Polygraph tests, also known as lie detector tests, have been used as a tool in criminal investigations since the early 20th century. The test measures an individual's physiological responses, such as heart rate, blood pressure, and perspiration levels, to determine whether they are truthful or deceptive during questioning.
However, the accuracy and reliability of polygraph testing have been a subject of debate among legal professionals and psychologists for decades. Therefore, while polygraphs are still used in criminal investigations and trials, California law restricts how they may be used in court.
In other words, a polygraph test is only admissible in court if all parties agree to admit it into evidence. Police can't force a suspect or witness to take a polygraph. A polygraph test is when an examiner asks questions to determine if you are telling the truth. This test is often given to defendants and witnesses in criminal cases.
A polygraph is an electrical device that is supposed to measure your biological changes when you answer questions from the examiner. In theory, these changes indicate when you are likely telling the truth or a lie.
Numerous studies have shown that lie detector tests are not always reliable. Thus, the polygraph test results are not admissible as evidence in a jury trial unless the defense lawyer and prosecutor agree to have the results admitted.
Most criminal defense attorneys will advise their clients never to submit to a police polygraph without guidance from their legal counsel. However, sometimes, you could take a private polygraph test to prove your innocence. Let's review this topic in more detail below.
California Law and the Admissibility of Polygraph Results
In California, the general rule is that polygraph test results are not admissible as evidence in criminal trials. The only exception to this rule is if the prosecution and the defense agree to admit the evidence (test results) to be shown to the judge or jury.
Also, an agreement must be reached before the following can be admitted into evidence in court:
- That you were offered to take a polygraph,
- That you took a polygraph test.
- That you refused to take a polygraph test,
- That you failed the polygraph test,
- The opinion of a polygraph examiner.
In addition, the law protects your right to refuse to submit to a polygraph test by law enforcement or prosecutors.
Why Are Polygraph Tests Restricted in Criminal Trials?
There are two primary reasons why the courts do not permit lie detector test results to be admitted into evidence without the express approval of both sides: the unreliability of the tests themselves and the protection of the defendant's rights.
Polygraph Tests Are Not Completely Reliable
Polygraph tests are not foolproof and have been known to yield false results. Some reasons why:
- Subjectivity: The interpretation of polygraph results largely depends on the examiner's subjective analysis of the physiological responses measured during the test. Different examiners might draw different conclusions from the same data, leading to inconsistencies in the assessment of truthfulness or deception.
- False positives: Polygraph tests can produce false positives, where an honest person is wrongly identified as deceptive. This can happen due to various factors, such as nervousness, anxiety, fear, or other emotional reactions unrelated to deception.
- False negatives: Conversely, polygraph tests can also produce false negatives. Some individuals, particularly those with experience in deception or sociopathic tendencies, may be able to control their physiological responses or use countermeasures to manipulate the test results, thus "beating" the polygraph.
Polygraph Tests May Violate Your Constitutional Rights
As a defendant in a criminal case, you have certain fundamental rights that the United States Constitution protects.
These include the right to remain silent (Fifth Amendment) and the right to an attorney (Sixth Amendment).
The administering of a polygraph test does not necessarily uphold these rights. During a polygraph examination, the examiner may ask questions that could potentially incriminate you.
While you have the right to remain silent and not answer these questions, doing so may affect the test results and lead the examiner to conclude that you are deceptive.
Furthermore, while you have the right to an attorney during interrogations, your attorney can only adequately represent you or interject during polygraph examinations if the test only monitors your responses.
How Can Polygraphs Be Used in Criminal Cases?
Although the admissibility of polygraphs is limited during a trial, they can still be utilized only with the consent of the party being questioned in the following ways:
- Plea negotiations: Polygraph results may be used during the negotiation process between the prosecution and defense to determine the credibility of a defendant's statements or to facilitate reaching a plea agreement.
- Pretrial hearings: With both parties' consent, polygraph test results can be admitted as evidence during pretrial hearings to help establish the admissibility of other evidence or to assess the credibility of witnesses.
- Witness questioning: The prosecution and defense may ask potential witnesses to submit to a lie detector test during vetting to determine their viability as witnesses.
- Private polygraph to exonerate the defendant. You have the right to arrange your own lie detector test and submit it as evidence of your innocence. This is often used as an effort to get charges dismissed during the pre-trial phase.
- Parole hearings: In some cases, parole boards may consider polygraph test results when evaluating an inmate's suitability for parole, particularly in assessing their truthfulness about rehabilitation efforts or remorse.
- Sex offender registration proceedings: Polygraph tests may be used to monitor compliance with registration requirements and treatment programs for convicted sex offenders as part of their post-conviction supervision.
- Investigative tool: Although not admissible in court, law enforcement agencies may use polygraph tests during criminal investigations to obtain information, verify suspects' statements, or narrow down the list of potential suspects.
Consult with a Criminal Defense Lawyer and Know Your Rights
Remember that if the police ask you to take a polygraph test, you always have the right to refuse—and in many cases, if not most, it's inadvisable to submit to one.
Even though the test results themselves would not be admissible in court, anything you say during a police-instigated polygraph test could still be used against you in a court of law.
As noted, you can take a private polygraph to prove you are innocent, which is taken when a private polygraph examiner conducts a lie detector test. It can be given to a defendant or witness in criminal cases.
The test is considered “private” because you are not obligated to tell the prosecutor or law enforcement authorities that the test is taken.
Suppose the results of the private test are favorable. In that case, they can be given to the prosecutor in an attempt to get the charges dismissed. Suppose the test results are unfavorable. In that case, it can be kept confidential.
Always consult an experienced California criminal defense attorney before submitting to a polygraph test. You can contact us to review your case details by phone or through the contact form. Eisner Gorin LLP is based in Los Angeles, CA.
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