Are Polygraphs Admissible in Court?

Polygraph machines are sometimes referred to as lie detectors” although research has failed to provide evidence that they are reliable enough in identifying deception for polygraph test “results” to be admissible in a court of law. But there is more to know about how polygraph technology is being used in the United States criminal justice system, including the rare circumstances when polygraph test evidence may be admitted into evidence. 


This blog post explains how polygraph tests are conducted, what information they produce, why they are virtually never admissible as evidence in court, and how some test subjects can successfully cause the polygraph to mislead the polygraph operator. At Stechschulte Nell, Attorneys at Law, here in Tampa, we want all our clients and the entire community to understand the law as it relates to polygraph tests.  


Only by being armed with accurate information about the law can you make the best decisions to prevent the violation of your legal rights. If you or your family member need answers or legal help defending against criminal prosecution, contact Stechschulte Nell 



How Do Polygraph Machines Work? 


The theory underlying polygraph technology is that when people experience stress, their bodies react in ways that can be monitored and measured. Under certain stressful conditions or periods of “physiological arousal,” our hands may sweat more than usual, and we experience changes in our heart rate, respiration, and blood pressure. In theory, our cultural pressures to be truthful and sense of guilt cause us to display different reactions when we lie than when we tell the truth. 


The polygraph machine uses sensors attached to the finger, chest, and arm that transmit electrical impulses that are reflected by a series of graphs corresponding to each of the sensors. The polygraph operator asks a series of test questions including some that they want the person to lie about. That shows the operator how that person’s deception registers on the graph. 


Then, the operator asks the test subject a series of yes or no questions about the crime being investigated mixed in with some questions that do not stimulate stress. At the end of the test, the polygraph operator scores and “interprets” the graph produced during the test. Theoretically, a well-trained polygrapher who conducts the test according to the proper protocol will be able to determine whether the person was deceptive or not.  


Sound too good to be true? According to current law, polygraph theory is not true enough. 


Learn More > How Polygraphs Work  


Is Polygraphy Evidence Ever Admissible in Court? 


The answer is rarely. But, the U.S. Circuit Court for the Eleventh Circuit has ruled that polygraph evidence may be admitted only if both parties agree that the results will be admissible before the test is conducted, including who will conduct the test, and what questions will be asked.  


The court ruled that a universal rule barring any use of polygraph evidence is inconsistent with the Daubert standard which requires the admissibility of scientific evidence to be decided based on expert testimony as to its general acceptance by the scientific community, whether it was peer-reviewed, its known error rate, and other factors. Even then, other evidentiary hurdles must be overcome before either party may put polygraph-related data into evidence.  


Why Is Polygraph Evidence Not Admissible in Court? 


As we explained above, the polygraph test “results” are interpreted by the trained examiner. That “interpretation” can vary between different examiners, making the conclusions about whether a test subject “passed” or “failed” too subjective and unable to be confirmed.  


Another reason polygraphs are not deemed reliable enough for use in court is the fact that individuals react differently under similar circumstances. One subject may be prone to spikes in anxiety regardless of their surroundings or the nature of the questions they’re asked. Someone can feel pangs of guilt when no such guilty feelings are reasonable. Someone else could have a depraved lack of conscience and feel no guilt, shame, or stress when being questioned about crimes they committed.  


In short, the underlying theory that people display measurable, identifiable physiological reactions to stress during deception simply does not apply to everyone. 


Why Are Polygraph Tests Used By Police If They Are Not Admissible in Evidence? 


The fact that polygraph evidence is not reliable enough to be used as evidence in court does not necessarily mean that the technology has no value at all. Federal, state, and local law enforcement use polygraph tests fairly frequently.  


The effectiveness of polygraphs for investigative purposes comes from the popular belief that the “lie detector” actually works. Investigators report that criminal suspects who agree to undergo a polygraph test sometimes confess because they believe the test will expose them as liars if they deny their guilt. In other cases, a suspect will take the polygraph test and have confidence that they “passed” only to be told by police that the test “proved” they were lying. 


“We know you’re lying. The test proved it. Why don’t you just confess?” We know that this interrogation technique does result in suspects ultimately confessing, even if they are innocent. 


In still other cases, police use polygraph tests to narrow down suspects. If several suspects agree to be tested on the polygraph machine and one person refuses, police will often conclude that person is hiding something, probably guilt. 


Defense Use of Polygraph Tests to Prove Innocence 


Some defense lawyers find polygraph tests to be useful for their clients in demonstrating to police that they are not guilty of the suspected crime. This defense technique involves the lawyer hiring a professional polygrapher to test the client in private. If the client scores as “not deceptive,” then the lawyer will share the results with law enforcement and prosecutors, waving the results around for all to see. If the client’s test is consistent with deception, then the entire test event is kept confidential and never disclosed.  


Learn More > Should You Take a Lie Detector Test to Prove Your Innocence?  


Never Consent to a Polygraph Test Until You Consult an Experienced Criminal Defense Lawyer 


Polygraph tests are of limited value and should only be used after fully consulting with your criminal defense lawyer, if ever. There is never a good reason to consent to a polygraph test performed by the police or by a police-hired polygrapher. Even if you do answer all questions truthfully, the police are permitted to lie to you about the results of the test. 


If you need more information about polygraph tests in Tampa or St. Petersburg, contact the experienced criminal defense lawyers at Stechschulte Nell. We are ready to help you. Call 813-280-1244 today.  

To learn more about how we can help

Contact us Today