Polygraph, “lie detector” tests, as they are commonly called, have long been associated with criminal investigations and probation assessments. Their use, however, remains contentious, particularly when it comes to their admissibility in court proceedings. In this post, we will delve into how polygraph examinations work, their potential role in the criminal justice system, the factors that can influence test results, and why polygraph results are generally inadmissible in court.

What is a Polygraph (Lie Detector) Test?

A polygraph examination, or lie detector test, is a process designed to measure and record physiological responses that are believed to be associated with truthfulness or deception. The polygraph test measures several physiological indicators, including:

1. Heart Rate: The number of heartbeats per minute.
2. Respiratory Rate: The pattern of breathing, including rate and depth.
3. Galvanic Skin Response: The electrical conductance of the skin, which can change due to sweating.

These physiological responses are monitored while the individual is asked a series of questions. The underlying assumption is that deceptive answers trigger a physiological response, such as increased heart rate or changes in breathing patterns, although this is not always reliable.

How Modern Polygraph (Lie Detector) Tests Work

Modern polygraph examinations typically follow a standardized procedure. The process usually begins with a pre-test interview, during which the examiner explains the procedure, discusses the individuals medical history, and ensures that the individual understands the test. The questions are also reviewed at this stage, and the individual is given an opportunity to ask questions about the procedure.

Next, the examiner attaches sensors to the individual’s body to monitor the physiological responses mentioned earlier. These sensors are connected to a computer system that records and analyzes the data during the test. The individual is then asked a series of neutral and relevant questions. Neutral questions establish what normal physiological responses look like and often include personal queries, such as “What is your name?” or “Where do you live?”

Once the baseline readings are taken, the subject is then asked the relevant questions related to the matter at hand. These may include questions such as whether they committed a particular crime or violated probation conditions.

The examiner analyzes the recorded data to look for physiological changes that may indicate deception. Results from a lie detector test can be classified as a “truthful” response, a “deceptive” response, or an “inconclusive” response, depending on the analysis results.

Polygraph (Lie Detector) Tests in the Criminal Justice System

Polygraph examinations are sometimes used in criminal investigations and the evaluation of probationers. They are typically offered as a tool to assess the truthfulness of a person involved in a criminal matter, whether as a defendant, suspect, or witness. The results may be used to guide further investigations or as a part of ongoing monitoring in cases involving probation.

Use of Polygraph (Lie Detector) Tests in Criminal Defense and Investigations

In criminal investigations, a defendant may be offered a polygraph test by law enforcement officers to determine their truthfulness regarding specific events related to the case. While the test may provide insight into the defendant’s honesty or guilt, it cannot, by itself, definitively establish the facts of the case. The decision to take a polygraph test is often voluntary, but it is important to note that the polygraph results are not always seen as conclusive proof of innocence or guilt.

Defense attorneys may sometimes advise their clients to take a polygraph test if they believe it will demonstrate their client’s honesty. In some cases, the results of the lie detector test may even be used in plea negotiations or as part of a strategy to avoid trials.

Use of Polygraph (Lie Detector) Tests With Probationers

Polygraph tests are also used as part of probationary assessments. For example, individuals on probation may be required to undergo polygraph examinations to ensure compliance with probation conditions such as abstaining from drug use or staying away from certain individuals. The test may be used to monitor whether probationers are being truthful about their activities and behaviors.

In some cases, a polygraph test may be a condition of parole, especially for those convicted of crimes such as sexual offenses. The polygraph can also help probation officers assess whether a probationer is being truthful about their activities, associations, or adherence to treatment plans. However, like in criminal investigations, polygraph results alone are typically not sufficient to trigger a significant legal consequence.

Anyone participating in a polygraph examination while on probation should be aware that answering certain questions could place them in jeopardy of revocation or being charged with new crimes. The probationer must be ready to assert their 5th Amendment right to any question which could place them in such jeopardy.

Factors That Can Alter Polygraph (Lie Detector) Test Results

While polygraph tests are often assumed to be infallible indicators of truthfulness, several factors can influence the accuracy of the results. These factors can either lead to false positives (indicating deception when the person is being truthful) or false negatives, (failing to detect deception). Here are some factors which can impact polygraph test results:

1. Physiological Conditions: Various physical conditions, such as anxiety, stress, fatigue, or medical conditions like heart disease, can alter physiological responses potentially skewing results. A person might exhibit signs of stress or anxiety even if they are telling the truth, resulting in a false positive.
2. Physiological Factors: The individuals physiological state can also impact the results. A person who is nervous, fearful, or under pressure may show signs of deception even if they are being truthful. Conversely, someone who is calm and self-controlled may mask any physiological responses to deception, leading to a false negative.
3. Countermeasures: Individuals attempting to influence the results of a polygraph examination engage in what are known as “countermeasures.” These tactics include things like controlled breathing or muscle contractions to mask physiological responses. Although examiners are trained to detect such behaviors, it’s still possible for these countermeasures to affect the accuracy of the test.
4. Examiner Bias and Technique: The skill and experience of the examiner can play a significant role in the accuracy of the results. A biased or untrained examiner may misinterpret physiological data, leading to inaccurate conclusions. The procedures used in administering the test can also vary, and inconsistencies in technique can influence the outcome.
5. Type of Questions Asked: The phrasing of questions is crucial to the polygraph process. If questions are poorly structured, overly vague, or misleading, they may trigger inappropriate physiological responses. This can result in a test that is inconclusive or inaccurate.

Are Polygraph (Lie Detector) Tests Admissible in Court?

Despite the widespread use of polygraph examinations in the criminal justice system, their results are generally not admissible in court. The primary reason for this is that polygraph examinations have not been scientifically validated to reliably detect deception. Courts and legal authorities generally consider polygraph results to be unreliable and prone to error, making them unsuitable as evidence in a trial.

Case Law Prohibiting Polygraph Test Results

Several landmark cases have addressed the issue of polygraph admissibility, reinforcing the legal consensus that polygraph results should not be admissible in court:

1. Frye v. United States, 293 F. 1013 (1923): One of the earliest and most significant cases regarding the admissibility of scientific evidence, Frye established the “Frye Standard,” which required scientific evidence to be generally accepted by the scientific community to be admissible in court. Polygraph tests, according to the Frye decision, had not achieved sufficient acceptance in the scientific community to be admitted as evidence. While the Frye Standard has been superseded by other standards in some jurisdictions, it set the foundation for questioning the admissibility of polygraph results in legal proceedings.
2. United States v. Scheffer, 118 S.Ct. 1261 (1998): In this case, the U.S. Supreme Court ruled that polygraph test results are not admissible in court under the Federal Rules of Evidence. The Court concluded that polygraph test results are unreliable and that allowing such results could introduce unfair prejudice or confusion into the trial process. The ruling reinforced the notion that polygraph test results cannot be used as definitive proof of guilt or innocence.

These cases illustrate the legal principle that polygraph results are not sufficiently reliable to be used as evidence in criminal trials, due to their inherent limitations and the potential for error.

Case Law Permitting Polygraph Test Results

To our knowledge, New Mexico is the only state in which polygraph evidence is admissible without significant restriction in criminal trials, even absent a stipulation between the parties. See: Lee v. Martinez, 136 N.M. 166 (2004).

Legal Exceptions and Limited Use of Polygraph (Lie Detector) Test Results

There are exceptions to this general rule. In some jurisdictions, lie detector test results may be admissible under certain circumstances, such as when both parties agree to their inclusion or when the results are presented in a limited capacity, such as to challenge witness credibility. However, this is the exception rather than the norm.

Case law indicates several states require a stipulation as a precondition to the admission of polygraph test results. However, a majority of states either ban polygraph evidence per se, or have not yet addressed this issue. See: State v. A.O., 198 N.J. 69 (2009).

My Final Thoughts

Polygraph (lie detector) test results continue to be a widely used tool in criminal investigations, probation monitoring, and even pre-employment screenings. However, their limitations in accurately detecting deception, along with the potential for influencing factors, mean that polygraph results are generally not admissible as evidence in court. This is supported by case law, which has almost consistently ruled that polygraphs do not meet the standards of scientific reliability required for court proceedings.

For individuals involved in criminal investigations or probation assessments, polygraph examinations can provide valuable insights, but they should not be relied upon definitive proof of truthfulness or deception. As technology and understanding of human behavior continue to evolve, it is possible that polygraph tests will be refined or replaced by more reliable methods in the future.

If you, or someone you know, will be proceeding to trial, challenging a criminal sentence, pursuing post-conviction relief, or litigating a Civil Rights Section 1983 lawsuit, our books are crucial resources in the pursuit of justice. Purchase your copy today, or on behalf of someone incarcerated.