A polygraph test is based on the assumption that physiological responses (heartbeat, sweating, etc.) triggered when a person is lying are different from the normal state. It is also known as a lie detector test.

The goal of a lie detector is to see if the person is telling the truth or lying when answering certain questions but not to forget that the administration of this test is different from narcoanalysis & brain mapping. The main point of discussion are they legal in India.?

In a recent case, Delhi Police approaches to Court to conduct a polygraph test on Aaftab Poonawala, suspected of killing his partner Shraddha Walker, to help investigators find the missing weapon and other evidence in the murder case.


How Polygraph tests work

A polygraph test is based on the assumption that physiological responses (heartbeat, changes in breathing, sweating, etc.) triggered when a person is lying are different from what they would be otherwise. Instruments like cardio-cuffs or sensitive electrodes are attached to the person, and variables such as blood pressure, pulse, blood flow, etc., are measured as questions are put to them. A numerical value is assigned to each response to conclude whether the person is telling the truth, is deceiving, or is uncertain.

A test such as this is said to have been first done in the 19th century by the Italian criminologist Cesare Lombroso, who used a machine to measure changes in the blood pressure of criminal suspects during interrogation. Similar devices were subsequently created by the American psychologist William Marston in 1914, and by California police officer John Larson in 1921.

Are such tests accurate?

Neither polygraph tests nor narco tests have been proven scientifically to have a 100% success rate, and remain contentious in the medical field as well.

However, recently, investigating agencies have sought to employ these tests in the investigation, and they are sometimes seen as being a “softer alternative” to torture or ‘third degree’ to extract the truth from suspects.

Results of these tests admissible as evidence?

The results of the tests cannot be considered to be “confessions”. However, any information or material subsequently discovered with the help of such a voluntarily-taken test can be admitted as evidence, the Supreme Court said, in ‘Selvi & Ors vs State of Karnataka & Anr’ (2010).

Thus, if an accused reveals the location of a murder weapon in the course of the test, and police later find the weapon at that location, the statement of the accused will not be evidence, but the weapon will be.

The Bench took into consideration international norms on human rights, the right to a fair trial, and the right against self-incrimination under Article 20(3) of the Constitution, as it is feared that a false confession could be obtained at times when a case needs to be solved quickly.

“We must recognize that a forcible intrusion into a person’s mental processes is also an affront to human dignity and liberty, often with grave and long-lasting consequences,” the court said, observing that the state’s plea that the use of such scientific techniques would reduce ‘third-degree’ methods “is a circular line of reasoning since one form of improper behavior is sought to be replaced by another”.

Constitutional & Legal Provisions of polygraph, narcoanalysis test

  • Narco-analysis, brain mapping, and polygraph (lie detector) tests against the will or consent of the accused would be an infringement of Article 20 (3) of the Indian Constitution. 
  • Article 20(3) deals with the right against self-incrimination or the right to remain silent (a common law criminal jurisprudence). This constitutional right states that “no person accused of any offense shall be compelled to be a witness against himself”. 
  • Therefore, subjecting an accused to undergo the polygraph or narcoanalysis test is considered a blatant violation of Art. 20 (3), as the accused is testifying against himself. So, obtaining consent from the accused before conducting such tests is necessary.
  • The application of Narco-analysis involves the prime question concerning judicial matters and also human rights. The test is controversial as it raises issues relating to violating an individual’s rights and freedom. 
  • The courts usually criticize polygraph tests or Narco-analysis as it comprises mental torture violating the right to life under Article 21 right to privacy.


M.P. Sharma v. Satish Chandra (1954)

The Supreme Court stated that since the words used in Article 20(3) were “to be a witness” and not “to appear as a witness”, the protection is extended to compelled evidence obtained outside the Courtroom, no compulsion no violation.

State of Bombay v. Kathikalu (1961)

It must be shown that the accused was forced to make a statement that would likely incriminate him in a court of law. But there has to be compulsion or duress, if the accused confesses without any inducement, threat or promise and voluntarily gives consent, then Art. 20(3) will not apply.

Nandini Sathpathy v. P.L.Dani (1978)

Right to Silence had been provided to the accused by virtue of the pronouncement in this case. It was pleaded that no one can forcibly extract statements from the accused, who has the right to maintain silence during the interrogation in the investigation. By the administration of such polygraph tests etc., forcible intrusion into one’s mind is done, thus violating the legitimacy of the Right to Silence so such tests are not reliable. An accused had a right of silence under Article 20(3) of the Constitution & Section 161 (2) of CrPC. The Supreme Court upheld these pleadings. 






Leave a Comment

Your email address will not be published. Required fields are marked *