Use of lie detectors in Criminal Justice – Analysis, Opinion and Pitfall

Author: Pranesh Raj S


The reason for the existence of the Judiciary system is to serve equal justice to people based on events that happened so far and to question the repudiation of fundamental rights guaranteed to the people by the rules created by the same people for their welfare named law.

The word justice itself means fair and upright behavior or treatment. Justice is the fair solution or treatment given to the people who need it when their rights are infringed or when such people suffer any harm. It must also be ensured if it is served to the right people or not. To stop the infliction of undeserved injustice, some methods are used to find the correct people for whom such justice is to be served. One such method is to use the polygraph machine to identify the truth from false.


A Polygraph is what we popularly call a lie detector. It is a test strategy or a device used to find the credibility of the statement given by a person by way of measuring things like their pulse, respiratory action, behavior, blood pressure, heart rate, etc... It is usually done by or under the supervision of a polygraph examiner by way of asking a set of both issue-related and unrelated questions to record their physiological reactions.

Polygraph examiners prefer their individual scoring method instead of a computer- generated one to avoid machine-made errors as this method involves human feelings. This method is famous all over the world and is used for both interrogating as well as for employment purposes where the work involves great secrecy. This method is used by famous agencies like the FBI, NSA, CIA, LAPD, and Virginia State Police. This test is known as Psychophysiological Detection of Deception (PDD) examination within the US federal government.


India is strict about the treatment of people who are involved in criminal justice as a person involved in civil courts cases may only suffer financial losses which can even be redeemed by the court of its will but a person wrongly punished in criminal cases shall lose his part of life by way of punishments like imprisonment. Criminal cases are punishable only when a person is proved to be guilty beyond a reasonable doubt. India does not consider the results given by polygraph as sole evidence because scientists consider it unreliable. No provisions in the Evidence Act; Criminal Procedure Code or Constitution of India have accepted the results of the polygraph test as admissible. However, police use this method for interrogation in rare cases with the permission of the court.

In 2010, the Supreme Court gave a verdict related to polygraph which includes the order relating to the compulsory consent of the subject involved to conduct a polygraph test and also includes an order not to force someone to have the test involuntarily. This verdict also orders other courts to consider the evidence submitted under the polygraph test as evidence under section 27 of the Indian Evidence Act and direct submission of evidence from the polygraph test as inadmissible.


No physiological reaction was ever recorded for finding the truth from deceptive answers. The result was only provided by the observation of polygraph examiners or the detection of any change in their behavior, blood pressure, pulse, etc… by the computer. If the accused is a person who is truly guilty and properly aware of the test, they can even control their physiological behavior to escape proper justice. So no method is used to find the reliability of the results by polygraph machines.

The reaction of an innocent person who is agitated by the sudden false accusation placed upon him will also be peculiar. The mechanism of polygraph is to record any bizarre physiological changes to the questions asked and if such anomalous changes were found, then the answer is considered deceptive. So such behavior of the innocent people will also be considered fishy and will be considered as fabrication of the truth. When considering the rule of Indian Law which is to punish a person only when proved guilty beyond reasonable doubts this method will naturally be considered as witless. Hence Unreliability and imprecision are the major reasons for the pitfall of this method.


Justice and Rights are always available equally for all people but people with non- injurious intentions are only eligible to be benefitted from it. Truth is not only the reality but is also a fable that is beneficial for the welfare of people. Some truths are harmful to the society and some lies are always beneficial for the happiness of society. Polygraph may sometimes help to find the truth which helps the people in need of justice but may also even affect innocent people who may not have done the act of crime with any malicious intentions. Some acts may be morally right and legally wrong and vice versa and the use of polygraph may even affect such morally correct acts. Some truths are better not to be told instead of being communicated.


1) Polygraph testing – EPIC - https://epic.org/privacy/polygraph/

2) How does a lie detector work? - https://science.howstuffworks.com/question123.htm

3) Polygraph testing and its admissibility in court - https://www.lawbulls.in/polygraph-testing-and-its-admissibility-in-court/#:~:text=In%20India%2C%20the%20results%20of,a%20sole%20evidence%20in%20court.&text=Despite%20this%20fact%2C%20polygraph%20is,the%20results%20of%20polygraph%20test.

Edited by J.Shuruthi, Associate editor, Lawgic Stratum.

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