Criminal polygraph examinations

The polygraph, or as it is still informally called, the lie detector, appeared in its original forms in 1875 when Italian physiologist Moso studied the fear and his influence on the work of the heart and breathing. By investigating fear, he found the so-called. An ergograph, which recorded muscle tension, is similar to a pletismograph that records the change in pulse and blood volume. After his invention, and many other scientists from different areas have dealt with this issue and the advancement of “detectors of lies”. The polygraph we know today is the work of the American scientist Larson, which does not differ much from today’s polygraph, other than some technical improvements. (Bulka, 2012)

How to use it?
Poligraf is an apparatus that in the conditions of a special psychological situation, which is caused by the questions of the examiner, simultaneously registers several autonomic physiological reactions of the organism of the respondents. (Milan Žarković, Božidar Banović, Ljubinka Stupar, 2005).

The physiological reactions measured by the polygraph include: heart rate (pulse), blood pressure, depth and breathing rate, skin moisture (galvanic reaction), circulation and peripheral blood vessel oxidation. Registered changes can be monitored either on the screen (in modern polygraphs) or in polygraphs (moving paper where reactions are recorded with the printer). “In order to record a change in blood pressure and pulse, rubber pads are used (similar to that of the pressure measuring device). In order to register breathing changes, a rubberized, ribbed and easily extensible hose is filled with air. To register changes in the galvanic reaction (moisture of the skin), a tile with two electrodes is placed on the palm of the hand, which releases very low intensity. To record the oxidation of blood vessels and their volume, photosensor is placed on the finger of the hand. “(Milan Žarković, Božidar Banović, Ljubinka Stupar, 2005).
Poligraphic examination can be conducted for all criminal offenses and against persons of both sexes. There are also persons who are unsuitable for polygraphic testing. These are persons with very low or high blood pressure, heart patients, persons with hearing impairment or vision, with various diseases of the respiratory organs, mentally ill persons, in the postoperative state, under the influence of alcohol, narcotics or certain drugs, hungry, unexplained and exhausted persons . Polygraphic testing is based on a voluntary basis, ie, Voluntary consent of the person to be examined is required. This consent is in the form of a written statement that a person agrees to polygraphic testing.
Before testing, the examiner tries to obtain as many of the relevant facts and figures as possible about the criminal offense, as well as the personality of the respondents, in order to adequately test the questions that will be posed to the respondent. An introductory conversation with the respondent aims to calm the innocent person, and to arouse and reinforce the reactions to the culprit, so it is often not uncommon for the perpetrators to admit the work before questioning. The very beginning of the examination starts with the explanation of the polygraph respondent, its attachment to the apparatus, instructions to not make sudden movements, looks right in front of him, corresponds briefly with “yes” or “no”. After that, it starts with asking questions which should not be more than 10, and which are set by the same voice intensity and at the same time interval of 20-25 seconds.

Questions and reactions
There are two models of polygraphic testing: direct and indirect. In the case of a direct, suspect, all relevant facts of the offense are known, while in the indirect, the respondent states that these facts are unknown to him. We can share the test questions ourselves with: critical questions, control issues, complexity issues and irrelevant questions.
Critical issues are those related to a criminal offense, or some detail of a crime that is known only to the perpetrator. The person who is the perpetrator of the act will have a reaction to this question. The control question is directed at something the respondent actually did but refuses to recognize. This question is chosen so that it is known that the interviewed person will give a false answer, and then he will get excited. The question of the complex of guilt is constructed so that the examined face is brought into conjunction with the fictitious part of a certain type and weight in order to produce the reaction of that person that something that has not been done is charged him (Milan Žarković, Božidar Banović, Ljubinka Stupar, 2005).
1. If the reaction to control issues strengthens the response to critical issues then the polygraph indicates innocence;
2. If, in turn, the situation is reversed that the reaction to the control issues is lower, and the critical stronger, then one can be guilty of guilt;
3. If the reactions are alike, then it is a borderline case that indicates that the test needs to be changed;
4. If the reaction to the control issue is weak, and when asked about the complex of guilt, this reaction is far more pronounced, then it is an innocent person.
The responses of innocent people will be greatest on control issues because they only agree on these issues, while the response to complexity issues and critical issues will be less. Very low reactions will show these irrelevant (unimportant) questions.
Of course, such definitions can always be objected that such an interpretation is not always correct because it raises the question of whether more responsive to controlling or critical issues, or who will be more frightened by the respondent. There is also an objection that in psychologically ill people the reaction to the questions is sometimes the same as in the case of guilty (Bulka, 2012).

Polygraph does not disclose a lie as such, but registers appropriate physiological reactions which are considered to be typical of a man’s manifestation of excitement and stress, which arises when the truth is not told in relation to a particular question (Pravni portal, 2014). In our criminal law, the polygraph is not an evidence and can not be used in court as such, but serves as an indication that will reduce the circle of suspects, direct the investigation in a certain direction, and determine which operational and tactical and investigative measures and actions to be taken in further investigation. As an instrument, the polygraph is almost unmistakable, according to which research shows that the accuracy of the polygraph ranges from 85% to 97%, while in our country its accuracy is 92% of cases. Most often, mistakes do not make a polygraph, but a polygraphic examiner, or a person who reads the results of a polygraph. However, there is no doubt that the polygraph has its boundaries and that there is a small part of the error, and yet it should not give the “virtue” of complete infallibility (Bulka, 2012).

Retrieved from Pravni portal:
Bulka, N. (2012). Poligrafsko testiranje. Osijek: Pravni fakultet Osijek.
Milan Žarković, Božidar Banović, Ljubinka Stupar. (2005). Kriminalistika. Smederevska palanka: Visoka škola unutrašnjih poslova.


Author: Marko Kon