In Hilaire Belloc's poem 'Matilda', we read: 'Matilda told such Dreadful Lies, It made one Gasp and Stretch one's Eyes.' Unfortunately for law enforcement agencies and other investigators, most lies are not quite as obvious as Matilda's unless a polygraph examination is conducted. Polygraphy is just as important in determining innocence as it is in proving guilt. The polygraph instrument, or 'lie detector', as it is more commonly known, is a scientific instrument used to establish whether or not an individual or suspect is being truthful with regards to a specific issue or crime. It records physiological responses as a result of a stimulus, in the form of specially designed and structured questions, which are put to the subject or examinee whilst attached to the instrument. The polygraph is used by law enforcement and intelligence agencies world wide, and forms an integral part of many investigations.
The polygraph examination - a three phase procedure

Polygraphy involves three distinct phases - the pre-test interview, the instrumentation phase and the post-test interview.

1. Pre-test interview

During the pre-test interview, the polygraphist reviews the questions that will be put to the examinee during the instrumentation phase, as well as asking background and medical history questions. This is done to ensure that the examiner is aware of all factors contributing to the examination as a whole.

2. Instrumentation phase

During the instrumentation phase, the examinee is attached to the instrument and the questions reviewed in the first phase are posed while a permanent recording is made of the examinee's psycho-physiological responses to each question.

3. Post-test interview

In the third phase the examinee's results are discussed with them and all efforts are made to obtain a confession from the deceptive or "guilty" party. A good polygraphist is thoroughly trained in techniques of interviewing and often elicits information withheld by examinees in previous interrogations.

Admissibility as evidence

There has been no South African ruling on the admissibility of polygraph results per se, though there have been several cases in which evidence has been presented concerning confessions obtained as a result of a polygraph examination. In all cases, the court held that the confessions were valid. In a recent case in the USA, a United States District Court Judge, FA Little Jr, ruled the results of polygraph tests as admissible. The ruling was in keeping with a recent decision of the Fifth Circuit Court of Appeals (US v Posado, 57 F.3d 428 (5th Cir. 1995), which in turn depended on the decision of the US Supreme Court in Daubert v Merrell Dow Pharmaceuticals (113 S.Ct. 2780, 1993). In his decision, Judge Little said that lie detector tests, while not infallible, have a good record of accuracy when admitted by licensed testers and are now widely used in Industry and Government.

History of Polygraphs

The first modern polygraph was constructed in 1921 by John Larson, a medical student at the University of California. Larson developed the instrument in collaboration with a member of the local police department. It was capable of continuously recording blood pressure, pulse and respiration. Certain alterations from the examination norm in these measures have been proved to be linked with deception or guilt. Because it recorded the three variables as graphs, the name polygraph was coined.

A later development enabled the device to record the psychogalvanic skin reflex, which is the flow of electrical current between different parts of the body - another gauge against which "unusual" changes can be measured.

Today, the polygraph is acknowledged as having provided the most dramatic advances in interrogation technology, and correctly applied it is at least 98% accurate. Polygraphy is used extensively by private and public law enforcement bodies in the USA, United Kingdom, China, Japan, Germany, South Africa, and many other countries.

Case Study I

In one case, a driver collected R4 500 cash from a furniture retailer's branches and delivered the money to the main branch. There, two female employees counted the money and placed it with other cash collections in two bags for banking the next day. The same driver took the money to the bank, where it was found to be R4 500 short.

The three employees were examined by O F & A's polygraphists, and it seemed likely the driver would fail the test. However, it was one of the women who appeared evasive in the pre-test interview, and she was the first to be tested. She failed the examination and confessed to having stolen the money, which the other woman had inadvertently failed to place in the banking bags before they were put into the safe.

This is a good example of the value of polygraphy. Without it, the driver would almost certainly have been the subject of everyone's suspicion.

Case Study II

In another case, a company safe containing R8 000 was locked, as usual, one Friday night. On Monday morning it was discovered that the cash was missing. A window had been broken and it appeared as if the safe lock had been picked.

It struck O F & A's investigators as strange that nothing else had been stolen, and suggested that the two managers, the only key-holders to the safe, should undergo polygraph tests. One passed conclusively, while the other failed. The investigators then questioned the deceptive manager and he confessed to having staged the apparent burglary over the weekend.

This case is a typical example of the value of polygraphy in the absence of witnesses or physical evidence.

Case Study III

In this case, the company employed O F & A following a theft of a large number of engine components of high values. At the outset it was apparent that the security guards at the premises were involved as the components were too heavy to be thrown over the well-secured and electrified perimeter. In addition, there was only one exit, which was guarded on a 24-hour basis.

Over the weekend in question, there were seven shift changes, creating a fairly wide group of possible suspects. O F & A decided to randomly subject the security guards to a polygraph examination. Simultaneously, several employees were given polygraph examinations as it was suspected that one of the perpetrators of the theft had a key to the warehouse containing the engine components.

One of the security guards failed the polygraph examination, and admitted to his involvement - letting an employee onto the premises to perpetrate the crime - only a few days later. Further questioning revealed that the employee, who the guard had let into the premises, was the same employee who had failed his polygraph examination. When the employee was confronted with the guard's confession, he too confessed to having perpetrated the theft.

The above illustrates the effectiveness of the polygraph to isolate suspects in a large group of people, thus speeding up the investigation and producing results in as short a time as possible.

O F & A's Expertise

O F & A's two polygraphists are Members of the American Polygraph Association, which is the most respected and recognised international governing body for the profession. They are also members of the Polygraph Association of South Africa. Both are studying towards law degrees, which provides them with insight into the legal technicalities that surround interrogation, confessions, and criminal procedure in general.