I'm not a lawyer but I believe lie detector tests and their results are not permissible in a court of law. They are not binding and shed no light on whether someone is being truthful or not. Though asking someone who you perceive to be guilty to take a lie detector test is a reliable interrogation technique, the results don't mean anything in a court of law.
Polygraph tests are easily manipulated. It's entirely possible for an innocent person to appear guilty and for a guilty person to appear innocent. All a polygraph test is good for is measuring stress. So when a person who is guilty is lying, their stress level goes up. But the same is true when an innocent person is fearful and answering questions they believe could put them in prison.
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