Everyone has heard of lie detectors being used by police or prosecutors, but are lie detector tests even admissible in court in California? As it turns out, the California polygraph law about evidence admissibility makes it very unlikely that a lie detector will be admitted in court, but police still ask defendants to take them even if they can’t be used as evidence.
About Polygraph Tests
Polygraphs, commonly known as lie detector tests, measure changes in a person’s heart rate, breathing patterns, blood pressure and sweat levels to determine whether or not that person is telling the truth. In theory, a person’s body will demonstrate signs of stress when she lies and these are the physical attributes a lie detector tests for.
In practice, a person may fail a lie detector test because he is stressed for any number of reasons unrelated to lying. Alternatively, some people can pass polygraphs while telling nothing but lies because they are able to maintain their composure no matter what questions have been asked. For these reasons, polygraphs are accurate only somewhere between 60 and 90% of the time depending on what study you look at.
Are Lie Detector Tests Admissible in Court in California?
Even at 90% accuracy, that still means polygraphs are inaccurate one out of ten times, which is not an acceptable margin of error when it comes to a person’s guilt or innocence in court. That is why the California polygraph law limits their use in court. In fact, these tests can only be admitted to court if both the prosecutor and the defense lawyer agree it is ok for the test to be used as evidence.
Although the California polygraph about the test’s admissibility in evidence law allows for lie detector results to be admitted with both parties consent, it is very rare for this to occur. A defendant wouldn’t want a negative report introduced and a prosecutor wouldn’t want a positive report admitted. Realistically, prosecutors are very skeptical of defense-administered lie detector tests because they both question the impartiality of the examiner and the reliability of the results.
The California polygraph law says if the two sides do not agree to admitting a polygraph test into evidence, then the opinion of a polygraph examiner, the fact that someone did take a polygraph test, the fact that someone offered to take a lie detector test, or the fact that someone refused to take such a test cannot be admitted into evidence either.
So Why do Police Ask Defendants to Take Polygraphs?
Lie detectors are most commonly used in criminal investigations to allow a detective to get a suspect to confess after taking a real or even sometimes a fake test -in these cases, investigators don’t care about the California polygraph law regarding admissibility of this evidence stopping these from being admitted in court, because they have no intention of using the results in court, they just want to get the suspect talking. This is another reason to always have your defense attorney present while speaking with police, as he will advise you about the California polygraph law.
The Prosecutions’s Responsibility
The defendant isn’t the only one who may be given a polygraph test. In some cases, witnesses may also be asked to take a lie detector test. If a witness for the prosecution was given the test without the defense attorney giving prior approval that the results can be used in court, the District Attorney must tell the defense if the witness failed the test. At this point, neither the DA or the defense will be able to use this information in court, but both sides may be able to use this information to strengthen their case.
If you have any questions about the specifics of California polygraph law regarding admissibility, please call (760) 643-4050 to schedule a free initial consultation with criminal lawyer Peter M. Liss.
