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What is the Difference Between Narco & Polygraph Test? News18 Explains Amid Delhi Murder Probe

By: News Desk

Edited By: Vidushi Sagar


Last Updated: November 17, 2022, 16:35 IST

New Delhi, India

Students from Mumbai's Gurukul Art School pay tribute to Shraddha Walkar, who was allegedly murdered by her boyfriend Aaftab Poonawala in Delhi. (PTI Photo)

Students from Mumbai's Gurukul Art School pay tribute to Shraddha Walkar, who was allegedly murdered by her boyfriend Aaftab Poonawala in Delhi. (PTI Photo)

Delhi Police want to conduct narco and polygraph tests on Aaftab Poonawalla. News18 explains what they are and the difference between them

Delhi Police wants to conduct narco and polygraph tests on Aaftab Amin Poonawala, accused of killing his live-in partner and dumping her body parts in a forest area in south Delhi’s Chhatarpur, reports have said.

A police official told PTI that cops had applied to the court for a narco test and that permission was awaited. But what is a narco and polygraph or ‘lie detector’ test, and what is the difference between them? News18 explains:

What are Narco and Polygraph Tests?

The administration of sodium pentothal, also known as truth serum, is used in narcotics analysis tests. This medication reduces an individual’s self-consciousness, allowing them to speak freely. When a person loses self-consciousness and enters a hypnotic state, the test takes place. Examiners can now question the subject and get genuine responses.

Only a psychologist, investigating officer, or forensic expert is present when this test is administered. According to Telangana Today, it is a viable alternative to other well-known third-degree treatments used by investigating agencies.

A lie detector, also known as a polygraph, is a device that records physiological phenomena such as blood pressure, pulse rate, and respiration of a human subject as he answers questions from an operator; the data is then used to determine whether or not the subject is lying. The lie detector, which has been used in police interrogation and investigation since 1924, is still controversial among psychologists and is not always judicially acceptable, Britannica explains.

What is the Difference Between the Tests & Laws’ Perspective?

While the narco test uses the method of narcotics to alter the consciousness of the person being questioned, the polygraph test relies on the person’s physiological marks to determine the ‘truth’. None of these methods have been scientifically proven to have a 100% success rate, and they are also controversial in the medical field.

The Supreme Court ruled in the Selvi vs State of Karnataka & Anr case (2010) that no lie detector tests should be administered without the accused’s consent. Volunteers must also 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 results of the tests cannot be considered “confessions," but any information or material discovered as a result of such a voluntarily administered test can be admitted as evidence.

The Supreme Court cited Article 20 (3), or the right against self-incrimination, which states that no accused can be forced to testify against himself. In the 1997 case of D.K. Basu vs. State of West Bengal, the Supreme Court ruled that involuntary administration of the polygraph and narcos test constituted cruel, inhuman, and degrading treatment under Article 21 of the Constitution, or the Right to Life and Liberty. It may also violate the Right to Privacy, which is a component of the Right to Life.

The results of these tests are not admissible as evidence under the Indian Evidence Act of 1871.

How are they Conducted?

Narco Test

In a narco test, the subject is only subjected to the test if he or she is medically fit. The hypnotic Sodium Pentothal, also known as Thiopentone, is injected into the subject. The dosage is determined by the patient’s age, gender, and other medical conditions.

The dosage must be precise because the incorrect amount prescribed can result in death or coma. Other precautions must be taken while performing the test. The person is placed in a state where they can only answer specific questions after the drug is injected.

Polygraph Test

According to a report by HowStuffWorks, four to six sensors are attached to a person who is taking a polygraph test. A polygraph is a machine that records multiple (“poly") signals from sensors on a single strip of moving paper (“graph"). Sensors typically record:

-The individual’s breathing rate

-The person’s pulse rate

-The individual’s blood pressure

-The perspiration of a person

-A polygraph will sometimes record arm and leg movement as well.

The questioner asks three or four simple questions to establish the norms for the person’s signals when the polygraph test begins. The polygraph examiner then asks the real questions. All of the person’s signals are recorded on the moving paper throughout the interrogation.

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first published:November 17, 2022, 16:34 IST
last updated:November 17, 2022, 16:35 IST
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