Using Polygraphs as a Weapon to Extract Confessions

Posted: March 13, 2013 in Failed Forensics
Tags: , , , , , ,

I’ve written frequently about forensic methods that cannot claim to have any scientific validity, yet end up admitted in court and convicting innocent people.  Among these faulty forensics, bite mark analysis probably ranks highest.

But who would have thought that today, we’d have occasion to think about the role played by a forensic method that is almost never been allowed in court as evidence?

It was nearly a century ago that the forerunner of today’s polygraph began to be brought to courts around the U.S. as a fool-proof, scientific method for detecting lies.  Of course, these devices did not do any such thing, and in 1923 the U.S. Court of Appeals for the D.C. Circuit decided the landmark Frye case, keeping the “systolic blood pressure deception test” out of court.

Nevertheless, the polygraph is widely used — by law enforcement investigators at both the state and federal level, and by private parties too.  The fact that criminal courts in the U.S. only rarely accept the results of these tests (New Mexico is the only state that sometimes allows them to be used in criminal cases) seems almost beside the point; the question “if you’re telling the truth, will you take a polygraph?” is frequently relied upon to separate the liars from the truth tellers in the course of investigations.  This seems to be a questionable way of finding the facts, if courts do not accept the result.  But there it is.

But the Chicago Police Department seems to have taken this dubious practice to a new level.  According to an article in the Chicago Tribune, the Chicago P.D.  “used their polygraph unit as a tool to obtain false confessions” by not following national standards and even by lying about the results they obtained.

At least five defendants — four of whom were charged with murder — have been cleared since 2002. In a sixth case, a federal appeals court threw out a murder conviction, leading to the release last month of a Chicago mother prosecuted in the death of her 4-year-old son.  A Tribune investigation found that Chicago police have long ignored voluntary standards for conducting polygraph exams, even as those methods and the examiners themselves have factored into cases costing the city millions of dollars in damages.

Read the article for yourself.  I wouldn’t have thought that in 2013,  polygraphs would feature among the causes of wrongful convictions.  But apparently, at least in Chicago, I was wrong.

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  2. I don’t usually comment a lot on these topics, but the polygraph has always intrigued me. I am not a polygraph examiner (never want to be) but I do train polygraph examiners in interview, interrogation, and statement analysis methods to use in conjunction with the polygraph.
    I will be careful in my response to this topic, but it is my strong belief that the polygraph is best used to screen potential job applicants as some will “come clean” with the truth simply with the belief that the polygraph can actually tell if they are lying (this can be a good thing, especially for security clearance, etc). Whether the examiner or media has convinced them of this, it doesn’t really matter. Numerous people in this country have been convinced that the polygraph is a magic box that can tell if a person is lying. Maybe that’s a good thing for law enforcement, but at the end of the day, it is my educated, experienced, and researched opinion that the courts have made the right decision in not allowing polygraph results as a “fool-proof, scientific method” for detecting lies. I’ll leave it at that….

  3. Peter says:

    Humans can do a lot of things dogs can’t do either, vice versa. This is not a good anology either to compare investigation methods.

  4. Helen Pajama says:

    Shouldn’t those who administer the test be given the polygraph themselves? If a they are crooked,
    all they have to do is say the tests are inconclusive or positive. In death penalty cases it can cost an innocent person to be poisoned to death. And you can’t put Humpty Dumpty back together again.

  5. Tonya says:

    Thank you for writing this! Long have I heard this “if he/she was truly innocent…would have taken a polygraph” as well. I hadn’t realized there were cases of passed tests where the person was actually guilty, but I do know that many times these are quite subjective unless administered by a highly trained professional expert in reading polygraphs, one without an agenda to find either way.

  6. Syed rizvi says:

    What is wrong with using the polygraph as an aid to investigation? After all, we do use sniffer dogs to help investigators, even though they have no testimonial value. I have used the polygraph very effectively to narrow down the search for admissible evidence in major cases. I did not use the results as evidence in any court. When used simply as a guide for investigators the polygraph helps reduce waste of time and money in chasing false trails.

    • The problem with using the polygraph as an “aid to investigation” is that polygraph results are unreliable. Relying on an unreliable technique can lead to serious investigatorial misdirection. Gary Ridgway, the notorious Green River Killer, is a case in point. He was an early suspect in the case, but investigators gave him a pass because he passed a polygraph “test.” Meanwhile, they focused their investigation an an innocent man, Melvin Foster, who had failed the polygraph:

      • Syed Rizvi says:

        Like sniffer dogs, the polygraph is not perfect. Like sniffer dogs, it is not admissible evidence.Like sniffer dogs, it should remain a choice with the investigator.

        • maschke says:

          Sniffer dogs is not a good analogy for the polygraph. Dogs can actually smell odors that humans cannot. But the lie detector cannot detect deception. Using a lie detector is more like slamming a (blank) videotape on the desk and demanding that a suspect explain why, if he was not involved in the crime, a closed-circuit surveillance camera shows him at the scene of the crime. It’s an interrogational prop, and nothing more.

  7. Ron Joy from Ohio says:

    Hello George
    After reading your comment, i had to ask a question.
    There are a lot of companies that when they hire, require a person to take a polygraph test for employment. Suppossedly they want to confirm that you are an honest person and have never lied or stolen from past employers. Although most states differ, isn’t this an illegal practice? Does a person have the right to refuse a polygraph test without having a fear of being denied employment because he/she refused a polygraph?

    • The Employee Polygraph Protection Act of 1988 prohibits most private employers from requiring or even requesting employees or applicants to take polygraph examinations except under very limited circumstances. However, the law has a blanket exemption for federal, state, and local governments. In addition, certain business sectors, such as armored car companies and companies that handle controlled pharmaceuticals may be subjected to polygraph screening. You’ll find the full text of the law here:

  8. With the polygraph, we have the phenomenon of a state-sponsored pseudoscience that has become firmly entrenched in law enforcement and the national security establishment. When decision-makers need advice regarding the polygraph, they turn to those who have the most to hide: their own polygraph operators. So misinformation is built into the system.

    I’m a co-founder of, a non-profit, public interest website dedicated to exposing and ending polygraph-related waste, fraud and abuse. We’ve assembled a great deal of documentation that will be useful to anyone wishing to learn more about polygraphy.

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