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.
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.
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.
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,  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.