Inconclusive: The truth about lie detector tests
Investigators in Jacob Wetterling's disappearance used lie detectors "a lot," one of them says. But some research suggests they're not much more reliable than flipping a coin.
The police subjected Jacob Wetterling's parents, Jerry and Patty, to polygraph testing after their son was abducted in 1989. "It's horrible," recalled Patty, who was tested by the Minnesota Bureau of Criminal Apprehension. "They wire you up. They ask you a bunch of questions to get a base line. 'State your name. State your age.' And then they will ask you a question like, some ridiculous thing, 'Have you ever lied?' Which is, you know, everybody has."
Jerry took the test twice. And he knows he failed on at least one question when asked whether he was "withholding any information in regard to Jacob's case." He said no.
"The minute I said it, I was thinking about, 'Oh yeah, there is the psychic.'" Frustrated with a stalled police investigation, Jerry Wetterling had consulted psychics about the case. He didn't tell investigators, figuring they had enough leads and wouldn't have considered psychic insights serious evidence. The polygraph examiner rephrased the question at Jerry's urging, asking, "Aside from psychic information ...." When he answered that time, he said, he passed. Polygraphs — which measure changes in heart rate and blood pressure, breathing patterns, and skin conductivity via sweat in an effort to determine whether someone is lying — were used extensively in the Wetterling investigation, on suspects and potential witnesses. The test subjects included Dan Rassier, who lives on a farm near the abduction site. Rassier recalled the experience as "pretty flimsy stuff" compared with what he'd seen on television.
Despite the continued employment of polygraph testing by law enforcement, the tests don't reliably or consistently work. They are considered by many in the scientific and legal communities as only marginally more accurate than coin flips. Consequently, most courts do not admit polygraph evidence.
"The statistics on it aren't very good across the board, historically or now," said Melissa Littlefield, a researcher and associate professor in the departments of kinesiology and community health, along with English, at the University of Illinois. Littlefield wrote a book on the topic in 2011 titled, "The Lying Brain: Lie Detection in Science and Science Fiction."
The American Polygraph Association, which sets standards for testing, says that polygraphs are "highly accurate," citing an accuracy rate above 90 percent when done properly. Critics, however, say the tests are correct only 70 percent of the time.
It's difficult to definitively assess how well lie detectors work because there are many definitions of deception and many ways of measuring the results, including those deemed "inconclusive." But a skeptical 2003 report from the National Academy of Sciences found that polygraphs work at rates well above chance, though far below perfection. "Almost a century of research in scientific psychology and physiology provides little basis for the expectation that a polygraph test could have extremely high accuracy," the report said. Nonetheless, the tests are currently used by law enforcement in criminal investigations; by federal agencies to screen potential employees and by probation officers to supervise sex offenders.
Guilty people in notorious cases have passed the test. They include Gary Ridgway, known as the Green River Killer and the Russian mole Aldrich Ames, who used so-called "countermeasures" to beat polygraphs twice in the 1980s and early 1990s. Ames' recipe for success? Get a good night's sleep and be nice to the polygraph examiner. Conversely, innocent people have failed the polygraph, like Bill Wegerle, who was suspected of killing his wife in 1986 until DNA evidence traced the murder to BTK killer Dennis Rader.
Polygraph tests are "really valuable for lead information, or for further investigation," said Al Garber, a former FBI agent and U.S. Marshal for the District of Minnesota, who led the early phase of the Wetterling investigation. "They're not admissible in court as we speak today, and the reason is that it's not an exact science. But they are very valuable for an investigator. They can tell you which way to go in a lot of cases."
A precursor to the polygraph was first used in 1921 by psychologist, lawyer and inventor William Marston, who later created the comic superhero Wonder Woman. A man named James Frye had been accused of murdering a prominent physician in Washington, D.C. He had confessed to the crime and then recanted his confession. Marston used a blood pressure cuff on Frye while asking him questions and measuring his physiological reactions. He claimed his test showed Frye to be innocent, but a judge in the case refused to admit the results as evidence, citing a lack of general acceptance by the scientific community. The ruling established what came to be known as the Frye standard, which governs expert witness testimony in many states, including Minnesota, to this day.
Garber acknowledged that sometimes he's not after polygraph results as much as a person's reaction to the idea of taking the test. "You can tell a lot by when you talk to someone and tell them, 'We'd like you to take a polygraph,'" he said. "Or, 'Here's a way to make us believe that you're telling us the truth — take a polygraph.' You can tell a lot from a person's reaction."
The crystal ball, sodium pentothal, mental telepathy, Wonder Woman's lasso of truth: American culture is fascinated with the ability to look into a person's mind to see what's really there. "I am always tempted to say, it's not bad or good science," said Littlefield, the Illinois professor. "It's not a question of whether it works. It's a question of why we want it to work. Why are we so excited about the idea of hooking people up to a machine and seeing if they are telling the truth?"
A belief persists, she said, with roots in mind-reading experiments conducted in the mid-20th century, "that thoughts could somehow be made manifest outside the body. If we could capture it, then we would know something more than we know. It's the idea of a sixth sense. There is information that we can't access with our senses and we have to find another way to access it."
The lie detector test hasn't changed much since it was invented in the early 1920s by John Larson, a medical student at the University of California and a police officer, who eventually withdrew support for his own invention. A person is placed in a chair with galvanometers hooked to their fingers to measure sweat, a cuff around their arm to measure blood pressure, and pneumographs strapped across their chest and abdomen to measure breathing. One major innovation is that, today, readings based on question responses are fed into a computer rather than scratched out on paper. The examiner looks for spikes or changes in readings during moments when the subject is struggling to make up a lie to cover the truth. (There have been recent efforts at measuring brain activity to ferret out lying — going directly to the "organ of deceit" — through functional magnetic resonance imaging, or MRI, but the method hasn't caught on.)
The premise is that people behave differently, and predictably, when they lie. But that's not necessarily the case. The polygraph measures autonomic responses, "and that is all it is measuring," Littlefield said. "Everything else is interpretation. If you want to look at a record and say, the blood pressure increases when asked this question, that could be for multiple reasons. There are a lot of reasons why your levels and physiology go up and down." Those include hypoglycemia, fear, confusion, PTSD, nervousness, alcohol withdrawal, psychosis and general anxiety. Tellingly, in her own experiment, Littlefield found that a person's body can trigger similar test results when undergoing "stressful truth telling" as when lying.
In some contexts, whether the tests work is beside the point, as they are often used simply to scare suspects into confessing to crimes or to drive away job applicants with secrets. Littlefield cited examples of people duped into coming clean while hooked to a box with green and red lights on it and even to a copy machine. "It's the idea of the machine," she said. "Whether or not it works, it gets people to cooperate."
Garber, who said the polygraph was used "a lot" during the Wetterling investigation, remains convinced of its value in exposing deception. "It has to be voluntary, first of all," he said. "There has to be a reason to polygraph them. I mean, someone gives you an account of what they saw and it seems reasonable and they seem reasonable, you don't polygraph them. Someone gives you conflicting information, they tell you something and you know it to be false or at least inaccurate, that's a reason."
Certain people, he said, fear the test because they "don't believe in the polygraph and they're afraid that the polygraph will show something that's really not true." Usually, though, when a suspect or witness declines testing, it's for darker reasons. "If they say, 'I'm not taking any polygraph,' naturally it makes you believe they must have something to hide."