If police ask to participate in a polygraph (or “lie-detector”) test, should someone do it?

Disclaimer (a must read): 

This article is for informational and academic purposes only.  This article cannot, and should not, replace proper legal advice by a properly qualified lawyer.  If you are under investigation or suspicion, it is essential you speak to a lawyer immediately to obtain proper legal advice as it relates to your own predicament.  This article is written as it relates on to Canadian law, and more specifically criminal justice in Ontario.  Other countries and jurisdictions treat polygraphs differently and refusal to participate in them may have negative and severe consequences.  The information provided in this article may be completely inapplicable to laws outside Canada.  Speak to an lawyer/attorney in your specific jurisdiction if you have questions, and particularly so if you are under investigation or arrest.

“That a lie which is all a lie may be met and fought with outright, but a lie which is part a truth is a harder matter to fight.” – Alfred, Lord Tennyson

In the course of our practice, it is common for individuals under investigation to ask whether they ought to participate in a police lie detector test.  Although every situation is different, the answer to 99.9% of inquiries is “no, absolutely not.”  From there, we  provide clients with specific legal advice on how to properly respond to the police request so as not to harm their interests or expose themselves to unnecessary risk.  Although there may be circumstances where it’s in the individual’s interest to participate, those occasions are extremely rare, unique, and nuanced.

When a person is under investigation, it is critical for that person to obtain proper legal advice from a lawyer who specializes in criminal law immediately and before there is any agreement or refusal to participate in a polygraph examination.  Failure to do so could have lasting, severe, and irreparable consequences that are explained further below.  The importance of obtaining specific legal advice from a properly qualified  lawyer at this stage cannot be stressed enough.  If police have reached the stage of requesting a polygraph test, they are treating it seriously; any person requested to participate ought to as well.

lie detector test polygraph

This area of law is extremely complicated, nuanced, and fact sensitive.  Therefore, only those lawyers who are highly specialized and practice exclusively in criminal law ought to provide advice on these matters after knowing the full circumstances.  To emphasize once more, this article cannot replace proper legal advice and is meant to provide some basic principles of law and academic commentary and perspective.

What is a polygraph or lie detector test, and why do police request them?

Cooperate with police lie detector

A “polygraph examination” is more commonly known as a “lie detector” test.  Requests by police to participate in such examinations can come at any time.  Request to participate are most frequent at the beginning of an investigation when police are  trying to obtain evidence and develop a theory of the case.  A criminal charge is not required for police to make such a request.  For that matter, police are not required to even consider that person a “suspect”.

However, it would be counterintuitive and rare that police would waste their time and expense on obtaining polygraphs from people they are not interested in.   Put it this way, if police felt a person was telling the truth, why would they need a lie detector?  As a matter of common sense, would you ask someone to participate in a lie detector test if you believed them?

Therefore, when people are requested to participate in such examinations, they are almost always suspects or “persons of interest” – even if the police insist they are not.  When police say a person is not a “suspect” it may be just another way of saying there is not enough evidence to consider them as one. However, once a person complete a polygraph test that may all change – indeed, that is probably the point.  It is very common for police to lack the grounds to arrest someone until after someone has completed a polygraph examination, even in instances where a person “passes” the test or vehemently denies their guilt.

If a person is innocent, there is no obligation to prove it to police.

Often times, people who see themselves as innocent feel they should participate to quickly clear their name.  It’s human nature to want people, and police, to believe they did not do anything wrong.  This human desire towards exoneration does not serve the person/suspect well under police investigation.

If one knows they are innocent, that should be enough for peace of mind.  Trying to convince police to reverse their suspicions exposes oneself to considerable risk with little, to any benefit.  As indicated below, even if a person “passes” a polygraph examination, that result isn’t admissible in court to prove innocence anyway.   Further “passing” a lie detector test is not conclusive to police and the investigation will continue as they see fit – except now police have a statement that may become relevant to impeach credibility at a later date.

If you’re guilty…well do we need to say more?

In addition to the reasons set out in this paper, it should be obvious to any person who is guilty of a crime that it is not in their interest to participate in a lie detector test.  This is the same whether a person is guilty to the full extent to which the police are alleging, or even if the person feels they are only partially guilty.  A person seeking to set the record straight on their degrees of guilt is rarely favourable to their interests, and rarely changes the police view on how guilty that person is.  Invariably, this type of approach just serves to dig a person deeper and deeper into legal problems and lies.

If you pass or fail, the results are not admissible in court.

From a legal standpoint, particularly if a person is s suspect, there is simply nothing to be gained by agreeing to a polygraph examination and a person takes enormous risks in engaging in such a process, regardless of actual guilt or innocence.

As found by the court in R v Beland[1987] 2 SCR 398, polygraph results are inadmissible in court because such admission would violate many rules of evidence, namely, the rule against oath helping, the rule prohibiting the admission of prior-consistent statements and the rule against bolstering character. Furthermore, the polygraph is not recognized as proper expert evidence.  The conclusion of the polygraph examiner is also inadmissible as it goes to the very heart of what the role of the judge or jury is – to determine what the truth is or where doubt may lie.

A statement is a statement, is a statement.  Polygraphs examinations are statements like any other.

polygraph examination

A suspect is never obligated to give any statement to the police, even upon arrest.  In almost all instances, lawyers will advise a person not to make a statement to police if they are under investigation for myriad reasons.  Since a polygraph examination requires questions and answers, it too is a statement and the same principles against self-incrimination apply.

People who seek to exonerate themselves through their exculpatory statements will invariably provide facts and omissions that may later serve to impeach their own credibility. This is because the more people talk the more likely it is for these facts and omissions will appear exaggerated, incorrect, misstated, or unreliable to police.  Those inevitable shortcomings will then be exploited under cross-examination at trial.   Even people who seek to tell nothing but the truth can look incredible under a skilled cross-examination.  Offering any sort of statement provides the examiner the means to craft skillful impeachments and cross-reference every fact to hard evidence that may contradict a person’s version of events.

Fortunately, under Canadian law, silence, or refusal to participate in a police investigation is not admissible to prove a person’s guilt.  Silence is not evidence and it cannot be cross-examined upon – it’s as simple as that.

Polygraphs are limited in their reliability:

The reliability of polygraph testing is of considerable debate and controversy that is far too in depth to explore in this short article.  Suffice to say that the science is not perfect (or we would not have a need for courts and trials).  The inherent unreliability in this sort of testing simply means that passing means very little to police and is not in any way determinative in police believing in a person’s innocence.  On the other hand, failure often adds to suspicions and conclusions of guilt of the investigators.

A vast collection of articles on polygraph reliability and lack thereof can be found by a simple Google Scholar search. 

So why are polygraphs / lie detector tests still used under Canadian law if the results are not admissible?

Regardless of their admissibility, polygraphs still serve as very useful investigative tool for police. When a suspect is confronted with failed polygraph results, they often offer a confession.

In fact, the Supreme Court of Canada ruled in R v Oickle, [2000] 2 SCR 3, that police can use polygraph results to deceive a suspect in order to elicit a voluntary confession, provided the level of deception is not such that it would shock the community.  Upon obtaining a confession Police have reasonable and probable grounds to arrest you, however a successful test will not stop police from using evidence they already have against you or from taking steps to obtain further evidence in order to justify your arrest.

Conclusion on why you should NOT participate in a lie detector test / polygraph test if asked by police:

In short, the reasons as to why it is generally not in the interest of any person to engage in a polygraph test are as follows:

  • If a person “passes” a lie detector test, those results are not admissible in court to show a person is telling the truth.
  • The answers and questions provided during the course of the examination may be admissible in court to impeach credibility under cross-examination.
  • If a jury hears the questions and answers as a statement, they will wonder why they were not given the results.  As a matter of common sense, they will likely assume failure.
  • If a person provides a consistent statement (i.e. polygraph answers) to what their testimony is in court, it is not admissible to show those consistencies.
  • Police may use deception in the course of these examinations by advising a person that they have failed, even if they did not, which may in turn lead to the suspect feeling they must confess.
  • Polygraphs are not as reliable as people and police would like to believe.
  • A polygraph may provide police with “reasonable and probable grounds” to arrest where it was lacking before.

Remember, obtaining legal advice from a lawyer who specializes in the area of criminal law is the essential first step in a proper course of action.  There may be some circumstances where it is beneficial to participate in a polygraph examination, but without speaking to a lawyer, there is no way of knowing the proper approach. 

If you are under investigation and need immediate legal advice as it relates to these, or other matters, please call us directly at (416) 999-8389.

Authors: Sean Robichaud & Chantelle LaFitte