First, how do they work?
To call a polygraph a “lie detector” is slightly misleading.
Polygraphs do not actually detect lies; they detect physiological symptoms of lying, such as sweating, an increased heart rate, heavier breathing, and an increase in blood pressure. The operator of the polygraph observes these physiological symptoms, or a lack thereof, to determine whether or not the subject is lying.
What Is the Primary Issue Regarding Polygraph Tests?
The primary issue with polygraphs is that they rely on the mistaken assumption that lying results in an observable physical reaction. This is not always true. A person might sweat, breathe heavily, or have an increased heart rate because they are nervous or because they are uncomfortable with the question being asked. In other words, someone can be perfectly honest while showing the physical signs associated with lying, and, conversely, someone may be lying while showing none of the associated physical signs.
Polygraphs and Their Role in Canadian Criminal Law
Polygraphs have little to no place in Canadian criminal law. In R. v. Béland, the Supreme Court of Canada decided that polygraph results cannot be introduced as evidence in criminal trials for the following reasons:
1. The Inclusion of Polygraph Evidence Would Oppose the Established Rules of Evidence
The rule against oath-helping is one established rule of evidence that the use of polygraph evidence would violate. This rule prohibits the introduction of evidence for the sole purpose of bolstering one’s credibility. Since the inclusion of polygraph evidence has no purpose other than strengthening the credibility of the witnesses or the accused, its admission would offend the rule against oath-helping.
Similarly, polygraph evidence would breach the rule against character evidence on the basis that evidence cannot be introduced for the sole purpose of suggesting one has good character based on specific acts. The fact that the accused did not lie during the polygraph test cannot be used to suggest that they are not lying in court.
Additionally, the admission of polygraph evidence would violate the rule regarding expert evidence. This rule states that an expert may only share their findings if it will help a judge or jury understand a concept with which they are not familiar. Since judges and juries are already able to decide whether a witness is credible or not, a polygraph operator’s expert opinion on whether a witness is credible is unnecessary.
2. The Inclusion of Polygraph Evidence Would Serve No Purpose That Is Not Already Served by the Judicial Process
The judicial system already has a long-standing process to determine guilt or innocence. It is the duty of judges and juries to evaluate the truthfulness of witnesses, and the admission of polygraph evidence is unnecessary; it risks usurping the role of the judge and jury.
The admission of polygraph evidence may also raise questions about how the polygraph test was conducted, or regarding the credibility of the polygraph operator, inviting digressions from the fundamental issue of the accused’s guilt.
Contact Filkow Law if You Need Clarification or Help with a Legal Issue
Our criminal defence lawyers understand this frequently discussed topic and are more than happy to help clarify any questions you may have.
If you have other legal concerns or issues, contact Filkow Law. It is best to get help as early as possible, and our experienced team offers knowledgeable, confidential, and results-driven legal representation to help you achieve the best possible outcome.
