Belgium is one of the few EU countries where police still use lie detectors or polygraph testing, and it is the country where the use of the machines is most prevalent. While their use is defended by police, experts continue to denounce them.
Lie detectors are deployed some 500 times a year, mostly in cases involving sexual violence. Although the test does not have the same value as a regular interrogation and the results alone cannot be seen as evidence for conviction, they can serve to support other evidence or direct the investigation.
The country's Justice Minister Vincent Van Quickenborne on Monday announced a new directive that should streamline the deployment of lie detectors across the country, to ensure all polygraph tests are carried out according to the same rules.
"The polygraph is very often used in cases of sexual violence and intra-family violence. Because these cases often result in one person's word being put against another's, it proves to be a powerful instrument to advance the investigation," Van Quickenborne said during a visit to the polygraph department of the federal judicial police in Brussels.
However, he recognised that a polygraph can never give a complete answer and that results should only "serve as a supporting element in an investigation."
How does the test work?
A polygraph does not detect lies, but rather looks at stress-related changes in the body, from blood pressure to heart rate changes, when a question is posed. Two types of yes/no questions are presented during the test, one of which includes the main question at hand, namely whether the person committed the crime in question.
The other type is a control question to discover more about the person in certain contexts, for example their behaviour towards women and sexual activity. In theory, those who are guilty react more strongly to the first question.
According to Van Quickenborne, the test is right in more than 90% of cases, and there are numerous examples where the lie detector has led to a breakthrough or a confession.
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However, according to expertss, this is mainly due to the intimidating effect the stress has on people rather than the accurateness of the test, Bruno Verschuere, professor of forensic psychology at the University of Amsterdam, told De Standaard.
Others have contested the accuracy of the test, stating that stress reactions can be controlled. For example, by responding more strongly to the control question, which is the case with most innocent people, the test can be circumvented.
Protecting the innocent?
The police, meanwhile, argued that the test is mainly to prove someone's innocence. In 65% of cases, the truth is told, and is able to set an innocent person who is being questioned for a crime free. This is why, in many cases, suspects, victims and witnesses request the test themselves.
However, the intimidating effect the test has can also be a disadvantage if it scares innocent people into showing a strong reaction, Verschuere explained. This is clear in the figures regarding the chance of a false positive result, which is 10 to 23%. This could mean, if 500 innocent people are tested each year, 33 to 76 people would be wrongly labelled as liars.
New directive
The directive launched by Van Quickenborne describes the process that must be followed in detail, as well as the role of the polygraphists, who may undergo the test. It also includes a list of cases in which the polygraph can be used.
The circular also aims to ensure that the rights of the person being subjected to the test are strictly respected. For example, each polygraph test must be audio-visually recorded, and the lawyer is allowed to follow the polygraph test at all times.
Additionally, pregnant women, minors under 16 years of age and people who were deprived of their liberty less than 48 hours ago, will not be subjected to the test.
