It’s a common story for those who are arrested and accused of crimes. They sit in an interrogation or interview with police detectives and hear about lie detector tests. Officers typically use these polygraph tests as a sort of bait to get defendants to confess to crimes. While they make a mighty trick, these tests are almost never admissible in criminal court proceedings. That doesn’t mean that these tests are useless, though. They are often used in various ways during the course of an investigation, and those who face criminal charges should consider calling a lawyer before giving any statement or agreeing to take one of these tests.
Supreme Court jurisprudence on polygraph tests
The Supreme Court of the United States didn’t take up the issue of polygraph tests until 1998. At that point, defense lawyers had been using those tests to put pressure on prosecutors, while police had been using the tests to trick defendants into confessing to crimes. Many wanted to use the tests as evidence in court, and the Supreme Court was asked to weigh in on whether the military’s outright ban on polygraph tests as evidence was a violation of the Sixth Amendment rights of defendants. In United States v. Scheffer, the Supreme Court ruled that the military’s rule on lie detectors did not violate the Sixth Amendment. The Supreme Court noted in its ruling the inconsistency and unreliability of these tests, putting a major dent in their usage in courts around the country.
How polygraph tests are treated in state courts
Very technically, each state gets to make its own determination on whether to allow these tests into evidence. The issue is truly left up to judges. The Supreme Court has held that judges do not have to admit these tests, and in the vast majority of cases today, judges will not allow these tests into evidence. They are never allowed into evidence to prove the guilt or innocence of the accused.
The unreliability of polygraph tests
Lie detectors tests work in a simple way. While they have no ability to detect whether a person is lying or not, they do have the ability to detect changes in the way the body reacts when a question is asked and an answer is given. Research suggests that the body gives off a different, stressful response when a person tells a lie. The problem with this, of course, is that the test is open to error and manipulation. If it is only measuring changes in physiological indicators, then the test can get things wrong. A spike in a person’s blood pressure might mean he or she is lying, but it could mean something else entirely. Judges have found, then, that the polygraph is an ineffective means of proving what it claims to prove.
Beyond that, science has shown recently that the body’s response to telling a lie is not much different from the body’s response when it is highly nervous. This means that when people are nervous as they take the tests, as they often are, the results might be skewed when they tell a lie and when they tell the truth. If the test relies heavily on a person having baseline physiological levels that change with a lie, the test can be wrong when a person behaves in a nervous way as the question is asked. Overall, the unreliability of the tests makes them unfit for admission into evidence in criminal proceedings.
Why are lie detector tests still relevant?
If they aren’t going to be allowed into evidence, why should any criminal defendant be aware of polygraph tests? It’s because they can be used by both sides in ways that can alter the outcome of the proceedings. Police investigators will often threaten defendants, telling them that they will have to take a lie detector test. In some high profile cases, officers have been found manipulating the results of the test to convince the suspect that he or she is going to be found guilty. The goal in these cases is usually to pressure a person into giving a confession.
From the defense perspective, a clean polygraph test can be used as leverage in getting the state to drop criminal charges in some instances. Every case is different, though, so it is critical to have the help of an attorney when the question of a lie detector test comes up. Good lawyers understand how to help their clients when the pressure is on.