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Criminal Law Blog

FAQs About Lie Detector Tests in Criminal Cases

January 14, 2022

Chances are that you have seen movies or TV dramas in which an accused person takes a lie detector test and is exonerated of a crime or arrested on the spot. In real life, things aren’t quite so simple. Lie detector tests—or polygraph tests—are not reliably accurate, so there are strict rules regarding how they can be used in criminal cases, particularly when it comes to admitting the results in court. The first thing you should know about lie detector tests is that you should never consent to one without the advice of a criminal defense attorney. In addition, you should have your attorney present for the test if you do take one. 

If you’re considering taking a lie detector test because of criminal charges you are facing, here are the answers to some questions that may be on your mind. 

How do lie detector tests work?

Lie detector tests measure physiological responses to questions asked by a trained test administrator. The idea behind the test is that you will show a physiological response that you cannot control when you answer a question untruthfully, such as an increase in blood pressure and respiratory rate. When you’re telling the truth, you won’t experience these symptoms. 

The problem with this is that you can have these kinds of nervous responses for many reasons. You may simply be nervous to take the test, or you may have a physiological response to a question about your involvement in a crime even when you are answering truthfully, because you are reacting to the seriousness of the question. Additionally, there is no scientific evidence confirming that lie detectors can accurately detect when a person is lying. 

Why does anyone use lie detectors if they are not accurate?

Some people believe lie detector tests are a helpful investigative tool. Police officers may suggest using a lie detector test to implicate or clear suspects in a crime or to help guide their investigation. Some people in the law enforcement community believe that lie detector tests are accurate more often than they are wrong, while others find them useless. 

As a baseline, police officers cannot use a lie detector test on suspects without reading them their Miranda rights. If you are being asked to take a test, never agree without consulting your attorney, even if you think the test could prove your innocence. 

Can a lie detector test be used in court?

The Supreme Court has ruled that different jurisdictions have the right to decide their own rules about lie detector tests, so the admissibility of the tests in court depends on where you live. In Arizona, lie detectors can be used in court if both parties agree to admitting the results into evidence. However, even if both parties agree, the judge can still overrule that request and refuse to admit the results. 

Using the results of a lie detector test in a criminal court case is a decision that should only be made with careful consideration with your defense attorney. Even if the results of the tests are in your favor, using them in court could open you to different lines of questioning that could jeopardize your case. 

Can I be forced to take a lie detector test?

You cannot be forced to take a lie detector test. The police may tell you that you’ll be arrested if you don’t take the test or that taking the test is the only way to end your questioning, but you cannot be legally compelled to take one. Even if you know that the test results cannot be used in court without your consent, they can be used as an investigative tool in building a case against you, so always refuse a test unless your criminal defense attorney explicitly tells you otherwise and is present for the test. 

If you do take the test, answer only the questions you are asked. Beware the post-test interview period when you are disconnected from the machine. Statements you make during that time can be used against you, and many subjects make the mistake of speaking too freely, because they believe the test is over. This is another reason that it is crucial for your defense attorney to observe your test, so that he or she can ensure your rights are preserved throughout the process. 

If you are arrested, everything you say and do could impact your ability to fight your charges. Don’t make the mistake of trying to talk your way out of an investigation. Instead, call Tucson criminal defense attorney Janet Altschuler before answering questions from law enforcement officers. She will protect your rights from the start of your case to ensure you get the best possible outcome. If you are facing criminal charges in Tucson, call (520) 829-4460.

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