Guilty knowledge test (lie detector)

This test described in the previous chapter reduces the possibility of the errors I just mentioned. However, in order to use this technique, the verifier must possess such information about the crime that only the truly guilty person has. Suppose, how much money was stolen and in which banknotes, only the employer, the thief and the detector operator know. In this case, when testing a suspect, they will ask: “If you stole money from the cash register, then you know how much was taken. How much: 150? 350? 550? 750? 950 and “The stolen money was in banknotes of the same denomination. If you took the money, then you know exactly what it was banknotes: 5 dollars? ten? 20? 50? 100?
“An innocent person has one chance out of five for a more emotional reaction to the correct answer from the first row, and one chance out of twenty-five for a more emotional reaction if two questions are presented to him, and one chance out of ten million in the case of ten such questions” ^{[ 140]} .
“The important psychological difference between the guilty and the innocent suspects is that the former was present at the crime scene and knows what happened there; images that are inaccessible to the innocent are stored in his mind ... And thanks to this knowledge, the perpetrator recognizes objects and events related to the crime, as well as those who participated in it ... Such identification provokes and excites him ” ^[141] .
The only limitation of this test is that it can not always be used even in criminal investigations. Information about a crime is widely known through publications, and an innocent person sometimes knows everything connected with a crime as well as the guilty one. Even if the newspapers do not disclose information, the police themselves often do so during interrogation. In addition, some crimes in themselves do not allow the use of this technique. For example, it would be difficult to assess the sincerity of a person who, having confessed to a crime, falsely claims that he committed it in self-defense. In addition, at times the innocent could himself be present during the commission of a crime and know everything as well as the police.
Reskin, a supporter of the test questions technique, argues that a test for the guilty’s knowledge gives a greater percentage of errors of falsehood: “... It is believed that the criminal must know the details of the crime that are hidden in the questions asked to him. And if he did not pay attention to these details, if he did not have the opportunity to notice them or he was insane at the time of the crime, then this test is not applicable to him ” ^[142] .
The guilty knowledge test also cannot be used if the suspect is one of those people who do not show ANS reactions available to the detector measurements. As I said in the previous chapter, in relation to the behavioral signs of deception, there is a huge amount of individual differences in emotional behavior. There are no signs of emotional excitement, which are inherent in everyone and which show everything equally. It does not matter what is considered - mimicry, gestures, voice, sweating, - some people absolutely do not express their emotions. Previously, I have already stressed that the absence of any kind of reservations does not yet prove the suspect’s veracity, and just as the absence of changes in the activity of the ANS, as measured by the detector, does not yet prove that a person is not agitated.
A test designed to know the culprit, in relation to people who do not show strong changes in the ANS, may be considered useless. True, Lykken says that this happens very rarely. However, it should be noted that too little research has been done to study how often this happens among people suspected of espionage, crimes, etc. People who do not show bright activity of the ANS do not show convincing results when using the test questions technique because they don’t care how to answer control questions and relevant questions.
In addition, when using the test questions and knowledge test of the culprit, medications can play a major role, suppressing ANS activity and generally making the test results inconclusive. This, also the question of whether psychopaths can successfully pass both of these tests, I will consider later when I sum up all the pros and cons.
The conclusion of the BTO, which contains a critical look at the lie detector, proved that both the mentioned techniques are really vulnerable. The test for the guilty usually makes more mistakes of falsehood, and the test using test questions - errors of unbelief of truth. However, even this conclusion is disputed by some detector operators and researchers. And the ambiguity continues to be maintained here partly because of the very small amount of research ^[143] , and partly because of the impossibility of unambiguously assessing the accuracy of the detector. Errors are constantly detected. The main problem here is to establish the truth - to find some way of determining whether a person is lying or not depending on the detector. And if the researcher does not know which of the subjects lies, and who tells the truth, then there is no way to assess the accuracy of the detector.