Polygraph Examination Use in CA Criminal Cases. Reliability, Admissibility, & Criminal Defense Related Issues Regarding Polygraph Exams in California.
- sexcrimesdefensela
- Feb 24
- 9 min read
Updated: Mar 20
As a California sex crimes criminal defense attorney, I am frequently asked about polygraph examination reliability and admissibility as these “polygraph tests” relate to sex crimes allegations, prosecution, and criminal defense.
More specifically, many sex crimes criminal suspects and criminal defendants want more information regarding the following:
1. What is a Polygraph Examination (i.e., “Lie Detector Test”)?
A polygraph examination, often called a “lie detector” test, is a non-invasive process that uses a “polygraph machine” to detect and record the physiological changes of an examinee as those changes relate to questions asked by a polygraph examiner.
The changes in the examinee’s physiology allegedly indicate purposeful misrepresentation in the examinee’s responses to the questions posed due to cognitive dissonance (i.e., mental discomfort from holding two inconsistent beliefs).
2. How Does a Polygraph Machine Work?
A polygraph examination machine works by detecting and recording the changes in an examinee’s physiology, which are reportedly uncontrollable and caused by stress and anxiety related to knowingly deceptive answers to the polygrapher’s questions (i.e., cognitive dissonance).
The physiological changes measured by the polygraph machine include:
Blood Pressure,
Breathing Pattern (Respiration Rate),
Heart Rate,
Changes in Electrical Conductance Related to Sweat Production (Galvanic Skin Response [GSR]).
Eye Movement & Dilation (More Sophisticated Machines)
At the conclusion of the polygraph exam, the polygraph examiner analyzes and interprets the data produced by the polygraph machine to determine if there are significant variations or fluctuations in the examinee’s physiology in response to the questions posed.
The fluctuations in physiology are reportedly the uncontrollable result of anxiety caused by cognitive dissonance, which is turn, is caused by the purposeful misrepresentation known facts.
Note: In criminal cases, polygraph examinations are most used in connection with allegations of child molestation type charges, including Penal Code 288(a) [Lewd Act on a Child Under 14], & 288.5 [Continuous Sexual Abuse of a Child], and PC 287a [Oral Copulation on a Minor].
3. Are Polygraph Examinations Reliable?
The reliability of the polygraph exam is a topic of debate. While polygraph examinations can provide useful information, they are not foolproof, and factors such as the examinee’s emotional state, medical condition, subjective belief of a false “truth,” and even the ability of the examinee to understand the questions, can all affect the reliability of a polygraph examination.
Also, the polygraph examiner’s expertise, training, and subjective bias can influence the results or the interpretation of the results.
In some situations, polygraph examinations have been shown to produce false positives (indicating deception when someone is truthful) and false negatives (not detecting deception when someone is lying).
Note: The fear of the polygraph examination test itself or personal issues, can affect a person’s physiology, and therefore, skew results of the polygraph exam.
4. Should Criminal Suspects Take Polygraph?
When law enforcement is requesting that a criminal suspect take a polygraph examination, the criminal suspect will almost never benefit from complying with this request.
This is because anything the defendant says or does before, during, or even after the examination itself can be used against the criminal suspect, and yet, the results of a polygraph examination will never exonerate the criminal suspect.
This is true even though the results of the polygraph examination cannot be used against the criminal suspect except in very limited circumstances.
For example, David is asked to take a polygraph examination after he is suspected of annoying or molesting his granddaughter. David agrees to take the exam because law enforcement claims that the exam result will exclude him from being a suspect in the case. David takes and “passes” the polygraph exam, but law enforcement continues to pursue David as a criminal suspect because of inconsistent statements he made during the exam, even though exam result themselves cannot be used against David in the criminal case.
A criminal suspect might be asked to take a polygraph examination by his or her criminal defense lawyer. This is a private polygraph examination without law enforcement presence or knowledge.
The purpose of a private polygraph examination for a criminal suspect is determined, in advance, if the criminal suspect (or criminal defendant), would likely pass a polygraph examination if conducted by law enforcement. This could be beneficial to the criminal suspect in some limited situations.
Typically, the only words a criminal suspect, or even a probationer or parolee, should make in response to a sex crimes allegation is that he or she does not want to make any statement, and that he or she would like to have his or her lawyer present during any questioning regarding any subject.
5. Can Polygraph Results Incriminate Me?
Polygraph results are not admissible in California courts due to their controversial reliability. There is an exception to the admissibility of polygraph examination results if all parties agree (i.e., district attorney and criminal defendant).
This rule against the use of polygraph exam results against the criminal defendant is absolute and makes no exception other than by agreement between the defendant and the district attorney (Penal Code 351).
In fact, clear evidence that proves a defendant submitted to a polygraph examination may not be used as impeachment against the defendant even if the defendant clearly lied about taking the test.
In addition, without an agreement between the defendant and the district attorney, none of the following evidence is admissible in criminal court:
Evidence that the defendant offered to take a polygraph examination
Evidence that the defendant refused or failed to take a polygraph examination
Evidence that the defendant submitted to a polygraph examination
The results of a polygraph examination, and
The opinion of the polygrapher
Note: A criminal defendant cannot be forced by anyone to take a polygraph examination. This does not mean that failure to take a polygraph examination is a good option, especially for probationers or parolees who have agreed to submit to polygraph examinations as part of their respective probation or parole conditions.
It is important to understand that polygraph testing may be a valid condition of probation, but the court should impose restrictions on the questions (Brown v. superior Court (2002) 100 CA4th 313).
Also, a person who is obligated to take a polygraph examination as a condition of probation or parole is probably protected from having the results of that polygraph used as evidence against him or her.
This is because the probationer or parolee’s statement is compelled in this situation and would not stand against a Miranda Violation Defense.
6. Should I Refuse to Take a Polygraph Test?
Whether a criminal suspect should refuse to take a polygraph examination depends on the circumstances of the case and who is asking for the examination (i.e., law enforcement v. criminal suspect’s lawyer, etc.).
With that said, the general rule is that a criminal suspect (or criminal defendant) should neither refuse, nor agree to take a polygraph examination by law enforcement.
The best practice in most circumstances is for the criminal suspect to inform law enforcement that he does not wish to answer any questions, and that he would like his or her lawyer to be present during any questioning.
The criminal suspect should thereafter contact a criminal defense attorney without delay to ascertain the best way to handle any polygraph examination in the future, if at all.
7. Can a Polygraph Prove My Innocence?
Polygraph examination results will never prove a criminal suspect’s innocence because the result of a polygraph examination cannot be used in court without prior agreement.
Nevertheless, sometimes polygraph examinations are used to “exclude” a suspect, at least unofficially, and at least for a while.
8. Can I Fool or Trick a Polygraph?
Some people claim to be able to fool or trick a polygraph exam by controlling their physiology in response to questions. Some methods people use to trick or fool their physiology in response to questions (which results in fooling or tricking the polygraph machine) include:
Irregular Breathing: Some people can regulate their breathing pattern to minimize the tiny, almost undetectable, fluctuations in respiration rates between breaths.
Physical Discomfort: Purposeful physical discomfort or pain during questioning, like biting the tongue or putting pressure on an undisclosed injury, has been used to produce consistent physiological responses throughout the polygraph questioning, which could result in no detectable changes in the examinee’s physiology during questioning.
Stress Management: Relaxation techniques and mental strategies designed redirect perceived questions is claimed to help control a person’s physiological responses during a polygraph examination.
Emotional Control: Masking anxiety through medication or emotional control, similar to method acting, is claimed to impact the physiological responses of an examinee during a polygraph examination.
Pre-Test Preparation: Knowledge about the polygraph process and common questions might allow individuals to better prepare and respond in ways that could potentially confuse the results.
Note: Skilled polygraph examiners are trained to recognize patterns and anomalies that might indicate an attempt to manipulate the results. They look for inconsistencies and physiological responses that are out of the ordinary.
Example: David is asked by law enforcement to take a polygraph examination after he is accused of oral copulation of his intoxicated girlfriend (i.e., “date rape”). David agrees to the request, but before he takes the test, he puts a small rock in his shoe. During questioning, David puts pressure on the rock to cause discomfort and manipulate his physiology during questioning.
Keep in mind that polygraphs measure multiple physiological responses, and the interplay between them can be complex.
Attempting to control or manipulate one response may not necessarily affect all relevant indicators in a predictable manner.
Also, attempting to trick a polygraph test raises ethical concerns and can have legal or professional repercussions for a criminal suspect and/or his or her criminal defense lawyer. It is generally advisable to decline a polygraph examination through the criminal suspect’s sex crimes criminal defense lawyer.
However, if the criminal suspect is going to take the polygraph examination over his or her criminal defense lawyers’ advice, then he or she should approach the tests with honesty and integrity rather than attempting to deceive them.
9. My Rights Regarding Polygraph Exams?
A criminal suspect, or criminal defendant does not have to take a polygraph examination upon request from any law enforcement agency.
In other words, the criminal suspect or criminal defendant usually has the right to refuse to take a polygraph examination. However, refusal to take the polygraph examination should be made through the criminal suspect’s criminal defense lawyer.
If the criminal suspect wants to take a polygraph over the advice of his criminal defense attorney, or when the suspect must take a polygraph (See VOP issues below), then the polygraph examination should only be performed under conditions approved by the sex crimes criminal defense lawyer (See Probation or Parole Exceptions Below).
10. Post-Conviction Use of Polygraph Info:
A person who is on probation or parole is sometimes obligated to submit to a polygraph examination as a condition of his or her probation or parole.
This is rare as most probation or parole terms do not have the probationer or parolee waive his or her Fifth Amendment Right to Remain Silent in the fact of a new criminal allegation, but it does occur, especially in cases related to a conviction for lewd and lascivious act on a child under fourteen cases (PC 288(a)), and other sex crimes convictions related to children.
If the probationer or parolee is subject to a condition that requires him or her to take a polygraph examination as part of his or her probation or parole, the probationer or parolee should seek the advice of a criminal defense attorney before taking the required polygraph examination so that any criminal liability can be avoided related to crimes for which the defendant was not convicted.
Also, according to Penal Code 351, the results of a polygraph examination cannot be used against the defendant. So why would a court have this condition included as a term of probation or parole in the first place?
The answer is that anything the probationer or parolee says before or during the questioning can be used against him, even if the results of that exam cannot be used against him.
11. PC 288 Crimes & Polygraph Exams
In practice, polygraph examinations in criminal law are most used in connection with sex crimes, such as child molestation cases, especially in “he said/she said” child molestation cases, where the defendant’s confession is the best evidence of the defendant’s guilt.
This is true even when the results of the polygraph examination themselves cannot be used as evidence against the defendant per California law.
For example: Eric is accused and suspected of committing sexual penetration by object with force (PC 289). Eric is asked by law enforcement to take a polygraph exam to “clear his name.” Eric takes the polygraph exam. Afterwards, law enforcement tells Eric that he ‘failed the polygraph.’ (Regardless of whether Eric in fact failed the polygraph exam).
Thereafter, Eric confesses to the crime to law enforcement because Eric feels that a confession will now best serve to reduce his criminal liability (since he “failed” the polygraph examination according to police).
Result: The results of the polygraph exam are not admissible, but Eric’s confession after the polygraph exam is probably admissible if law enforcement properly followed Miranda Warnings and Waivers. (Most polygraph examinations are preceded by Miranda Warnings and Waivers).
To learn more about polygraph examinations used in sex crimes cases, or issues related to PC 351, contact our sex criminal defense lawyers without delay.
Our team of experienced criminal defense lawyers have successfully handled hundreds of felony and misdemeanor criminal cases in San Bernardino, Riverside, Orange, and Los Angeles County.
We have experience with cases involving polygraph examinations and we offer free in-office first-time consultations for criminal suspects and defendants every day of the week. Call today!
909-913-3138
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