How Lie Detectors Legally Work

It's inventors called it "infallible" -- but they weren't hooked up to the polygraph when they boasted of this controversial device.

Video Transcription

While all the evidence is fresh and the crime is still red on guilty hands, justice gets on the job! Leonardo Killen subjects the suspect to his uncanny invention, the infallible lie detector. The pneumograph with tell tale breathing and blood pressure cuffs to record variations from normal, electrodes to betray the cold sweat of fear. While the polygraph registers the guilty reactions unerringly, the phonograph will make permanent the questions and answers which in court will convict the guilty out of his own mouth! Did you show a knife to the clerk at the ABC liquor store? No! The polygraph is actually measuring an individual’s fear of detection that is what is making the test work because by understanding that there are penalties to being caught in the crime that they committed, self defense mechanisms are activated and this is what we are recording with the exam. In some extreme cases, the chart may put lines off to the edge of the paper and be extremely dramatic, but frankly most exams are very subtle and they require trained eye to even tell the difference between the truthful and the untruthful answers. Although, I realized that it has its limitations in exactly ferreting out whether someone is being truthful, it certainly tells you whether someone is being anxious— And we all carry a lot of baggage up here from a lifetime of experience, and so it may well be that for a bunch of reasons. My results come back inconclusive. Even though it is statistically reliable, it is not statistically infallible. They have been around for what? Fifty odd years, the— The inventor’s pen identifies the verdict. Polygraph evidence is not admissible at a trial. Yes! Unless both sides stipulate or agree that the polygraph will be admitted. You do not see that very often! No! Lies, lies, lies!