Kolkata doctor rape-murder: What is a polygraph test? Explainer
Kolkata rape-murder case: CBI will be conducting a polygraph test on the former principal and four doctors of RG Kar Medical College and Hospital.
The Central Bureau of Investigation (CBI) will conduct a polygraph test on the former principal and four doctors of RG Kar Medical College and Hospital in Kolkata, where the gruesome rape and murder of a trainee doctor took place. According to the police, the four doctors allegedly had dinner with the victim a day before the crime. Follow LIVE updates
This comes as the federal agency had sought permission to conduct a polygraph test on Sanjay Roy, the prime accused in the case, from the Sealdah court. Roy, a civic volunteer with the Kolkata police, was arrested a day later after the rape and murder took place and was handed over to the CBI.
What is a polygraph test?
A polygraph test, also known as a lie detector test, is a procedure that measures and records several physiological indicators, such as blood pressure, pulse, respiration, and skin conductivity, while a person is asked a series of questions. As per the test, the deceptive answers will produce physiological responses that can be differentiated from those associated with non-deceptive answers.
How is a polygraph test conducted?
The polygraph test session begins with a pre-test interview to gather preliminary information, which will later be used to develop diagnostic questions. During this phase, the examiner will go over the test questions with the examinee and familiarise him or her with the test process.
After this, a ‘stim test’ is conducted, in which the subject is asked to lie deliberately, and the tester reports that he was able to detect this lie.
Also read: Kolkata horror: CBI status report says crime scene altered; Bengal Police told parents it was suicide then murder
The actual polygraph test starts after this, when the investigator gives and collects many polygraph charts throughout the chart collection phase. The series of questions and charts will differ depending on the number of topics and techniques used. The subject passes the test if the physiological responses to the diagnostic questions are larger than those to the relevant questions.
Are polygraph tests accurate?
The polygraph tests are not scientifically proven to have a complete success rate as the scientific and government bodies generally suggest that the tests are often inaccurate and are an imperfect or invalid means of assessing truthfulness.
While the guilty subjects are likely to become more anxious when they are reminded of the test's validity, there are risks of innocent subjects being equally or more anxious than the guilty.
The result of a polygraph test is not considered a “confession” and is not admissible in a court of law. The tests are done only to assist investigators in their probes and obtain leads from suspects.