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Three Former Crown Prosecutors

Are Lie Detector Tests Admissible In Court For Canadian Criminal Law?

A common question that clients asks me is whether a lie detector is admissible or whether that will help under the Canadian criminal law.

The short answer to that is that a lie detector is not admissible in court. It cannot be used either for you or against you. So for example, if you agreed with the police to take a lie detector and you pass, a judge is never going to hear about that. If you fail, a judge is never going to hear about that.  The lie detector is often used by the police as a tool to get you talking.  You should not take a lie detector, if the police ask you to do that. What’s going to happen is that they could a) lie to you and say you failed and try to get you talking get you nervous, even if you pass, it doesn’t help. There may be very narrow circumstances where you might consider a lie detector and I will give you one example that I have used for clients in the past. 

The crown is thinking about withdrawing the charges, they think it’s a very weak case, and they’ve had discussions but they are saying, “you know, we are going probably go ahead with it”, the victim wants to ahead, I recognize it’s a weak case, maybe there’s some slim prospect of a conviction, maybe there’s not, but politically the crown wants to go forward. In that situation, I might, and I have done this a couple of times, in the past, with clients in that situation, hire our own lie detector expert. So then we do that in our office with the expert or the expert’s office, if the person passes, I may be able to then, you know, use those results to the crown, “look you got a weak case, you know it, you’ve already told me you don’t want to run this case, he’s passed the lie detector, he’s innocent.” That situation rarely happens but that’s the only time, it’s our own lie detector and if you fail it, and there are false fails on the lie detector, even if you are telling the truth, it’s not infallible, we don’t share it with anyone.  So other than that very narrow situation which rarely happens, do not ever agree to take a lie detector, especially from the crown or the police. That is not a situation to get into, you have the right to remain silent and that’s only going to probably hurt you by taking that lie detector test.

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