Private Polygraph Tests in California Criminal Cases

If you watch cop shows on TV, you probably know what a polygraph test is. Otherwise known as a "lie detector test," a polygraph is an electrical device that measures biological changes in people when they answer questions. In theory, these biological changes can show whether the person is lying or not....

...but only in theory. Polygraph tests are not the foolproof lie detectors the media may make them out to be. Experts disagree about how accurate they actually are at determining when someone is telling the truth. Because of this, they can no longer be admitted as evidence in California criminal jury trials unless both the prosecution and the defense agree. 1

But that doesn't mean these lie detector tests have no value. While polygraph tests can't always tell us if someone is lying, they can do so in a number of cases-possibly in the majority of cases. This is why some employers still request that employees or job applicants take them 2...and why high-profile people like politicians accused of misconduct are often pressured to take them.  3

Because of this, polygraph tests can still be a useful tool for asserting
legal defenses and fighting criminal charges in California. Private polygraph examiners can administer a polygraph test to a criminal defendant. If the test shows that s/he is telling the truth, then these results can be used to persuade the prosecutor to drop charges. If the results suggest the accused is being deceptive, the defense can simply never come forward with the fact that a polygraph was administered at all.

But the lie detector results may not be admitted into evidence at the California criminal trial, unless both the prosecutor and the defendant agree to let them be admitted.  4

In this article, our experienced California criminal defense attorneys5 explain how private polygraphs may be used in California criminal cases by addressing the following:

1. Introduction to polygraph (lie detector) tests
2. Polygraph test results in California
criminal cases
3. How to use private polygraphs in California
criminal cases

3.1. What is a private polygraph test?

3.2. Dismissal of charges

3.3. Admission of polygraph evidence at trial

If you would like more information after reading this article, we invite you to contact us at Shouse Law Group.

1. Introduction to polygraph (lie detector) tests

A machine that can tell you if someone is lying sounds like something out of science fiction. But in fact a polygraph is exactly that...at least some of the time.

A polygraph is an electrical device that measures changes in a person's blood pressure, pulse, breathing, and perspiration (sweating).  6 The idea is that stress affects all of these things and that there is a biological reaction when people do something stressful like telling a lie. The polygraph machine can measure that biological reaction.

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The polygraph is attached to the person being tested. The person giving the test-also known as the "polygraph examiner"-then asks them a set of questions. If the person being tested shows physical signs of stress when answering questions about the crime, then it may be the case that they are lying.

Example: Isaac and Gary are both accused of participating in a large-scale bank robbery. Both claim that they were somewhere else on the day of the robbery. Both Isaac and Gary receive polygraph tests.

When Isaac is asked where he was on the day of the robbery, his pulse, blood pressure, etc. all stay normal. This probably means that Isaac is telling the truth and is innocent.

But when Gary is asked where he was, his pulse races, his blood pressure goes up, and he starts to sweat. This may mean that Gary is lying in response to this question and is guilty.

But in fact people's biological reaction to the experience of lying is probably more complicated than this. Scientific studies have shown that polygraph machines are not reliable all of the time.7

The question of how reliable they are doesn't really have a good answer. Some studies suggest that polygraph tests correctly determine whether someone is lying more than 90% of the time (that is, they catch more than 9 out of 10 liars). But other studies suggest that they only get it right around 60% of the time...meaning that in 4 out of 10 cases, the results are wrong.  8

According to Riverside criminal defense lawyer Michael Scafiddi:  9

"The problem with polygraph tests is NOT that they don't really tell you if someone is lying. In most cases, they do give accurate results. The problem is that a lot of people who sit on juries may think that they're foolproof and work all the time, which they definitely do not. So polygraph tests can be a dangerous tool in criminal trials."
2. Polygraph test results in California criminal cases

Juries may think lie detector tests are always accurate even though they're not. Because of this problem, the state of California now strictly limits the use of polygraph results in criminal jury trials.

In California, the results of a polygraph test can no longer be presented as evidence in a criminal case...unless both the prosecution and the defense agree that it's okay.  10 The same goes for the following pieces of information:

  1. The opinion of a polygraph examiner,
  2. The fact that someone (like the defendant or a witness) offered to take a polygraph test,
  3. The fact that someone refused or failed to take a polygraph test, and
  4. The fact that someone took a polygraph test.  11

If you are accused of a crime, this rule can help you...or hurt you, depending on the circumstances.

Example: Alexander is accused of committing a robbery (which he did not do). He was with his mistress when the robbery took place. Because he is married doesn't want his wife to know this, he comes up with a false alibi as a legal defense.

The police make Alexander take a lie detector test when he is booked for the crime. The results indicate that he is lying about his alibi (which he is, but not because he committed the robbery). Luckily for Alexander, the prosecution cannot present these results to a jury unless Alexander and his lawyer agree.

BUT...

Example: Alexander is accused of committing a robbery (which he did not do). The prosecution has a key witness, Wilma, who claims she witnessed the robbery and identifies Alexander as the robber in a pretrial lineup. Wilma has a background of being unstable and unreliable.

Alexander's lawyer, Larry, suspects Wilma is lying. Larry asks her to take a private polygraph test (we'll describe these in more detail below). She refuses. Larry cannot tell the jury at trial that Wilma was asked to take a polygraph test and refused (unless the prosecutor agrees to let this information in). Of course the prosecutor probably won't agree, since this information would hurt their case.

But, as we noted above, the results of a polygraph test are admissible at trial if both parties agree to let them in.  12 Let's change our example one more time:

Example: Alexander's lawyer, Larry, suspects that Wilma, the prosecution's star witness, is lying. The prosecutor thinks Wilma is probably telling the truth.

So the two lawyers agree that Wilma will take a private polygraph test. Before she takes the test, they also sign an agreement saying that the results will be admitted into evidence at the trial and presented to the jury.

The test results end up indicating that Wilma is probably lying. Because the prosecution agreed, Larry and Alexander present the results at the jury trial...and Alexander is found not guilty.

Prosecution has to disclose results

One other important thing to know about polygraph tests is this: the prosecution is required to tell a criminal defendant about any polygraph results that suggest a witness for the prosecution is lying.  13 This doesn't mean that those results can be admitted at trial if the prosecution doesn't agree to admit them...but they do mean that the defendant will be able to use that information to build their case.

Example: Let's say the prosecutor in Alexander's trial starts to think his star witness Wilma may be lying about where she was on the night of the robbery. He administers a polygraph test...and the results suggest that Wilma is lying. The prosecutor has to tell Alexander and his lawyer Larry about this.

Alexander and Larry can't tell the jury at trial about these results. But this does clue them in to the possibility that Wilma is lying. Larry investigates this further and ends up finding evidence that Wilma has been convicted of perjury (lying under oath) in the past. He can introduce this evidence at trial.
3. How to use private polygraphs in California
criminal cases

3.1. What is a private polygraph test?

The above examples show that it can sometimes be useful for a criminal defendant to take, or have someone else take, a polygraph test...even if the results won't necessarily be admissible in court. The results of a polygraph test can help support a variety of common legal defenses to California crimes.

Because of this, criminal defendants and their lawyers often decide to arrange for a polygraph exam with a California private polygraph examiner. These are trained polygraph examiners who will give a lie detector test for a fee. The tests usually take two (2) to two-and-a-half (2.5) hours. The cost usually starts at five hundred ($500) to one thousand ($1000) dollars.

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Let's say you have been falsely accused of a crime and your lawyer suggests you take a private polygraph test. There are several ways you may be able to use the results:

3.2. Dismissal of charges

You can take a private polygraph during the pretrial process of your case.

If the results indicate that you're telling the truth about not having committed the crime, then your lawyer may approach the prosecutor and tell him/her about the results. Even if you can't present these polygraph results in court, the results will suggest to the prosecutor that you really didn't do it...and thus that you will probably be able to come up with other evidence that you are innocent (alibis, etc.).

The prosecutor probably knows that polygraph tests are reliable most of the time (if not all of the time) and does not want to waste his or her time building a case to convict an innocent person...especially since this may well mean s/he will lose the case.

The prosecutor will probably want to see the full test results and maybe even a video of the test. But if s/he thinks you are probably innocent after examining these materials...the prosecutor may decide to DISMISS the charges. And with this you're free!

3.3. Admission of polygraph evidence at trial

Unfortunately, things aren't always that simple. Some prosecutors will press ahead with a case even if they see results of a lie detector test indicating that they have the wrong man (or woman).

In these cases, another strategy may be more helpful. It would go something like this:

  1. You (the criminal defendant) take a private polygraph test during the pretrial process. The results show that you are probably not lying when you say that you did not commit the crime...or that some other legal defense probably applies.
  2. Your lawyer approaches the prosecutor and offers to have you take a second polygraph test, this time one given by the prosecutor's office...under one condition. The condition is that the prosecutor has to agree beforehand that the results, whatever they are, will be presented at the trial.
  3. You take the test, and the results show that you are probably innocent. The prosecutor is stuck, since s/he has already agreed to admit the results into evidence. So they are presented to the jury. The jury is then more likely to return a verdict of "innocent."  14
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There are possible variations on this strategy too. For example, the lawyers for the defense and prosecution could also agree that the victim of the crime or certain witnesses will take polygraph tests and that the results will be admissible at trial.

Obviously, though, it wouldn't be a good idea to try this strategy unless you are reasonably confident that the polygraph results will be helpful to you in your case. This is why a private polygraph is such an important tool-it allows a criminal defendant and his/her lawyer to do a "dry run." If the results of the private polygraph suggest the defendant is probably innocent, then it's likely that the results of a polygraph given by the prosecutor's office will too.

If the results of a private polygraph are not good (i.e., if they indicate the defendant is lying and so may be guilty), then that can still be helpful information, for several reasons.

    1. It means that if the prosecutor suggests a polygraph test, it's probably a good idea to refuse. As we discussed above, the fact that you refuse to take a polygraph test can't be told to the jury unless you agree 15...so there's nothing to be lost by refusing.
  1. Depending on the other facts of the case, it may mean that it's worthwhile to enter into a plea bargain...that is, to plead guilty or no contest to a reduced plea and/or a lesser sentence...rather than risk going to trial and being found guilty on greater charges.
Call us for help...
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If you or loved one is in need of help with using a private polygraph as a legal defense and you are looking to hire an attorney for representation, we invite you to contact us at Shouse Law Group. We can provide a free consultation in office or by phone. We have local offices in Los Angeles, the San Fernando Valley, Pasadena, Long Beach, Orange County, Ventura, San Bernardino, Rancho Cucamonga, Riverside, San Diego, Sacramento, Oakland, San Francisco, San Jose and throughout California.

Legal References:

1Evidence Code 351.1 - Polygraph examinations; results, opinion of examiner or reference; exclusion. ("(a) Notwithstanding any other provision of law, the results of a polygraph examination, the opinion of a polygraph examiner, or any reference to an offer to take, failure to take, or taking of a polygraph examination, shall not be admitted into evidence in any criminal proceeding, including pretrial and post conviction motions and hearings, or in any trial or hearing of a juvenile for a criminal offense, whether heard in juvenile or adult court, unless all parties stipulate to the admission of such results.")

2Labor Code 432.2(b) - Polygraph or lie detector test as condition of employment; advice of rights. ("(b) No employer shall request any person to take such a test, or administer such a test, without first advising the person in writing at the time the test is to be administered of the rights guaranteed by this section.")

See also Los Angeles Police Protective League v. City of Los Angeles, (1995) 35 Cal.App.4th 1535, 1540 (holding that a general ban on required polygraph testing as a condition of employment does not prohibit polygraph testing as a condition of a promotion at work).

3 See, e.g., Dan Vergano, "Telling the Truth About Lie Detectors," USA Today, Sept. 9, 2002 (describing calls for U.S. senators to take lie detector tests as part of an investigation into an intelligence leak); "Levy Family Calls for Lie Detector Test for Condit," ABC News, July 9, 2001 (describing how the family of a missing Washington, D.C., intern called for a congressman with whom she may have been romantically involved to take a polygraph test).

4Evidence Code 351.1(a).

5Our California criminal defense and California immigration attorneys have local Los Angeles law offices in Beverly Hills, Burbank, Glendale, Lancaster, Long Beach, Los Angeles, Pasadena, Pomona, Torrance, Van Nuys, West Covina, and Whittier.  We have additional law offices conveniently located throughout the state in Orange County, San Diego, Riverside, San Bernardino, Ventura, San Jose, Oakland, the San Francisco Bay area, Sacramento, and several nearby cities.

61 Witkin Cal. Evidence Ch. VII, § 87. ("The polygraph, popularly known as the lie detector, is an electrical device that, when attached to a person, registers and charts the person's changes in blood pressure and pulse, respiration, and perspiration while under questioning. Its principal use is in criminal investigation.")

7 People v. Reeder, (1976) 65 Cal.App.3d 235, 242. ("At this point it bears repeating that polygraph evidence is considered by the great weight of authority to be so unreliable as to be inadmissible without a stipulation.")

8 Dan Vergano, "Telling the Truth About Lie Detectors," USA Today, Sept. 9, 2002.

9 Riverside criminal defense lawyer Michael Scafiddi is a former police officer and police sergeant. He knows how the police put together criminal cases, including how they make use of polygraph tests and how they react when presented with private polygraph results...which helps him understand how to defend those cases. He represents clients in all San Bernardino County courthouses and Riverside County courthouses.

10 Evidence Code 351.1 - Polygraph examinations; results, opinion of examiner or reference; exclusion. ("(a) Notwithstanding any other provision of law, the results of a polygraph examination, the opinion of a polygraph examiner, or any reference to an offer to take, failure to take, or taking of a polygraph examination, shall not be admitted into evidence in any criminal proceeding, including pretrial and post conviction motions and hearings, or in any trial or hearing of a juvenile for a criminal offense, whether heard in juvenile or adult court, unless all parties stipulate to the admission of such results.")

11 Same.

12 People v. Trujillo, (1977) 67 Cal.App.3d 547, 554. ("It is equally well settled that the results of a polygraph examination [including a private polygraph] may be admitted into evidence at the trial pursuant to a stipulation entered into by both parties.")

13 People v. Price, (1991) 1 Cal.4th 324, 419-20. ("Although the prosecution has a duty to inform the defense of polygraph results that cast doubt on the credibility of a prosecution witness, the existence of this duty does not make the results admissible.")

14 For an example of a case in which this strategy was applied, see People v. Reeder, (1976) 65 Cal.App.3d 235, 238-39. ("Prior to trial, defendant's attorney stipulated in writing with the district attorney that defendant and the victim each be administered a [private polygraph] by a licensed examiner, and that the details and results of the tests together with the opinions of the examiners be received in evidence. The stipulation was signed by defendant and his attorney and by the victim and the prosecutor. Thereafter defendant and the victim submitted to separate polygraph tests administered by different examiners from the California Department of Justice.")

15 Evidence Code 351.1.

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