Posted on: April 27, 2021 Posted by: admin Comments: 0

Author: Thota Raghavendra, Student at Alliance school of law, Alliance University, Bengaluru.


Crime has been in society since the beginning and it has been evolving with time. Even criminals are evolving with time and opting for new ways of committing crimes. in order to escape from the law, Criminals are getting smarter with time and using smarter and more scientific ways of doing crime. To keep society away from wrongdoers, even the laws and authorities have evolved. One such evolution in the interrogation and investigation process is the polygraph test. Polygraphy test is an instrument that detects when a person tells a lie. This instrument is used in many countries for different purposes. As in India, it is used by police officials, CBI, FSL for interrogating the accused. And it has been great help for them in solving many cases. So, this paper explores this new scientific interrogation/investigation method and how does it work, what are the principles followed by the polygraphy, what are the law and guidelines to conduct this test and what is the legal validity of polygraphy test in Indian courts.


Through the ages the way of investigating a case or interrogating an accused has changed and developed new ways has been adopted by the Police. Crime is one such concept which evolved with the time. The criminal also gained knowledge and started adopted new ways do their jobs. So, even the officials have to adopt new way of investigating and interrogating the crime. One of the ways adopted by the police in investigating and interrogating a case is scientific ways. Here the forensic science came into existence. What is forensic science? “scientific discipline which is directed to the recognition, identification, individualization, and evaluation of physical evidence by the application of the principles and methods of natural sciences for the purpose of administration of criminal justice[1]. In general terms, the reasoning of science used by the courts to determine a case is forensic science.

Forensic science has several divisions in helping the police with their investigation and interrogation process. One such division is the lie-detector division. This division of forensic science deals with polygraphy test. This division can be said has the new addition to forensic science. It helps the police in the process of interrogating a suspect or an accused.


Polygraphy test, also generally knowns as lie-detector test. Polygraphy is an instrument used by police to determine if an individual is speaking truth or lies. This technology may be included in interrogation process in recent decades in India. But this technic used by this instrument has a long history. The technic of one saying truth or not goes way-back to ancient china. In ancient china, people use to make the suspects eat dry rice powder and chew, this is because the people believed that when person is in fear or tensed that person doesn’t produce saliva. So, If the powder remained dry, then he/she is considered guilty. This technic/belief of people may be not that reliable in nature. But it is truth that when a person lies there will be some changes physically like increase in blood pressure, and few visible movements in body. The scientist has developed an instrument which follows this technic and principles of observing changes in a human body. And that instrument is known as polygraphy or lie detector.

The first attempt to make an instrument which can detect lies, was very simple. The first machine was only made in such a way that it only detects the changes in the blood pressure of the person who is being questioned. Later on, there were upgrades or advancements in the machine. A scientist named John Reid, improved the instrument and also gave the technique to do the test in an effective way. After further advancement and upgrades to the polygraphy machine became more versatile and reliable in nature. Right now, polygraphy test is more practical and accurate in detection of lies when compared to other scientific methods.


The test works on a psychological principle known as the psychosomatic interaction. The principle deals with the minor physical changes occur in a human body. The changes are like change in the respiration like heavy breathing, Galvanic skin resistance, change in Blood pressure or pulse rate, Muscular pressure, Finger pulse, change in body temperature. Whenever a person lies or fake a statement, that person will have fear of getting caught and he holds his emotions, which leads a mental disturbance within that person. All these reactions lead to psychological changes in that person’s body.

The instrument (polygraphy/lie detector) records the changes taking place in the body of the suspect/the person who is being questioned. It records the changes like abdominal respiration, Galvanic skin resistance[2], the changes in blood pressure and pulse rate and few other aspects. The new model of polygraphy instrument also records the muscular movement in the body of the subject.

The lie detector instrument is attached to the suspect who is being questioned in the following:

  • To record the changes in respiration patterns of the subject (the suspect who is being questioned), one pneumograph tube is strapped around his chest and other one around his abdomen.
  • A regular blood pressure cuff is attached to his upper arm.
  • Electrodes are attached to his fingers (index or ring finger), through which a weak electric current is passed through to measure the galvanic skin reflex.
  • The body movements and pressure are measured through the chair he/she is sitting on. The chair is designed in such way.

The questioning is done by the polygraphy expert, also addressed as an examiner. During the test the physical changes in the subject are recorded on a chart. The examiner should be given all the information required for questioning the subject. For the better results from the test, there are few aspects which need to be considered. The room where the test is conducted, it should be a quite space. The room should not contain a lot of people. Only the polygraphy expert, the subject and the in-charge of that case should be present in that room. The question asked during the test are simple and brief, which should be responded by saying yes or no by the subject. The polygraphy expert have few questioning technics for better results from the test. Questioning session in a polygraphy is easier than the analyzing the polygraphy chart. Analyzing a polygraphy chart is the difficult part of this job. The examiner analysis the chart and gives the final results. Is the subject saying the truth or not.


The National Human Rights Commission vide letter no. 117/8/97–8 dated 11/01/2000 has issued guidelines regarding administration of Polygraph Test to suspects. These following guidelines are made for a fair way to use the polygraphy test on a subject without violating his human rights.

  • The Lie Detector/Polygraphy Test should be administered with the consent of the subject i.e., the accused. There should be an option given to the subject to be taking a polygraphy test or not.
  • When the subject agreed to the test and gives his consent to conduct a Lie Detector/Polygraphy Test on him, then he should have the knowledge of that test and legal implications of the test. The police and his lawyer should give him the required knowledge about the test.
  • The consent given by the subject must be recorded before a Judicial Magistrate.
  • when the polygraphy results are presenting before the Magistrate during the hearing, the police have to show the court that the accused has agreed for the test. And these paper works are presented by the lawyer Infront of judge.
  • The accused who has been in questioning should also have the knowledge and should know clearly that the words spoken by him during the polygraphy test are just the statements made to police, but not confessions.
  • While the judge considering a polygraphy test he will be considering the facts such as how long the accused been in detention and how was the interrogation conducted.

These guidelines were made by the national human rights commission after a petition by Shri Indra P. Choudhry in the year 1997. The petitioner was taken by police and was traumatized by their treatment and later administered a polygraphy test on him. The polygraphy test was conducted on him with his consent and he was not in his full sense, while he was questioned. Taking all those into consideration, the commission made these guidelines for better way to do this test. As the test is about a human psychological behavior. If the test is not conducted in a correct manner, then the results will be not accurate and can be unfairly used against the accused.


As we already discussed that the polygraphy test is one of the new ways opted by the police in easing the investigation process. The polygraphy test is considered to be a Deception Detection Tests. The DDT also include new methods like narco-analysis and brain-mapping. These new methods are less violent in comparison to the methods like third degree interrogation, the polygraphy test poses no violence against the accused and help more accurately in investigation. But, these new methods (Especially Polygraphy test) of investigation or interrogation are mostly follows the process of extracting the information from the accused, which may go against him. In general words, the accused is providing the information which may be used against him in the court of justice. As we know according to the Article 21(3) of constitution of India, a person cannot be a witness against himself. The results of polygraphy test goes against this law. So, this cannot be taken as an evidence in the court of justice.

The national human rights commission has provided the guidelines to administer the polygraphy test without violating the Article 21 of the Indian constitution, which says the personal liberty and right to privacy. Before these guidelines the polygraphy tests were not conducted in proper way, like the accused was forced to take the test and in fear and the circumstances where the accused was questioned, the test results may have not accurate or genuine and also that process violates an individual’s personal liberty. But, even after the guidelines issued there have been cases that the agencies who conduct the test are following the guidelines provided by NHRC. Also, the scientific community feels that the polygraphy test may not be correct in few cases. Because the accused/subject who is been questioned may not be guilty but in fear of interrogation and atmosphere or on any other reason he may panic and the reading on the chart may get inaccurate results. Which leads to the punishment to an innocent person, who committed no offence.

Smt. Selvi v State of Karnataka

“The results of polygraphs and other lie-detection tests, whether they call for a voluntary response or not, are testimonial because the tests are just inductive evidence of the defendant’s epistemic state. They are evidence that purports to tell us either: (1) that we can or cannot rely on the assertions made by the defendant and for which he has represented himself to be an authority, or (2) what propositions the defendant would assume authority for and would invite reliance upon, were he to testify truthfully.”[3]

So, polygraphy test cannot be considered as an evidence. But according to the Section 45 and 45A of Indian evidence act, 1872. Which says the court can take an opinion from an expert in any field which is required to the case. Things like foreign law, science, art, identity of handwriting, finger impression where the judge has limited knowledge. Then taking an opinion from the expert will be helpful to move on with case. Polygraphy test cannot be considered as an evidence, but the court can consider it as an expert opinion under Sec 45A of evidence act. And also, the polygraphy test can help in moving forward the investigation for the police officials.


Polygraphy test is an instrument that measures a person’s psychological and physical changes in his body when he/she lied. Even though, it has accurate results in detecting when a lie, it violates laws like personal liberty and it cannot be considered as evidence in court of justice. Because one cannot be his own witness. And also, the polygraphy test can be easily manipulated with practice. If the accused is an expert liar and has a good control on his emotions then polygraphy is of no use. But, the results of polygraphy can be taken as opinions by the court. And also, the police can use the results for further investigation of that case.

  • B.S.NABAR, forensic science in crime investigation, (Asia Law House, Hyderabad, 2012).
  • S.B. Math, “Supreme Court judgment on polygraph, narco-analysis & brain-mapping: A boon or a bane”, The Indian Journal of Medical Research (2011).
  • A.D.Mukherjee, “CONSTITUTIONAL AND EVIDENTIARY VALIDITY OF NEW SCIENTIFIC TESTS”, Journal of the Indian Law Institute, 529-542.
  • Legal Admissibility of Narco Analysis And Polygraph Test In India, Legal service india available at: (last visited on 16 april, 2021)
  • Umadethan.B, Forensic medicine for police. (CBS Publisers and Distributors, 2010)

[1] B.S.NABAR, forensic science in crime investigation pg.340, (Asia Law House, Hyderabad, 2012)

[2] Galvanic skin resistance: The skin tells everything our skin gives away a lot of information on how we feel when we’re exposed to emotionally loaded images, videos, events, or other kinds of stimuli both positive and negative. No matter whether we are stressed, nervous, fearful, psyched up, stoked, baffled, or surprised whenever we are emotionally aroused, the electrical conductivity of our skin subtly changes.

[3] AIR 2010 SC 1974

Leave a Comment