Why Polygraph Tests Are Not Admissible in Court

polygraph test comic

If you watch any TV show about true crimes or a drama, you’ll often see references to polygraph tests.

Given that the criminal justice system relies so heavily on people telling the truth, many people wonder why lie detectors are not used routinely in most cases.

However, in Texas as most states, polygraph results are not admissible in criminal trials.

Although polygraphs are also called lie detectors, in reality a polygraph machine does not have any reliable capacity for detecting the truth or falsity of a statement. The machines measure a person’s biological processes to determine if they are becoming stressed out during interrogations. Factors such as an increase in blood pressure or heart rate are measured. While these may be indicators that a person is lying, they may also simply indicate that a suspect is feeling pressurized by the interrogation even if they are telling the truth. Even if you ‘pass’ a polygraph test, it won’t help you in a criminal trial.

Can You Be Forced to Take a Polygraph Test?

Although police use polygraph tests less frequently than in the past, you might still be asked to take one after an arrest. Although psychological pressure may be provided by investigators, you do not have to take a polygraph test. Many people are not aware of their legal right to refuse.

If you refuse to take a polygraph test, some investigators may become more convinced that you are guilty. However, you are just asserting your legal rights and it won’t help you if you pass it, because the police may simply believe you have beat the test rather than being innocent.

This does not stop many investigators from requesting a lie detector test, often as part of a criminal investigation. There have been examples of interrogators seeking to convince defendants that the lie detector has shown results will be detrimental and they should confess.

Where Polygraph Tests Can be Used as Evidence

In Florida, California, Georgia and Nevada, polygraph tests can be used if everyone agrees to it but there are different opinions on the test’s accuracy. In California lawyers can present the results to the jurors and allow them to make up their minds. Georgia allows defendants who suffer due to a false result on a polygraph to sue the polygraph operator for damages. Florida is the only state that can require some defendants to take polygraph tests – previously convicted sex offenders in this case, although the test results can’t be used in court.

Defendants should always exercise care if they are asked to take a polygraph. You should never submit to an interview or a polygraph without first discussing your case with a Board Certified criminal defense lawyer.

At Broden & Mickelsen, LLP, we are experienced Dallas criminal defense lawyers are dedicated to providing aggressive and ethical representation to individuals and businesses charged with crimes.