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Wires attached to the forehead, head, chest and nerves of the hand- all connecting to a device called a lie-detector machine. The machine has a green light and a red light bulb. The investigator starts asking questions to the accused. Whenever the accused lies, the red light is visible- the accused is, thereafter, declared to be a criminal. We can all easily picture this process in our minds; this is what we have commonly seen in movies and dramas. This is, however, far from reality. Neither is this the mechanism to do the lie detector test nor can the person be declared to be a criminal solely based on this test. With the ever-changing world and the advancement of technology, the need for better investigating methods has arisen as criminals have evolved new ways of committing crime. In such a scenario, scientific methods like BEAP Test, Narcoanalysis Test, Polygraph Test, etc. have been used by investigating agencies all over the world and India is no exception. It, however, needs to be noted that such scientific methods are only allowed in India after the permission of the court and the consent of the accused[1].


Polygraph Test, popularly known as the Lie Detector test, is one of the forensic science methods to determine the truth or lies of the accused based on the psychological responses to a question, which are different from the normal responses. “During the polygraph examination, several instruments like cardiographs, pneumographs, cardio-cuffs and sensitive electrodes are attached to the person which gauges their respiration, blood level, blood flow, pulse rate, etc.- based on which the record of the psychological response is prepared. When all the above-mentioned vitals is high or abnormal it is an indication that the person is lying; whereas when these vitals are somewhat normal, it is an indication of the truth. When a person is lying he’ll answer a question reluctantly, whereas when he is saying the truth he will answer immediately, without any hesitation- which will be reflected in the polygraph report. “[2]

There are three prominent polygraph examination techniques:

The relevant-irrelevant (R-I) Technique;

The Control question (CQ) Technique;

Directed Lie control (DLC) Technique;

Of which the control question (CQ) Technique is the most commonly used one. This Test is, however, not as simple in practicality, as it seems to be in theory. Many scientific pieces of research have proved that these Tests are not accurate and there is always a scope for manipulation. All humans are unique and have their distinct way of reacting to a situation. Instead of being triggered by lying or deception, the tests could be triggered by nervousness, anxiety, fear, confusion or other emotions.[3] In the case of Lie Detector Tests, it may happen that the actual accused may have prepared himself enough to deal with the questions and may have practised to keep himself normal so that his lie is not detected- the examiner may not be able to detect deliberate attempts on the part of the person examined to manipulate the result. On the other hand, an innocent may be nervous because of the environment in the investigating room or may have either have distorted memory or loss of memory- which would be shown in the polygraph report and he may be deemed to be the person who committed the alleged crime.

There have been cases in India in which this Lie Detection Technique has been used: The CBI conducted narco-analysis and lie detector tests on the suspects arrested in connection with the alleged rape and murder of a minor girl in Shimla.[4] Delhi Police’s SIT conducted a polygraph test on 6 close aides of Mr Shashi Tharoor, in connection with the murder case of his wife Sunanda Pushkar.[5] The Polygraph test was conducted on the four accused, after obtaining permission from the Court, in a case pertaining to a building material supplier, Suraj Singh, who was found dead at his rented home on 20 December 2019.[6]


The lie detector Tests or the Polygraph Tests are only admissible to be conducted if these are done with the permission of the Court and with the consent of the accused. The statements given in the lie detector tests have limited admissibility- after the court considers the circumstances under which the tests were done and accepts the statements. In addition to this, these statements indicate to the investigating agency whether the suspect is lying in the matter or not and thus, they can channel their investigation accordingly. On conjunctive reading of Article 20(3)[7] of the Indian Constitution and Section 27[8] of the Indian Evidence Act we can say that if the fact of compulsion is proved, the test results will not be admissible as evidence.[9] The compulsory administration of the impugned technique violates the ‘right against self-incrimination’ mentioned under Article 20(3)[10] of the Indian Constitution. The results obtained from the tests bear a testimonial character and they cannot be categorized as material evidence.[11] Also, compulsory administration of these techniques invades the mental privacy of a person and hence, violates one’s Right to Privacy. It has also been ruled by the SC in the case of D.K Basu[12] that involuntary administration of such techniques is cruel, inhuman and degrading treatment in contravention of Article 21[13] or Right to Life and Personal Liberty. The following are the guidelines[14] issued by the National Human Rights Commission in one of its circulars, to be adhered to while conducting any of the scientific tests:

  1. No Lie Detector Test should be administered without the consent of the accused. An Option should be given to the accused as to whether he wishes to avail the test.[15]
  2. If the accused volunteers for the tests, he should be given access to a lawyer. The police and the lawyer should explain the physical, emotional and legal implications of such a test to him.[16]
  3. The consent should be recorded before a Judicial Magistrate.[17]
  4. During the hearing before the Magistrate, the accused should be duly represented by a lawyer.[18]
  5. At the hearing, the person should also be told in clear terms that the statement that is made shall not be a ‘confessional’ statement to the Magistrate but will have the status of a statement made to the police.[19]
  6. The Magistrate shall consider all factors relating to the detention including the length of detention and the nature of the interrogation.[20]
  7. The actual recording of the Lie Detector Test shall be done in an independent agency (such as a hospital) and conducted in the presence of a lawyer.[21]
  8. A full medical and factual narration of the manner of information received must be taken on record.[22]
    These guidelines of the Commission were circulated to the Chief Secretaries and DGPs of States as well as Administrators and IGPs of UTs by a letter dated 11 January 2000.


The statements obtained from the Lie Detector Tests have weak evidentiary value as there is always a scope for manipulation. Moreover, the test is conducted with the help of a machine hence, and there is always a scope for inaccuracy and faults. It has been proved in many pieces of research that such tests are inaccurate and hence, it is unsafe to rely upon the statements obtained from these tests for conviction. However, it is helpful for the investigating agencies to get an indication of whether any of the suspects are lying or not and hence, they could continue with their investigation accordingly.

Author(s) Name: Mahi Ghai (Panjab University, Chandigarh)


[1]  Selvi & Ors. v State of Karnataka & Anr. (2010) AIR SC 1974

[2] Ibid

[3] Ibid

[4] ‘CBI puts Kotkhai suspects under lie detection, narco tests’ (The Indian Express, 03 October 2017) <> accessed 21 November 2022

[5] ‘Sunanda Pushkar murder case: Polygraph test conducted on 6 Tharoor aides’ (India Today, 22 June 2015) <> accessed 21 November 2022

[6] ‘UP: Four face polygraph test in bizman Suraj Singh’s death case’ (The Times of India, 10 June 2022) <> accessed 21 November 2022

[7] Constitution of India 1950, art. 20(3)

[8] Indian Evidence Act 1872, s 27

[9] Selvi & Ors. v State of Karnataka & Anr., AIR (2010) SC 1974

[10][10] Constitution of India 1950, art. 20(3)

[11] Ibid

[12] D.K Basu v State of West Bengal (1997) AIR SC 610

[13] Constitution of India 1950, art. 21

[14] ‘Guidelines on Administration of Lie Detector Test’ (National Human Rights Commission India) <,given%20access%20to%20a%20lawyer> accessed 11 October 2022

[15] Ibid

[16] Ibid

[17] Ibid

[18] Ibid

[19] Ibid

[20] Ibid

[21] Ibid

[22] Ibid