South Carolina Criminal Defense Blog

Polygraph results have consistently been held by the courts to be inadmissible at trial. There are some jurisdictions that allow them under limited circumstances, but in most jurisdictions they are per se inadmissible. The science has not been proven to be reliable, even under the most lenient standards, and the danger of unfair prejudice (confusing and misleading the jury) greatly outweighs any probative value.

Every so often a defense attorney will have a client that passes a polygraph, or a co-defendant or third party that fails a polygraph, and they want desperately for the jury to hear these polygraph results. I have had both situations and have used the polygraph results in pre-trial negotiations, but resist the urge to ever ask a court to admit the results in front of a jury. This is a two-edged sword, and the government’s side of the blade cuts deeper than the Defendant’s. If the courts begin to admit polygraph examinations for defendants, they will surely begin to admit them for the government as well, and you can bet it would happen loud and often.

What are the problems with polygraph examinations? First of all they are not reliable. Contrary to popular belief, they do not tell the examiner whether the subject is telling the truth or lying. They can indicate deception based on physiological reactions to the questions posed, but even an indication of deception or lack of deception can be skewed by an individual’s physiology or the bias of the examiner. Some people are inherently nervous, and others are unshakable. Some people can control their physical reactions.

My biggest problem with polygraph examinations by the government is that they are often nothing more than an interrogation tool. While polygraph results are not admissible in court, statements made by the defendant during the course of the examination probably are admissible. A common tactic is to wire up the subject, begin questioning him or her, tell them that the machine proves that they are lying, and then continue interrogation of the subject until a confession is obtained.

Often clients insist that they want to take a polygraph for the government, to prove their innocence. And I don’t blame them – it may be that they know that they are innocent, and they are convinced, like most people, that polygraphs are infallible lie detector tests that will prove their innocence to the police or the prosecutors. They don’t understand that 1) under the best of circumstances the machines are not 100% reliable, and 2) in the eyes of an FBI agent, SLED agent or investigator for the local sheriff’s department, they are guilty and the polygraph is nothing more than a tool to obtain additional evidence.

This is not to say that polygraphs are not useful, because they are. We use respected independent polygraph examiners in some cases, where a client insists on a polygraph, but rarely will we consent to allow a government polygraph/interrogation. If the results from the independent polygraph examination show no deception, we will allow the government’s examiner to review the charts and discuss the interview with the independent examiner. If the results are not favorable (this does not necessarily mean that the person is guilty), the government does not need to know about it and they do not then have the opportunity to interrogate the client.