Can I Prove My Innocence by Taking a Lie Detector Test?

Lie detector tests, or “polygraph examinations,” as they are more formally known, are commonly seen in countless TV shows and movies, and have become widely recognizable in our popular culture as an integral part of our criminal justice system. This leads many to believe that they may be used directly to prove one’s innocence or guilt in a criminal case. However, due to legitimate concerns of their unreliability and their somewhat subjective nature, they are inadmissible in court in most states, or subject to strict rules, governing their use in court.

A polygraph machine is used to detect and measure an individual’s physiological responses, such as perspiration, pulse rate, breathing, blood pressure, and other involuntary bodily changes, as signs of the person’s untruthfulness. These examinations are based on the concept that an individual exhibits certain biological responses when giving untruthful answers that differ ostensibly from those exhibited when answering truthfully. Much of the scientific community considers polygraph exams to be unreliable, generally, due, in large part, to the notion that the nature or tone of the person administering the test can significantly affect the test results, or that the stress induced by the examination itself could easily compromise the results.

The admissibility of a polygraph test in court varies from state to state. However, admissibility falls generally into two main categories: states that find the results of the test entirely inadmissible, and those that allow them in court, but only if it is submitted with stipulations from the parties — that is, that both the defense and the prosecution are required to consent to the admission of the test results in the proceeding.

Approximately half of the states consider polygraph tests to be admissible in court (in both criminal and civil cases), subject to certain stipulations. The majority of those states require the approval of both parties before they can be admitted in court. In Pennsylvania, lie detector tests are inadmissible in court, even if both parties consent.

Polygraphs are commonly used as part of the screening process for certain types of jobs, such as law enforcement, particularly for jobs in security and handling drugs or in investigating a specific theft or other suspected crime, and some high-level security positions.

While there are significant limitations on their use in court proceedings, polygraphs are commonly used as part of a criminal investigation, giving rise to concerns of unfair police practices or potential overreach by law enforcement personnel. When administering a polygraph, interrogators often attempt to convince the person undergoing the examination that the lie detector test has revealed results that inculpate the test subject, and that he or she should confess to the crime, which results in a large number of people making confessions, even when their exam results demonstrated no conclusive signs of deception or falsehoods.

In addition, while the results of the test cannot inadmissible in court, any statements made by the test subject before or after the polygraph examination are admissible. The test administrators are well-trained law enforcement officers, who are able to ask questions before and after the examination that induce individuals to make statements, unintentionally, that can incriminate them. Further, statements made during the exam could also lead the police to other evidence that they can use to convict them.

If you or a loved one are involved in a case in which you are asked to take a lie detector test, or the results of a lie detector test are being used against you, the attorneys at Tanner Law Offices can assist you or your loved ones in the process of defending against criminal charges and in protecting your rights. Please contact our office at 717-836-0471 to schedule a consultation to discuss your case.