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The Polygraph: A criminal defendant’s friend or foe?

The idea of possessing a lie detection machine capable of determining false testimony has fascinated scientists, criminolo - gists and lawyers for centuries. In 1921, the history of deception detection forever changed course when John Larson, a 29-year old Berkeley, California police patrolman, built the first lie detector machine. Larson’s lie detector refined an earlier prototype developed by Harvard lawyer and psychologist, William Marston. Not your typical patrolman, Larson was also a serious scientist with a doctorate in physiology from the University of California. Called a “cardio-pneumo psychogram,” his lie detecting machine measured changes in breathing rate and blood pressure.

It was Larson’s protégé, Leonard Keeler, who dedicated his career to refining the machine into what we now know as the “polygraph.” In 1925, Keeler built the analog polygraph, after years of research and development. In 1936 he added galvanic skin response (skin resistance to electric current), which is still used in modern polygraphs. Since Larson and Keeler, the poly - graph has continually evolved in both complexity and range. But its’ underlying theory has not: when we consciously lie, we undergo measurable physiological changes. And while there’s no such thing as an infallible lie detecting machine, there is such a thing as measuring a physiological reaction that indicates deception.

Most polygraphists use the Comparison Questions Test (CQT) where a suspect is asked so-called “ control” questions with indisputably true or false answers. Is your name Jeff Sessions? Are you Attorney General of the United States? Control question answers establish a physiological baseline against which answers about the alleged crime are compared. The greater the difference, the greater the lie.

As long as there has been a polygraph, there’s been fierce debate about its’ admissibility in the courtroom. Despite the critics and naysayers, there is a sizable and growing body of science that supports the validity and veracity of the polygraph.

This explains the extraordinary status it has recently enjoyed. As depicted in the Edward Snowden whistle-blowing docudrama, the polygraph is ubiquitous; used at every level of government, as well as by private corporations, law enforcement, public and private investigators, and public and private attorneys. And in fact, the federal government, including its’ untold law enforcement and intelligence agencies, is the greatest user of the polygraph in the world, something that is rarely acknowledged.

Despite its’ established use, the judicial system has almost universally judged the polygraph with disfavor, and ruled examination results to be inadmissible at trial. Among the 50 states, there are exceptions. Approximately 15 states admit polygraph results at trial but only if all parties agree to its use prior to the test being taken. Only one state, New Mexico, allows routine admission of polygraph evidence. On the federal level, the polygraph is allowed only at the court’s discretion, with the exception of the 11th Circuit, which prohibits the polygraph without condition.

The two main arguments against the courtroom polygraph orient around reliability and trust.

The polygraph has become a much more sophisticated, complex, and accurate machine since Frye. But the Court’s 1922 decision has stubbornly clung on despite significant polygraph advancements, such as blood pressure, heart rate and voice analysis, and even brain imaging.

Excluding the polygraph on grounds of reliability is an even weaker argument considering the broad spectrum of pattern-matching evidence the court routinely allows from so-called “experts” in such areas as ballistics, fingerprinting, handwriting comparison, bite mark matching, hair examination, blood tests, and carpet fiber analysis.

In modern courtrooms, these types of evidence often turn a case despite unknown error rates and lack of scientific scrutiny. Certainly, polygraph evidence, when viewed in this accepting light, is of no less scientific value.

Trust is the second and stronger argument against allowing polygraph evidence. For no matter how smart, should we trust a machine over human judgment? In State v. Parker, a widely respected Connecticut Supreme Court opinion, eyewitness credibility was found to be uniquely a jury function; allowing polygraph examinations as evidence would “cloud the issue with an aura of scientific conclusiveness...that could foreclose a true consideration of the issue.” The machine engineered to soullessly outpace and outperform humans might be the stuff of thrilling sci-fi, but in the courtroom, treating lie detector results like the infallible ‘Oracle of Delphi’ has met with persistent resistance.

But along this line of reasoning, the routine admission of DNA and fingerprint evidence is just as questionable. In fact, a jury is more likely to be swayed by a dramatic “one in one billion” statistic and “expert” claims about the infallibility of fingerprint evidence, than they are a machine.

The conventional wisdom among defense lawyers is that a guilty client will be found guilty by the machine100% of the time, and an innocent client will be found guilty 50% of the time. Among legal commentators there has been a rising tide of opinion in favor of relaxing the rules of evidence to allow polygraph use in the courtroom whenever the exam is conducted by an experienced, reliable test giver.

The first rule of criminal defense is keep your client from being charged, which is why a favorable polygraph examination can be a defense lawyer’s best friend. Assuming a client has the good sense to hire a defense lawyer before arrest, a confidential polygraph examination provides a singular opportunity to forestall prosecution. The polygraph is given great deference by prosecutors — a fact little known by the public, but widely recognized among defense lawyers. This is particularly true in “he said, she said” situations common in sex cases.

Examiner quality is key. The polygraph, like most pattern matching evidence, is not infallible. In the absence of standardized training and licensure, test quality depends on the skill of the examiner. The structure and content of the questions are the most important parts of the examination. It’s up to the examiner to formulate “control” and “relevant” questions, which can be easily answered with a simple “yes” or “no,” as well as logically distinct enough to elicit a physiological response that indicates deception.

Equally important is examiner confidentiality. As I can attest from experience, many polygraph examiners, if not most, have a background in law enforcement, increasing the likelihood that the results will be leaked to police or prosecutors. To a criminal defense lawyer, a prosecutor’s invitation to use a police examiner is a red flag, as they are skilled interrogators trained to manipulate questions to show guilt.

A polygraph examination need not go in front of a jury to carry enormous weight in a case’s official assessment. Trial judges have wide discretion at the time of sentencing to consider polygraphs along with virtually any other information they choose. The same applies in criminal forfeiture proceedings. Moreover, a good defense lawyer knows that when a favorable polygraph fails to persuade a prosecutor to dismiss a case, then taking it public by way of courtroom motion or media disclosure can dramatically change a case outcome.

Lie detector technology continues to develop in sophistication and accuracy. With the institution of national examiner standards and new state procedural rules designed to ensure reliability, supported by rapidly evolving brain-based technologies like electro encephalography (EEG) and functional magnetic resonance imaging (FMRI), it is becoming more and more difficult to ignore or discount the validity and veracity of the polygraph.

Given our government’s institutionalized use of polygraphs, and judicial acceptance of other evidence that is less reliable than the polygraph, the best approach might be to allow this machine into the courtroom on a case-by-case basis, subject to vigorous cross-examination and other tests of reliability. In cases where there are no exculpatory eyewitnesses or alibi evidence, and a polygraph is the only effective means to prove innocence, it should be allowed. Indeed, no one should be denied the constitutional right to present a defense.

A lawyer worth his salt will not turn his back on the polygraph. An intelligently handled polygraph can be the criminal defendant’s best friend.