The Common Law

The judge is the gatekeeper for the admissibility of evidence in court. Judges decide what evidence the jury will consider and what evidence each side may present at trial. In the past, lie detectors, or polygraphs, have not been admissible at trial in most states. Many courts considered them unreliable because the scientific community did not generally accept them. In the past decade, however, some courts have re-evaluated their position regarding the use and admissibility of lie detector results.

The traditional rule for expert and scientific testimony was that it had to be generally accepted by the scientific community in order to be admissible at trial. The modern trend is that polygraphs may be introduced to the jury if it will assist them in deciding a fact and it tends to support the conclusion it purports (i.e., if it is reliable and relevant).

For example, the Supreme Court has been divided on the issue of polygraph evidence. The justices do, however, generally agree that polygraph evidence is no longer unreliable, should not be automatically banned from the courtroom, and does not cause the jury to substitute the polygraph determinations for their own. Accordingly, most jurisdictions no longer have a complete ban on polygraph evidence in the courtroom, but there are still evidentiary hurdles for the evidence before either side can effectively use polygraphs at trial.

Texas courts have historically been hostile to the introduction of polygraph evidence at trial, but the Rules of Evidence reflect the trend that judges may not completely exclude polygraph evidence from the courtroom. Many judges fear the impact a polygraph may have upon the verdict because juries view lie detectors as a strong indicator of truth. However, juries decide matters of fact and therefore can determine how much deference to give to scientific evidence such as polygraphs. Ultimately, judges use their own discretion in determining whether to admit polygraph evidence.