The polygraph and false confessions

False confessions are a leading cause of wrongful convictions. According to the Innocence Project, about 25 percent of the documented DNA exoneration cases involved incriminating statements, full confessions or guilty pleas by innocent suspects.

The polygraph is an important tool in the extraction of false confessions. Despite the well-documented inaccuracy of the polygraph, police in North America (less so in Europe and other areas) still rely heavily on the “lie detector” and its even less accurate cousin, the voice stress analyzer, in the investigative process.  If an innocent suspect fails the polygraph exam, police will use the results to persuade him or her that they must be guilty. In some cases, police will tell the suspect that they failed the exam even when they didn’t in an attempt to obtain a confession.

Given the polygraph’s inaccuracy and record of being used to obtain confessions, I am continually amazed to come across cases in which defense attorneys encouraged their clients to submit to a stipulated exam whose results can be used in court, where polygraph results are generally inadmissible.

Polygraph examiners are almost always current or retired law-enforcement officers who are likely to see guilt where a more objective person might not. If the suspect “fails,” the exam, the polygraphist can testify not only that the suspect showed signs of deception but also that he or she supposedly made incriminating statements, exhibited body language suggestive of guilt or used deep-breathing techniques or other measures to outfox the polygraph. As a result, stipulated polygraph exams are usually the kiss of death for an innocent suspect, and many plead guilty rather than face having the polygraph results used against them at trial.

The polygraph industry in the United States, in particular, has done an outstanding job of perpetrating the myth that the polygraph exam is a benign scientific pursuit of the truth. Many people who take a polygraph exam, even if they pass it, conclude otherwise. Karen S. Beers, a respected legal investigator in Colorado, writes about how intimidating a polygraph exam can be and more about the problem of false confessions here. The New York Times has an excellent story about why people confess to crimes they didn’t commit here.

13 responses to “The polygraph and false confessions

  1. You raise a good point, Marty. Three of our clients, including Clarence Elkins and Robert McClendon, were told they failed polygraphs after the crime occurred. DNA testing later proved them innocent. The risks are high, and the ability to manipulate the result is too high as well. When I was a prosecutor, if the suspect took a handwriting test and the “handwriting expert” could not match the sample to the handwriting found in the documentary evidence, the expert could sometimes testify that that the suspect appeared to be manipulating his handwriting, and was writing in an unnatural way, in order to make a match unlikely. There was no science to that, and it was entirely subjective, yet it could have a big impact with the jury. Not on point with polygraphs, but it just goes to demonstrate the lack of science and the ability to manipulate results with some of this stuff.

  2. What if you were denied a polygraph?David Thorne was convicted and sentenced in January, 2000, after being charged with complicity to aggravated murder/murder for hire. There is overwhelming evidence that David was falsely arrested and wrongfully convicted in the death.
    Despite an enormous amount of evidence and numerous statements pointing to David’s actual innocence,
    he remains behind bars. He has proclaimed his innocence from the start. He offered to take a polygraph test,
    but was denied.
    For more information, please visit:

  3. David Thorne’s conviction was based entirely on the false confession of Joseph Wilkes, who was bullied by detectives and threatened with the death penalty. Joe has since recanted.
    Marty Yant did some excellent work on David’s case and has first hand knowledge of what David has gone through. Detectives supplied perjured “witness” testimony and false accusations to back up Joe’s coerced confession. One would expect, if Joe was going to take responsibility for the crime, that he would at least be aware of where and how the crime occured. He was clueless. He got all of the details wrong. Yet no one questioned this.
    David had an iron-clad alibi for the time of the murder, so detectives just filled in the blanks for Joe as they led the 18-year-old through his confession, returning the next day to tweek the details he got wrong the day before.
    David Thorne has been behind bars in the state of Ohio for 13 years this July for a crime he had nothing to do with, based on the confession of a mentally and emotionally challenged kid from the neighborhood, who was “sobbing and shaking in disbelief” during his interrogation.
    Joe replied “I don’t know” or “I don’t recall” 138 times while testifying against David Thorne. He referred to himself as “Joe”. He said he was saying what “they” told him to say.
    Every one of David’s appeals have been denied. Why? Because the system doesn’t believe Joe Wilkes would confess to a crime he didn’t commit. The appellate court said Joe’s recantation couldn’t be believed because he is a liar. Then, in the same document said David was convicted based on the truthful testimony of Joseph Wilkes.

  4. Excellent article. Police always seem to say they use the polygraph as a tool to rule in or out a suspect, but this speculative method has been frequently used in the media – IF the defendant failed, that is. In our case (Jamie Snow), the defendant passed a polygraph in 1994, but was never ruled out. We have been able to obtain the documentation of the tests of two jailhouse informants that took polygraphs well before Snow’s arrest, and the results are blocked out. Obviously they failed them – the state would have been screaming it to everyone if they had passed them. It is frustrating that polygraph results seem to be used only if it is favorable to the state.

  5. One of the major problems with the polygraph is that it is based on a false premise that stress, and consequent activation of the sympathetic nervous system, is evidence of guilt, rather than the stress innocent people feel from being placed as a suspect. In fact one of the major arguments against it is that psychopaths, who present a major problem on both sides of the polizio-judicial system (many criminals and rogue police and prosecutors alike), have a basic defect of part of the brain called the amygdala, which makes them uniquely resistant to anxiety! And of course uniquely convincing liars. So the polygraph is weighted in favour of convicting the innocent and freeing the psychopath. It is small wonder it is so beloved of prosecutors and the systems they control, since they are paid to get convictions, and soft ones of innocent people are the easiest to go for. The polygraph should be banned.

    • Barry Cushman

      Polygraph is not based upon the premise stated. Polygraph simply records physiological activity. Regardless of why polygraph works, we know it does work. (It doesn’t work perfectly, but what test does?) According the the National Academy of Science’s 2003 report on polygraph, they estimated single-issue tests to be about 86% accurate. (That’s well above eyewitness accuracy.) One advocate for the wrongly convicted has researched polygraph exams in exoneration cases, and he found polygraph was accurate – but ignored – in 80%. (That 80% is not statistically different from the NAS estimate.) In regard to psychopaths, the evidence gets in the way here too. There are three studies on psychopaths, and psychopaths were caught at the same rate as non-psychopaths in all of them. (Psychopaths were actually caught at a higher rate than non-psychopaths, but the difference wasn’t statistically significant.)
      You do want to make sure any expert you are using doesn’t have a bias. Your goal is the truth, and we know that means sometimes the state looks at the wrong person. I am an (police) examiner, and I have never done a test for a prosecutor in which the person was prosecuted after a truthful exam. On the flip side, deceptive exams (of which there are fewer) all resulted in some type of plea. Private examiners report many more deceptive subjects, but that’s to be expected. Most lawyers I’ve dealt with won’t subject their clients to a police polygraph unless they are confident of their client’s truthfulness or they know a deceptive test result will help manage the case (in the client’s favor).
      Stipulated tests – the point of this discussion originally – have other factors to consider, of course.

  6. I agree David Anderson. I have a hard time believing in anything more than actual common sense or hard science, if that makes any sense. An ex cop who had watched an interview we did wrote to me and said he was sure Jamie was telling the truth because he was very well versed at reading body language, he also mentioned the voice stress issue as well. And although his support was appreciated, I just don’t find those methods convincing on either side. We get caught up in these things, and they take away from the actual evidence. The facts.

  7. arkansastruthseeker

    Reblogged this on arkansastruthseeker.

  8. In 1996 Jermaine Smothers passed a polygraph. But it wasnt just the lie detector that showed his innocence. When you look at the perjured testimony, the mistaken id, and the lack of any physical evidence linking Jermaine Smothers to the crime. Futhermore, the district attorney would not stipulate to the results so they could be heard by the jury. Even though they asked him to take it in the first place.

  9. Dedicatedprosecutor

    Anyone who thinks that prosecutors get paid for convictions has a distorted sense of the judicial system. I get paid the same whether there are convictions or aquitals.

    I never want to convict an innocent person. However, in many states, including my own, the defense is not required to provide any indication of what the defense is. If a defendant has an alibi- tell me and let me have it investigated. Don’t wait until trial and spring that “surprise” witness on me. If indeed a defendant is innocent, why waste my time, the court’s time, the defendant’s time and the jury’s time by “hiding” that information until trial.

    We do not use polygraphs to determine whether someon is guilty or not. We look at them as a tool which helps us make a decision about CHARGING someone.

    There is a reason they are called polygrpah tests. They are not “lie detectors” , they are instruments which measure specific physiological responses. Those responses may be indicative of deception . . . . But it is an imperfect test. With imperfect examiners.

  10. Pingback: Exoneree Deskovic wins round in suit against polygraphist | Wrongful Convictions Blog

  11. Pingback: Lie Detectors are Voodoo Psychology | CNT News

  12. I have a question for any expert on the matter. As a student in government we recently watched a documentary over 3 – 4 people suspected of rape and murder, 2 of which gave false confessions under pressure of the interrogator. They were sentenced for about 14 years. (I can’t remember the names of the suspects and we didn’t finish the documentary but they possibly could be the people that Mark Godsey mentioned above). During the interrogation, 2 of the suspects were given a polygraph test and a DNA test. One suspect was told they failed their polygraph test when they actually passed while the other suspect was never shown their results of the polygraph test but passed the DNA test.

    As for my question, could either suspect asked for the papers showing their physical results along with the person recording the results to explain the test? I ask this not only because this may have stop the false confessions but also because the interrogator would’ve been charged with forging evidence.
    This research is not for school but more for just common knowledge. So any information would be nice. Thanks.

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