How and why Polygraph, narco-analysis tests are performed?

A numerical value is assigned to each response to conclude whether the person is telling the truth, is deceiving, or is uncertain.

By   |  Published: 5th Oct 2020  5:46 pmUpdated: 5th Oct 2020  5:57 pm

Polygraph, narco-analysis tests put a person in a hypnotic state to ‘reduce’ their ability to lie or manipulate. Let’s read about how and why these tests are carried out.

A polygraph test is based on the assumption that physiological responses that are 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, respiration, change in sweat gland activity, 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.

Narco analysis involves the injection of a drug, sodium pentathlon, which induces a hypnotic or sedated state in which the subject’s imagination is neutralized, and they are expected to divulge true information. The drug, referred to as “truth serum” in this context, was used in larger doses as anesthesia during surgery, and is said to have been used during World War II for intelligence operations.

Supreme Court ruling

Supreme Court in 2010 ruled that no lie detector tests should be administered “except on the basis of consent of the accused”. Those who volunteer must have access to a lawyer, and have the physical, emotional, and legal implications of the test explained to them by police and the lawyer, the Court said. It said that the ‘Guidelines for the Administration of Polygraph Test on an Accused’ published by the National Human Rights Commission in 2000, must be strictly followed.

Criticism of Narco-analysis test

Narco-analysis has been criticized on the ground that it is not 100% accurate. It has been found that certain subjects made totally false statements. It is often unsuccessful in eliciting truth as such it should not been used to compare the statement already given to the police before use of drug.

Narco-analysis in India

Narco-analysis is not openly permitted for investigative purposes in most developed and democratic countries. In India, the Narco-analysis test is done by a team comprising of an anesthesiologist, a psychiatrist, a clinical/ forensic psychologist, an audio-videographer, and supporting nursing staff.

The forensic psychologist prepares the report about the revelations.In May 2017, Indrani Mukerjea, who is facing trial for allegedly murdering her daughter Sheena Bora in 2012, had offered to undergo the lie detector test. The CBI refused, saying they already had sufficient evidence against her.

Dr Rajesh Talwar and Dr Nupur Talwar, who were accused of killing their daughter Aarushi and help Hemraj in Noida in 2008, were given polygraph tests. A video of the narco test on their compounder, Krishna, was leaked to the media.


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