Polygraph Test Result in Zimmerman Case is Unreliable and Useless

The Sanford Police Department concluded that George Zimmerman passed a voice stress analysis test, which is a type of polygraph test.

How much credence should we place on the result and will it be admissible in court?

Although police routinely use polygraph tests when questioning a suspect in order to confront the suspect, if the test indicates he is attempting deception while responding to a question, the United States Supreme Court and many other state supreme courts have held that polygraph test results are not admissible in court because they are not sufficiently accurate and reliable.

For background information on polygraph testing, go here.

Florida excludes polygraph test results. Therefore, the results of Zimmerman’s test will not be admissible at Zimmerman’s trial.

Nevertheless, many members of the public now know that he passed a polygraph test, so let us take a look at his test and see what conclusions we can draw about it.

Yamiche Alcindor and Marisol Bello reporting for USA Today said:

Zimmerman was asked nine questions, including two related directly to the shooting: “Did you confront the guy you shot?” the tester asked. “No,” Zimmerman responded. “Were you in fear for your life, when you shot the guy?” the tester asked. “Yes,” Zimmerman said. The examiner concluded that Zimmerman “told substantially the complete truth.”

Ron Grenier, a former FBI agent and lie detector expert, said the voice stress analysis test is not as reliable as a polygraph test. Also, he said, it’s unclear what the examiner meant by “confront.” Further, such tests don’t measure a person’s state of mind or fear at some other time, he added.

“He may have convinced himself that he was in fear of his life, but whether or not he was is not definitive,” Grenier said.

Zimmerman’s responses would be more meaningful, he said, if he had been asked, ” ‘Did Trayvon Martin attack you and knock you to the ground?’ Or ‘Was Trayvon Martin on top of you hitting you before you shot him?’ ”

Joe Navarro, a former FBI agent who teaches interviewing techniques at Saint Leo University, agreed. “You have to ask precise questions,” he said. “You want to know at what point you feared for your life.”

I agree with Ron Grenier’s criticism that the question, “Did you confront the guy you shot?” is an improper question.

The question is vague because it is too subjective to be of any use in determining whether GZ followed TM and was the aggressor. Note that the legal test for self-defense depends on the objective circumstances of the encounter between GZ and TM and whether a reasonable person in that situation would have concluded that it was necessary to use deadly force to prevent imminent death or grievous bodily harm.

A confrontation can be verbal or physical and GZ may have believed or convinced himself, without any rational basis for doing so, that TM’s presence in the neighborhood and his attempt to elude GZ justified GZ in attempting to prevent him from getting away. Therefore, GZ might have perceived any resistance by TM as a confrontation, even if TM were merely standing his ground and using force to defend himself.

Similarly, the test result does not help us determine if GZ was the aggressor.

I also agree that the question, “Were you in fear for your life, when you shot the guy?” is improper because whether he was in fear of losing his life when he shot and killed TM does not help us determine if a reasonable person in his situation would have been in fear of losing his life.

The test result is basically useless because to decide this case the ultimate finder of fact will have to decide what each person did and whether a reasonable person in GZ’s situation would have done what he did.

Finally, even if proper questions had been asked, there are any number of examples of guilty people who passed polygraph tests. One person with whom I am familiar is my former client Gary Ridgway, the Green River Killer, who passed a polygraph in 1987 when he denied being the Green River Killer. He was released and continued killing until he was arrested in the fall of 2000, after DNA test results implicated him in several homicides.

Due to their proven inaccuracy and lack of reliability, I do not support using polygraph tests for any purpose and I think police departments and all employers should be prohibited from using them.

20 Responses to Polygraph Test Result in Zimmerman Case is Unreliable and Useless

  1. ed nelson says:

    Fred, thanks for another insightful post, please feel free to delete my above rangey comments, which I neglected to tie to the subject of “Lie dectors”, which should have been that:, in the above minor incident… I was implored as to whether I would be willing to take a polygraph, when Police questioned me on my wherabouts on that evening, and didn’t seem to take my word for the fact I had been in bed asleep. I said: “sure I’ll take the test”, even though not in very good shape, physically sick and shaking like a leaf from being rousted from the first sleep in a couple of days.

    Yeah please delete that it doesn’t help much, I had my car vandalised over night just hours after posting the comment ( fouth time in 5 years, same hybrid car, same MO, big rocks on car and drive off in the we hours, ). And I reported to a nice police officer this morning, So, uh I am on the side of law and order, just to clarify that.

    The incident that I referred to was upsetting to me, for a number of reasons. This kind of whole cloth frivolous accusation by a person I never even met or talked to, who was in military surveilance school near here. this 20 something guy living in a “inlaw apt with his girl friend (who wore a Dixie flag sweater), barked at the city police about… “he means business!… ” and so on, he was feeling his oats about the power of being a fed, it seemed like. Well they need to be tough they have to go on ships and deal with the crews and officers of all mannor of situations on the high seas, but hey leave the neighors out of it… if you please Bubba.


  2. ed nelson says:

    We in my neighborhood school back in the 1950’s were told… the fact that that the so called “lie detector” was a scam. We were told by our teachers that “Lie Detectors” were a ruse… a false thing… and a fraud!!

    So sorry to you dweebs of the large continent… so sorry you are so stupid!!!

    • Ed, I don’t think anyone here believes polygraph tests produce accurate and reliable results.

      • ed nelson says:

        Sorry Proff Freddie… I am still pissed off from a little deal that occured here on july 18, 2003. at about 2 AM. I was sound asleep, didn’t have a drop to drink… that night!! No, because, I was under a great sikness of Hey fiever, I got really sick from chopping down the dry weeds in the little back yard that I got.

        This coast guardsman next door accused me of sneaking around their place, and there were about 6 police cars and a whole bunch of cops here, [petaluma, Ca. July 18, 2003. ]

        I let the cops in and let them go look around to their heart’s content, and all she came back with was… “Oh so you have a weapon… ?

        So I says… yah I guess i do… table leg fish getter, hell that ain’t the weapon. ( I thought she found my piece… I got a couple of em, and gettin’ some more too…

  3. CommonSenseForChange says:

    Those were “placebo” type questions used to measure voice stress when lying.

  4. Patricia Fritz says:

    Isn’t question #8 on the “polygraph” a TRICK question?

    I.E., if a subject would lie on #8, the subject would lie on anything. It’s not that it’s an insignificant question, because if your veracity is in question in connection to a homicide, EVERY question has significance and you would want to be VERY careful to tell the truth.

    Question #8 asked Zimmernan if he had ever exceeded the allowable speed limit. Zimmerman;s answer: No.

    Zimmerman, at 28 had likely been driving a vehicle for 12 years. In TWELVE years he had NEVER edged over the posted speed limit … not even once? ARE YOU KIDDING ME?

    Isn’t that question there as a check to the subject’s truthfulness? Answer for 100% of the driving population would be “yes.”

    But Zimmerman answers “No.”

    This would tip ANY law enforcement agency that Zimmerman can’t be believed. I’m just wondering how many subjects answered that question the way Zimmerman did. Any stats on that?

    (Incidentally, why the question about the “green wall?” Strange question for a police test that wuld be administered to males, with a significant number, statistically, having red/green color blindness.)

    While there may be readers who see my post as judgmental against Zimmerman (supposedly, that I’m a poster who is either liberal or Black), FYI I’m a white, 78-year old, long-time registered Republican, who has owned handguns/shotguns for decades. Briefly, with police permission, had an AK-47 in the 70’s.

    Just looking for the truth, thanks …

  5. crazy1946 says:

    Professor Leatherman, Would the perscription drugs that Zimmerman affect the results of the tests given to him? Any guess to the affects they might have to his sworn statements? Could they possibley affect him in such a way he actually believes his own story even after parts have been proven to be not true? If the medical report from his doctor is entered into evidence (and I am sure it will be by the defense) does that open the door to enter into the record his one arrest, the one where he allegedly was ordered to under go anger managment treatment? Thanks for taking the time to keep us all alerted to the in’s and out’s of this case!

    • In reverse order the medical report probably will not be entered into evidence, but the doctor will be permitted to testify and, of course, can be cross examined regarding the material in the report. Inadmissible evidence such as GZ’s description of who did what to whom and in what order will not be admissible because it is hearsay. The reference to an arrest and a referral for anger management probably will not be admissible because it is prohibited as propensity evidence by evidence rule 404(b).

      The drugs he was taking do not cause psychosis. Adderall is a mild amphetamine prescribed for ADHD. Tomazepam is a benzodiazepine prescribed for insomnia (to sleep) and to prevent seizures. The combination he was taking is prescribed to help people function at a higher and more efficient level, not to debilitate. Therefore, I do not believe the meds he was taking would have affected his behavior at the time of the shooting or while he was taking the voice stress analysis test or giving statements to the police.

      • jduu says:

        Sociopaths are known to be able to pass lie detector test with verifiable lies. From what is being revealed about GZ, he seems to fit the description.

        Take a look at: http://www.vodahost.com/web-hosting-sociopath-test-sociopath-definition.html/

      • ed nelson says:

        that is right, I read a coulple a books on that… One that I liked was: “the sociopath next door” and that was something that all thinking folks should read… because the bottom line there, is, to me, anyways: that, sociopathy isn’t unususual. On the contrary, it is not unusual, but is maybe something quite usual, to the extent that even…. that there may be some amount of sociopaths, something like maybe… : 6% of any human population!

        Think of it as 6 sociopaths in every 100 people, sounds about right to me, The book, tells of how most of these “sociopaths” are quite well adjusted to their surroundings, and are the last to be put under a scope/ or to be interigated….

        Because they are the perps buddy.

        There is a contingent of bad…. Bad ass to the bone… Bad seed is one way it was said, but bad ass… mainly is my point!!

      • renosweeney says:

        I’m sorry, but Adderal takes a while to adjust to and constantly has to be managed. Just missing one dose can cause anger and agitation issues. Being on Temazepam makes it that much harder to manage

  6. Marilyn says:

    Mr; Leatherman, thank you so much for explaining the difference between polygraph and what the SPD did. I know this is off your topic but I have another major matter that also doesn’t seem to be being addressed:

    I’ve run into a puzzler. Witness #6’s credibility needs to be examined a little more carefully. On his 911 call he starts by saying, “I just heard a shot right behind my house.”
    The shot was fired at 7:16:56 pm and he connected with 911 at 7:18 pm so this is an accurate statement. Exactly 1 min. & 4 sec. earlier, he had heard the shot. Part of this one minute delay could have been because his fiancé (or someone) was already on the phone. It is a significant interval however, as he had just warned the combatants that he was going to call 911.

    But here’s the mystery. On Witness #6’s sworn police statement dated March 20, he says that after he went back inside he first told someone to get off the phone. He then locked the door and dialed 911. The statement he signed explicitly says “while on the phone with 911 he heard a gunshot or what sounded like a rock hitting the window,” This, according to the statement, was as he started to run upstairs while on the phone with 911.
    The oral statement he gave the same day is in concordance with the written statement released by the police. Orally he says that as soon as he picked up on 911, a couple of seconds later, is when he heard the shot. There is no doubt in either statement that he says he had already connected to 911 when he heard the shot.

    Witness #6 made his 911 call starting at 7:18 pm. This was 1 minute and 4 seconds after Treyvon Martin was shot. So he’s sworn the shot was fired at 7:18+ pm, both orally for the police tape, and in his signed evidence statement. He’s stated this almost a month after the shooting, so he had ample time to get his facts straight. How can we believe anything else he says?
    What was Witness #6 doing at 7:16:56 pm when the shot was actually fired? It’s easy to prove that he was not calling 911. Witness #6 has already recanted and changed other testimony. How credible is he when he wrongly continues to swear to something as important as the time of the gun shot?

    This witness is all George has. Those defending George continuously cite the MMA style fighting quote as proof that Treyvon had George subdued. But how can we believe Witness #6? We don’t know what happened from anybody else’s testimony at the time of the actual gun shot, and now we can’t trust Witness #6 either.

    • Of course, a jury eventually will decide whether the witness is credible, but I don’t believe he is credible because he has recanted his testimony.

      Basically, I wouldn’t believe anything he says because he obviously made up some of the stuff he told the police. Like the MMA stuff.

      Why pick and choose stuff to believe or not believe when he has admitted making important stuff up?

      He has his own agenda and has proven that he is not reliable.

      Yes, that leaves GZ without a credible eyewitness to support his story.

  7. jd says:

    Clearly the voice stress test was a ruse by investigators to get GZ on the record one more time telling his narrative to a different investigator. The “results” are evident – GZ continues to produce contradictions and inconsistencies in his statements to investigators that fly in the face of the logic suggested by his recorded call to non-emergency.

    That’s the whole purpose of a “voice stress test:” to get the suspect to keep talking. Nothing more and nothing less. Any fool knows they are useless in a court of law.

    Here are the “results” of the voice stress test:

    GZ: “and i went to go for my phone instinctively and call 911
    …jacket pocket.. etc…and i reached and i was looking for my phone.. and he just punched me in the nose, and i fell backwards and to my side, and he ended up on top of me” etc (sorry I haven’t fully transcribed the dialog.)

    This statement is of course in complete opposition to how he characterizes the start of the fight during his walk thru, where he does NOT fall backwards, but instead stumbles forward for thirty feet or so (actual distance is more like 50).

    Once again here is the result: he’s contradicted himself and one or the other statements, or both, are lies he told to investigators.

    • Your comment reminds me of a story I heard about a small town police department in eastern Washington State that could not afford a polygraph, so they used colander connected to several wires by alligator clips.

      The wires weren’t connected to a machine. The ends just dangled loosely inside a shut drawer in a detective’s desk.

      He fit the colander on a suspect’s head and every time he got an answer he didn’t believe, he told the suspect the machine said he was lying.

      Got a lot of confessions that way for a whole lot less money.

  8. CommonSenseForChange says:

    Love your blog Professor Leatherman!

    One thing I had noticed early on once the evidence was released is that Zimmerman was only asked if he saw Trayvon Martin looking AT houses in the useless poly. In other interviews, he says Trayvon Martin was looking INTO houses and I think he even says this INTO houses crap in his written statement.

    The poly won’t be admitted anyway, but I found it odd that Zimmerman alternated from AT to INTO depending on his need during different police interviews to make Trayvon Martin more evil when it suited Zimmerman to tell his story that way.

    • That’s one way to tell whether a person is lying.

      Not every inconsistency indicates lying, but when all or most of them create a recognizable pattern that exclusively benefits the story teller, at the very least you’ve got some exaggeration going on and at worst intentional deception.

      Intentional deception regarding materially important matters, such as the one you spotted, indicate lying to me.

      Nice grab.

      • CommonSenseForChange says:

        I’m with you on that. It also shows that the tests and test-takers aren’t necessarily detail-oriented or up to snuff. I think that’s part of the reason the test results aren’t permissible in court. The test, the questions and the answers aren’t valid.

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