A private polygraph test is when you hire a polygrapher and voluntarily take a lie detector test in order to demonstrate that you are being truthful about a matter. This is frequently done in criminal cases to exonerate you.
The examiner asks you whether you committed the crime. If you answer no and the test indicates truthfulness, these results can be given to the prosecutor in the hopes of getting the case dismissed. If the polygraph indicates you are being untruthful, then the test and the results are kept secret.
A lie detector test and a polygraph test are the same thing. A polygraph is an electrical device that measures biological changes in people when they answer questions. These changes can indicate when someone is being deceptive.
Studies have shown that lie detector tests are not reliable all of the time. Because of this, test results are not admissible as evidence in a jury trial. This is unless the prosecutor and your defense attorney both agree to have the results admitted.
It might be strategic for you to take a private polygraph in three situations. These are when it is used to:
- try and get a charge dismissed during the pretrial process,
- persuade a prosecutor to agree to have the state conduct a follow-up test, or
- convince you to enter into a plea bargain, or plead no contest.
Note that you can take a private polygraph test even if you are in jail. In this scenario, your attorney would need to:
- obtain a court order for the test, and
- plan with the county jail, or state prison, to have the test taken.
Trained polygraph examiners administer lie detector tests for a fee. The typical cost is between $200 and $2,000.
Our California criminal defense attorneys will discuss the following in this article:
- 1. When is a private polygraph a good defense strategy?
- 2. If I fail the test, will the results go to the authorities?
- 3. If I pass the test, can that be used as evidence in court?
- 4. What if I am in jail?
- 5. Do I have the right to present lie detector results as exculpatory evidence?
- 6. How does a polygraph test work?
- 7. How much does a private polygraph test cost?
- 8. Can you fail a lie detector test and still be telling the truth?
A private polygraph test is when a private polygraph examiner conducts a lie detector test.
1. When is a private polygraph a good defense strategy?
A private polygraph test is a good defense strategy in three situations. These are when it is used to:
- convince the prosecutor to dismiss a charge,
- convince the state to conduct a follow-up polygraph of its own, or
- convince you to enter into a plea bargain.
1.1. Dismissal of charges
This strategy requires that you take a private polygraph test early in a case. Often, it gets taken during the pretrial process or even before charges are filed.
If the test results indicate you are telling the truth about not committing a crime, then:
- your defense lawyer may approach the prosecutor, and
- reveal the test results to demonstrate you are factually innocent.
Here, the prosecutor may find the results compelling and agree to dismiss any charges in the case. Prosecutors generally do not want to pursue charges against you if they have reason to believe you are factually innocent.
If there is no dismissal, the prosecutor may decide to reduce a charge to a lesser offense.
1.2. Persuade a prosecutor
There are times when:
- a private polygraph shows your possible innocence, but
- the prosecutor ignores the results and presses on with the case.
In this situation, it is an effective strategy for your defense attorney to:
- approach the prosecutor again, and
- offer to have you take a second polygraph, given by the prosecutor’s office.
The prosecutors may have more confidence in their own polygrapher. If the state’s polygraphers agree that you are being truthful, the prosecutor is more likely to defer to the tests and dismiss the case. 1
1.3. Plea bargain
There are times when:
- you take a private polygraph test, and
- the results imply that you committed the crime in question.
In this event, you may want to think about entering into a plea bargain. This means to plead guilty or no contest to the crime charged or to a reduced charge.
This strategy avoids the risk of:
- you going to trial, and
- being found guilty on the greater charges.
2. If I fail the test, will the results go to the authorities?
If you fail a private polygraph test, the results do not have to go to the:
- police, or
- prosecutor.
Your defense attorney can simply never come forward with the fact that a polygraph was ever administered.
This is what makes a private polygraph “private.”
The law says that the results of a polygraph test can only be used as evidence if the prosecution and you agree that this is okay.
3. If I pass the test, can that be used as evidence in court?
The law says that the results of a polygraph test can only be introduced as evidence at trial if:
- the prosecution and you agree,
- to its admissibility.2
The same rules apply to the following pieces of information:
- the opinion of a polygraph examiner,
- the fact that you (or a witness) offered to take a polygraph test,
- the fact that you (or a witness) refused or failed a test, and
- the fact that a party took a polygraph test.3
4. What if I am in jail?
You can take a private polygraph test even if you are in jail.
In this scenario, your attorney would need to:
- obtain a court order for the test, and
- plan with the county jail, or state prison, to have the test taken.
5. Do I have the right to present lie detector results as exculpatory evidence?
You do not have a constitutional right to present lie detector results as exculpatory evidence.4
Note two things:
- exculpatory evidence is evidence that clears you of guilt, and
- the U.S. Constitution says you have a right to present a defense.5
Despite the above, the Supreme Court has ruled that you do not have a constitutional right to introduce lie detector results into evidence.6
This is true even if the findings of the examination suggest you did not commit the crime in question.
The reason for the rule is that this type of evidence is not 100% reliable.
6. How does a polygraph test work?
A polygraph test is normally conducted in a room with only the examiner and you present.
The test typically begins with the examiner asking you questions while you are not connected to the polygraph machine.
The examiner then connects the machine and asks additional questions.
As the questions are answered, the machine records your physiological changes. These include changes to your:
- breathing rate,
- pulse,
- blood pressure, and
- perspiration.
The examiner analyzes these changes as questions get answered. The idea behind these tests is that:
- if you are telling the truth, you will not exhibit changes in the above conditions (for example, pulse), but
- if you are lying, you will show changes.
For example, signs that you are lying may include:
- a change in your breathing rate just before a question and during an answer, or
- a rise in blood pressure as a question gets answered.
Note that a polygraph test does not measure whether you are lying. Rather, it measures the signs that suggest that you are lying.
7. How much does a private polygraph test cost?
Trained polygraph examiners administer lie detector tests for a fee.
The typical cost is between $200 and $2,000.
The specific cost usually increases with the length of the test. This means an all-day test will be on the high end of the cost range.
A typical two-hour exam is generally $200-$800.
8. Can you fail a lie detector test and still be telling the truth?
Absolutely. This is especially true if you are nervous while taking the lie detector test.
The polygraph may indicate you are lying based on changes in your breathing, blood pressure, etc. Though in reality, these changes could have everything to do with your anxiety.
Legal References:
- See, for example, People v. Reeder (1976), 65 Cal.App.3d 235.
- Evidence Code 351.1 – Polygraph examinations. See also California Polygraph Law.
- See same.
- United States v. Scheffer (1998), 523 US 303.
- See Sixth Amendment to the U.S. Constitution.
- United States v. Scheffer (1998), 523 US 303.