.

Mental Health and Management

While several mental health conditions can affect lie detector test results, many claim that they won’t, so long as the person in question is being properly treated and medicated.

Unfortunately, anti-anxiety medications can also affect polygraph results, as can many other kinds of drugs, both legal and illegal.

Even neurotypical individuals can accidentally cause a false positive. The test responds to nerves and guilt, so feeling guilty for any reason can tamper with it. Perhaps the person you’re questioning witnessed the crime while on the way to see their mistress.

Examiner Error

Another factor that can muddle the test results is the examiner’s skill and experience. Since a polygraph exam measures bodily reactions, it will be useless to anyone who doesn’t know how to read it.

While examiners do go through some training, it’s not always easy to read a polygraph, and several things can throw off the results. The polygraph results can come out inconclusive. Which means that they can’t interpret the results accurately.

The Court Weighs In

The polygraph test was admissible as trial evidence nationwide for several decades, but that changed in 1998 when the Supreme Court decided passing a polygraph didn’t count as evidence.

These days, most states don’t even allow polygraphs to be presented as evidence in court. Of the 23 that do, many of them have imposed standards for when and how they can use a polygraph. For instance, they can’t portray the test as flawless, and all parties must consent to the test.

Given the dubious status that polygraphs hold in court, you shouldn’t be intimidated if an officer tries to scare you into a plea deal. They have no ground to stand on.

Know Your Rights

No matter who you are, it’s essential to know your rights. There are certain things the cops aren’t allowed to do to a person. Regardless of the charges.

One of the biggest, and most common rules police officers break, is intimidating or threatening you into a confession. If a cop ever tries to get you to confess by warning that you’ll need to take a lie detector test if you don’t, ignore them.

A polygraph exam is not required during an investigation. So, if the cops threaten you by telling you the test is mandatory, it is a lie. And, any evidence obtained illegally is not admissible in court. Thus, they can’t hold refusing to take a lie detector test against you.

Can a Lie Detector Prove Innocence

Is there a correlation between the results of a lie detector test and innocence? The best answer we can offer to this is maybe. There does seem to be a correlation between dishonesty and primary nervous function, but the whole story is far more complicated.

People often feel nervous and guilty when they lie, but they can feel anxious about countless other things as well. Meanwhile, some people won’t feel guilty and, therefore, won’t trigger the test.

Other factors, such as medicine and poor instruction, can influence the results.

If you need to understand how the legal process works or want to hire a lawyer, learn more about our team on our website.


RHINO Lawyers can help and guide you through a system molded by law enforcement, judges, and lawyers for decades. Having won cases for our clients in similar circumstances, our criminal defense team knows what it takes to fight on your behalf.

Let RHINO Lawyers answer your questions and review the facts of your case with a Free Consultation. So, get started by completing the “Free Instant Case Evaluation” or by calling us any time, day or night, at (844) RHINO-77.