Shraddha murder case: Delhi Shraddha murder accused Aftab Poonawala to undergo polygraph test. What is a polygraph test? How is this test done? Can the lie detector be cheated?

TV9 Explained: Aftab's polygraph test, what is this test?  Can anyone lie?

Aftab faces polygraph test

New Delhi: Aftab Amin Poonawala, the accused in Delhi’s Shraddha murder, was scheduled to undergo a narco test on Monday (November 21). But, on this day, the Forensic Science Lab informed that Aftab will have to face the polygraph test before the narco test. Then his medical test will be done, then the narco test will be done. The Forensic Science Lab said that all the tests will be completed within the next 10 days. On this day, the Delhi Police applied for Aftab’s polygraph test in the Delhi High Court. What is this polygraph test? How does this lie detector work? Let’s find out –

Lie detector machine

The lie detector machine was invented 101 years ago, in 1921. This machine was invented by John Augustus Larsen. The purpose was to make criminals confess the truth through the device. In our country polygraph test, narco test or any such test requires court permission. Courts grant this permission depending on the importance of the case. Many terrorists, criminals have been polygraph tested in our country before. Although this test is not particularly important in court, the polygraph test is helpful in obtaining important evidence.

Polygraph test

A polygraph test determines whether a person is lying or telling the truth while answering questions. When someone lies, his heart rate, blood pressure etc. change. A polygraph test captures those physical changes. A polygraph machine usually measures four things – breathing rate, pulse rate, blood pressure and how much sweat is produced.

How does a lie detector device work?

Medical test of concerned person is done before polygraph test. There his normal heart rate, blood pressure, pulse rate etc. are checked. Next, four or six points of the lie detector machine are attached to the person’s chest and fingers. Then he was first asked some simple questions. Then gradually questions are asked regarding the respective crime. While answering these questions, changes in the heart rate, blood pressure, pulse rate, etc. of the person are monitored on the machine screen. When the respondent lies, his heart rate, blood pressure, pulse rate decreases or increases. Sweat begins to accumulate on the forehead or palms. From this it can be understood that the person is lying. Truth be told, all physical activity is normal.

Different signs of a liar

According to forensic science experts, when a person tells a lie, a special signal called P300 is released from his brain. Because of that nervous crisis, his heart rate and blood pressure increased.

Can anyone cheat on a polygraph test?

The lie detector machine measures changes in the human body to detect lies. So if a person can control his heart rate, blood pressure, pulse rate and perspiration, he cannot be caught lying in a polygraph test. But this is why the polygraph test is not completely reliable. But most people don’t have that much control over their bodies.


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