Imagine that you are accused of a crime that you did not commit. The detective that is investigating the case tells you that, if you really didn't do it, you should just take a "lie detector" or polygraph test to prove your innocence. Is this a good idea or not?
Before I give my response to that question, I need to point out that every situation is different, and I am speaking in general terms. The specific circumstances of your individual case might be exceptional. The only way to know for sure is to consult with an experienced criminal defense attorney. If my comments differ from those of your own lawyer, please remember that he or she knows the specifics of your case better than I do, and his of her advice is more specifically tailored to the facts of your case. So, please don't let this blog be a substitute for your own lawyer's professional judgment.
With that caveat out of the way, my answer is generally "NO". And, if you have not yet had an opportunity to meet with a well-qualified, experienced criminal defense lawyer, my answer is definitely, "NO". I generally advise against polygraph tests for a few reasons:
1. Polygraphs are unreliable.
Supporters of polygraph testing claim that it is about 90% accurate. Other evidence suggests that polygraphs are considerably less accurate than that. But, for the sake of argument, let's assume there is merit to the 90% argument even though, personally, I highly doubt that they are anywhere near this accurate. This would mean that if you, as an innocent person, take a polygraph to "prove" your innocence, there is at least a 1 in 10 chance, you will inadvertently "prove" your own guilt. And, that's using the polygraph supporters' own argument.
If you are accused, or even suspected, of a crime, you have a right to remain silent in order to ensure that you don't accidentally say something that sounds incriminating. You also have the right to have a lawyer present if you do choose to say something. Our legal system is designed so that you are not required to prove your innocence; and, a lack of evidence points to legal innocence, not guilt, under the law. So, my question, in most circumstances is this: Why would you willingly surrender your right to remain silent and your right to have an attorney present during questioning (which is typically required during a polygraph test), in order to "prove" something that you're not required to prove, when there is AT LEAST a 10% chance, you will accidentally "prove" your own guilt (even though you're innocent)?
Unlike the images of lie detectors that you may have seen in children's cartoons, a polygraph test does not simply produce a green or red light that says "truth" or "lie". Rather, the "science" behind a polygraph requires readings of various signals of biological stress. To translate these various signals requires that a trained person interpret the results and form an opinion as to whether the results are more consistent with a person who is telling the truth or a person who is lying.
Usually (but not always), polygraph tests are performed by an employee of the police department that is investigating you, usually a trained police officer and often, a detective. Therefore, when you take a polygraph at a police station, you are asking a person who works for an agency that already believes that you probably committed a crime to subjectively analyze the results of your polygraph test and conclude that they've got it all wrong. As strange as it sounds, it sometimes works out that way; but, more often, it does not, either because of bias or because of the inaccuracy of the test itself.
3. Polygraphs are coercive.
The worst part of a polygraph is often not the test itself, but the aftermath. When the test is administered by a detective or other police officer, the test is often merely a pretense to convince you to say something that can later be used against you. In fact, the results of the polygraph test itself are not admissible in court.
But, imagine that you've just been hooked up to various instruments designed to measure your respiration, heartbeat, sweat, etc., and asked a series of yes or no questions about the worst thing you could imagine being accused of. After you are done, the detective administering the test says, "Well, the polygraph says you're lying, so now is the time to tell us what you were lying about." Suppose you remember that somewhere along the line one of your answers was only partially accurate, so you say, "It must have been the question about __________. I guess I should have said yes." Now, although the results of the polygraph are not admissible in court, your "confession" that you had made an untruthful statement to a police officer is. There are some people who may be prone to give into this pressure so much as to make up something that they "lied" about.
Although the script varies, I have had several clients who have been sucked in by this strategy. It doesn't particularly matter whether the polygraph actually indicated lying or not, there is nothing to keep a police polygraph examiner from using the post-polygraph interview as a means to extract a "confession", or at least a statement that ends up looking bad in court.
As I'm sure I've made clear, I am not a fan of polygraph testing. There may arise a rare instance here and there where it is an appropriate method to get a prosecutor to back off on criminal charges. But, more often, it is designed as a tool to convince accused people to make statements that help the police and the prosecutor build their case. If you are asked to take a polygraph, always talk to a good criminal defense lawyer first, who can help you decide if the benefits outweigh the risks.
If you have been accused of a crime and need help protecting yourself while the police investigate or the prosecutor prosecutes, please give us a call or visit our criminal defense page.
If you have been convicted of a crime and you believe that the police, prosecutor, or judge may have caused you to be denied a fair trial, please call us of visit our felony appeals page.
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