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

Anyone thinking about “taking a lie detector test” needs to read this blog post before doing anything else. Many people misunderstand the machine referred to as a lie detector, and they mistakenly believe that the apparatus can actually identify a falsehood hidden among an otherwise truthful conversation.  


The three most important points to remember: 


  1. No one in Florida is required to submit to a “lie detector” test (polygraph).i 
  2. There is no such thing as a “lie detector” machine. 
  3. Contact an experienced criminal defense lawyer if you want to take a polygraph test. 


No such equipment exists. What is often called a “lie detector” is a device more accurately termed a “polygraph” or a “polygraph machine.” And it is exactly that; a machine that produces many (poly means “many” in Greek) graphs on a scroll of paper that is then interpreted by a trained “polygrapher” who operates the equipment during the test. 


Before we explain how a polygraph test works (or doesn’t work), you should know what function the polygraph frequently serves in both civil and criminal investigations. There’s a popular impression that sitting down with an expert polygrapher who then hooks you up to a sophisticated piece of equipment with highly sensitive sensors will expose them as liars. As a result of the common fear that the machine will catch them anyway, lots of people confess even before getting attached to the polygraph. Others confess after the test is complete and they are informed (even falsely) that the machine indicated they were lying. 


One of the most reliable powers of the polygraph process is the ability to encourage confessions. 


What Does a Polygraph Machine Measure? 


A polygraph test is conducted by a trained polygraph examiner who connects electronic sensors to your body to measure your physiological reactions to questions they ask you under controlled circumstances. The examiner will explain the process to the person being tested, then attach the sensors as follows: 


  • fingertips – measures skin conductivity (galvanic skin or electrodermal response from sweat) 
  • around chest – measures rate and intensity of breathing 
  • around upper arm – measures heart rate and blood pressure 


The polygrapher asks test questions in which you are asked to lie so the examiner can see how the graph records your physiological responses when you lie.  


When the actual test begins, the examiner asks yes or no questions in a calm manner, ideally with only the two of you in the room. The theory is that guilty people display measurable signs of anxiety when they are confronted with a question they answer falsely.  


The obvious problem is that even innocent, truthful people become anxious when asked certain questions about sensitive topics.  


Learn More> How Polygraphs Work  


Why NOT Take a Police Polygraph Test 


If you are asked by law enforcement officers to take a polygraph test, you should not do so. You should decline and immediately contact the best, most experienced criminal defense lawyer you can find. 


Many police requests for a suspect or a witness to take a polygraph test are to find out if they are willing and how they behave when asked to take the test. These two reactions can influence how the police investigators perceive the person. Again, the person’s reactions are generally based on their belief that the polygraph test is a reliable detector of deceit. 


Examiner’s Bias — The polygraph machine itself is nothing but an instrument that makes graphs. It is the polygraph examiner’s interpretation of the graph and the questions asked during the questioning that determines whether the person “passed” or “failed.” A polygraph examiner with poor technical or poor analytical skills will produce a useless test result. A biased examiner will also produce a worthless test result.  


Intentionally Misleading Test Results — If police develop strong evidence of guilt against a suspect, the suspect’s “passing” a polygraph will not convince the police to declare the suspect innocent. Instead, they will simply discount the polygraph as ineffective and inaccurate. 


However, police are legally entitled to lie to a suspect they are interrogating. If the suspect passed the polygraph test, the police could simply falsely inform the person that they failed. The purpose of the deceit is to convince the suspect that the “scientific machine” caught them in a string of lies. Since they are now proven to be lying, as the strategy goes, the suspect may give up the pretense and confess. 


Such a scenario is not common, but it has occurred often enough to encourage police to try the tactic. 


Hiring Your Own Polygraph Examiner for the Defense 


While you are wise never to agree to a police-led polygraph test, experienced defense lawyers sometimes find it useful to hire a polygrapher to conduct a test on their client.  


Why get a defense polygrapher? — Although polygraph test results are not admissible in court for either the prosecution or the defense, a defense-conducted polygraph test can have value.  


If a well-respected polygrapher gives the defense attorney a report declaring that the defendant’s answers showed “no sign of deceit,” an experienced criminal defense lawyer will notify the prosecution and argue that the test proves the defendant is innocent.  


A test result that shows the defendant is not deceptive does not prove innocence, but it might plant the seeds of doubt in the mind of the prosecutor or the police. If the prosecution senses the state’s case is less well founded than they thought it was, the prosecutor may consider negotiating a more favorable disposition for the defendant.  


When a defense-conducted polygraph test indicates the client is providing deceptive answers, the test results are not required to be disclosed to anyone. They are confidential defense work-product.  


The results of a polygraph test are as valuable and as convincing as the person using the test can make them.  



Beating a Polygraph Machine 


Because the polygraph machine measures physiological responses and moves a needle on a sheet of paper that creates a graph, someone who can manipulate their bodily responses can distort the movement of the needles and the graph.  


Polygraph equipment and the “science” is based on the premise that humans react to stress and anxiety in a predictable, measurable manner. But we know from long experience that some people can perform heinous acts without remorse and move forward with their lives with a clear conscience.  


Contact Tampa’s experienced criminal defense lawyers for polygraph advice. Call Stechschulte Nell, Attorneys at Law today; 813-280-1244. 

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