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The Truth of the Truth Test

How accurate and legal are polygraph tests? Aftab Poonawala, accused in the murder of Shraddha Walker, underwent a polygraph test at the forensic science laboratory in Delhi. However, assessments of polygraphy by scientific and  government bodies suggest that the test is an imperfect or invalid means of assessing honesty.
03:28 PM Dec 01, 2022 IST | India Legal
the truth of the truth test

A court recently gave Delhi Police permission to conduct a polygraph test on Aftab Poonawala. The 28-year-old allegedly strangled his live in partner Shraddha Walkar, cut her body into 35 pieces and kept them in a fridge for almost three weeks at his residence in South Delhi’s Mehrauli after which he dumped the body parts across the city over several days. Police say that Poonawala confessed that after chopping the body, he burnt her face to conceal her identity. He also confessed that he had searched on the internet for ways to dispose of the body after murder.

How accurate and legal is a polygraph test? A polygraph is a procedure that measures and records several physiological indicators, such as blood pressure, pulse, respiration and skin conductivity while a person is asked and answers a series of questions. The main motive of a polygraph test is to prove whether a person committed a crime. However, assessments of polygraphy by scientific and government bodies say that it is an imperfect or invalid means of assessing honesty. 

The examiner typically begins polygraph test sessions with a pre-test interview to gain some preparatory information which will later be used to develop diagnostic questions. A polygraph test is conducted on an individual after instruments such as cardio-cuffs or sensitive electrodes are attached to the person and blood pressure, pulse rate, blood flow, etc., are measured to check on the changes in the individual. According to each response that is recorded in numerical value, one comes to the conclusion on whether the person is telling the truth, is misleading, or is uncertain.


A device recording both blood pressure and breathing was invented in 1921 by John Augustus Larson of the University of California and first applied in law enforcement work by the Berkeley Police Department. A device which recorded muscular activity along with changes in blood pressure was developed in 1945 by John E Reid, who claimed that greater accuracy could be obtained by making these recordings at the same time with standard blood pressure-pulse-respiration recordings. A hand-held lie detector is being deployed by the US Department of Defense, according to a report in 2008. The Preliminary Credibility Assessment Screening System, captures less physiological information than a polygraph, and uses an algorithm, not the judgment of a polygraph examiner, to render a decision whether it believes the person is being fraudulent or not. It was first used in Afghanistan by US Army troops.

Some researchers believe that reaction time (RT) based tests may replace polygraphs in secret information detection. RT-based tests differ from polygraphs in impetus presentation duration, and can be conducted without physiological recording, as subject response time is measured through a computer. However, researchers have found restrictions to these tests as subjects voluntarily control their reaction time, deception can still occur within the response deadline, and the test itself records deficient physiological readings. Law enforcement agencies in the United States are by far the biggest users of polygraph technology. Most federal law enforcement agencies in the US, alone either employ their own polygraph examiners or use the services of examiners employed in other agencies. 


It is pertinent to note that the result of polygraph test was used as evidence in a court for the first time in 2008; an Indian court adopted the Brain Electrical Oscillation Signature Profiling test as evidence to convict a woman who was accused of murdering her fiancé. On May 5, 2010, the Supreme Court of India declared the use of narco-analysis, brain mapping and polygraph tests on suspects as illegal and against the Constitution if consent is not obtained. The ruling is significant as probe agencies have used the tests in several high-profile cases. 


The Supreme Court judge, KG Balasubramaniam, in Smt. Selvi vs State of Karnataka held that narco-analysis, polygraph and brain mapping tests were to be allowed only after the consent of the accused. The judge stated: “We hold that no individual should be forcibly subjected to any of the techniques in question, whether in the context of investigation in criminal cases or otherwise. Doing so would amount to an unwarranted intrusion into personal liberty. However, we do leave room for the voluntary administration of the impugned techniques in the context of criminal justice, provided that certain safeguards are in place. Even when the subject has given consent to undergo any of these tests, the test results by themselves cannot be admitted as evidence because the subject does not exercise conscious control over the responses during the administration of the test. However, any information or material that is subsequently discovered with the help of voluntary administered test results can be admitted, in accordance with Section 27 of the Evidence Act, 1872.” 


The National Human Rights Commission had published “Guidelines for the Administration of Polygraph Test (Lie Detector Test) on an Accused” in 2000. These guidelines should be strictly adhered to and similar safeguards should be adopted for conducting the “narcoanalysis technique” and the “brain electrical activation profile” test. The guidelines are:

(i) No lie detector tests should be administered except on the basis of consent of the accused. An option should be given to the accused whether he wishes to avail such a test.


(ii) If the accused volunteers for a lie detector test, he should be given access to a lawyer and the physical, emotional and legal implications of such a test should be explained to him by the police and his lawyer.

(iii) The consent should be recorded before a judicial magistrate.

(iv) During the hearing before the magistrate, the person alleged to have agreed should be duly represented by a lawyer.

(v) At the hearing, the person in question 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.

(vi) The magistrate shall consider all factors relating to the detention, including the length of the detention and the nature of the interrogation.

(vii) The actual recording of the lie detector test shall be done by an independent agency (such as a hospital) and conducted in the presence of a lawyer.

In the case of Ramchandra Ram Reddy vs State of Maharashtra (2004), the petitioner argued that the narco-analysis test is an invasion of the body and thus violates Article 20(3) of the Constitution. The Bombay High Court stated that contrary to the belief, sometimes the test could be used to prove the testifier’s innocence.

In the case of Dinesh Dalmia vs State by Spe (2006), the Madras High Court held that as the accused had not allegedly come forward with the truth, the scientific tests were resorted to by the investigating agency. Such a course does not amount to testimonial compulsion. When there is a hue and cry from the public and human rights activists that the investigating sleuths adopt third decree methods to extract information from the accused, it is high time the investigating agency took recourse to scientific methods of investigation. 

In the case of Sh. Shailender Sharma vs State & Another (2008), the Delhi High Court observed that having regard to the proliferation of crimes against society, it is necessary to keep in mind the necessity of the society at large and the need for a thorough and proper investigation as against individual rights while ensuring that constitutional rights are not infringed. Consequently, in the Court’s opinion, the narco-analysis test does not suffer from any constitutional infirmity as it is a step in aid of investigation and any self-incriminatory statement, if made by the accused, cannot be used or relied upon by the prosecution.

In Rojo George vs Deputy Superintendent of Police (2006), the Kerala High Court held that the ways in which the crime is conducted in present times are more sophisticated and technology-equipped, and therefore, the conventional means of investigating may not necessarily lead to a fair result.

The Mumbai terror attack accused Ajmal Kasab arrested by police was subjected to a narco-analysis test to corroborate all that he had confessed in his interrogation and to get more information about the conspiracy that was being hatched from Pakistani soil. The CBI during narco-tests conducted on the parents of Aarushi—Nupur and Rajesh Talwar—failed to get any concrete clue which could help investigators in solving the murder case of the teenage girl.

Indian Courts have recognised that the scientific tests do not violate the protection given under the Constitution and a narco-analysis test can be conducted if the condition of the case allows. It is always subjected to the question of whether the provisions of Article 20(3) of the Constitution are attracted or not, since it is the only deception detection test that requires the testifier to make statements. Article 20(3) of the Constitution states: “No person accused of any offence shall be compelled to be a witness against himself. Polygraph tests are still legal if the defendant requests one. 

—By Shivam Sharma and India Legal Bureau

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