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Truth detection methods: Its legality and scientific validity

Written by: Abir Chatterjee - I am a student of 5th yr Symbiosis Law College, Pune.
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The advancement of science has led to many great and modern machines and methods. A great number of discoveries and research has led to the overall betterment of human civilization as we know it. Many fields have benefited from major advancements in medical sciences. Man has had an immemorial quest for truth and has been search of various techniques to discover truth. Thus, man has turned to the field of medical science in search of the holy grail of truth detectors. It has so far eluded him but this quest has turned up a few tricks with which the police would be able to apprehend the culprit. Over the past 100 years, there have been many developments regarding the scientific tools for interrogation and investigations. The need for quick methods of discovering truth along with the impatience of man has had a great deal to contribute to this particular field of forensic science.

Sir James Stephens, writing in 1833, rationalizes a grisly example of such impatience of the Indian police, “it is far pleasanter to sit comfortably in the shade, rubbing red pepper in a poor devil’s eyes than, to go about in the sun hunting up evidence.”

The scientific history of lie detection methods can be traced to the early 1900s. As early as 1885, Caesar Lombroso used a device to measure changes in blood pressure for police cases; a device by Vittorio Benussi used to measure breathing and an abandoned project by William Marston used blood pressure and galvanic skin responses. A device recording both blood pressure and galvanic skin response was invented in 1920 by Dr John A Larson of the University of California and first applied in law enforcement by the Berkeley Police Department. This was the first Lie detector or ‘Polygraph’.

The narcoanalysis method during the past was used only by psychiatrists to find out psychological truth which was achieved by using one or two barbiturates such as sodium amytal or scopolamine. The application of this technique for criminal investigation was adopted in the early 1950s. The first successful report of this technique came from the University of Minnesota. The real credit should go to Robert House, who in 1922 first used it on 2 prisoners in the Dallas County jail. His experiment and conclusion attracted wide attention and the idea of ‘truth serum’ is believed to have first appeared in a news report of House’s experiment.

P300 or Brain mapping Test was developed and patented in 1995 by neurologist Dr Lawrence A Farwall, Director and Chief Scientist, ‘Brain Wave Science’, Iowa.

Scientific Basis:
Lie Detector: the lie detector or polygraph test is an examination, which is conducted on the assumption that the body undergoes certain physical changes when under stress. The heart beat increases; blood pressure goes up, breathing rhyme changes, perspiration increases, etc. A baseline for these physiological characteristics is established by asking the subject questions whose answers the investigators know. Deviation from the baseline for truthfulness is taken as a sign for lie. It is conducted by attaching various probes to the body of the person who is interrogated by the expert.

P300 or Brain Mapping Test: in this test, the subject is first interviewed and interrogated to find out whether he is concealing any information. Then sensors are attached to the subject’s head and the person is seated before computer monitor. He is then shown certain images or made to hear certain sounds. The sensors monitor electrical activity in the brain and register P300 waves, which are generated only if the subject has connection with the stimulus. During the test, the subject is not asked any questions.

Narcoanalysis or ‘Truth Serum’ Test: it is conducted by injecting 3 grams of sodium pentothal is dissolved in 300 ml of distilled water and above solution is administered intravenously along with 10% dextrose over a period of three hours with the help of an anaesthetist. The rate of administration is so controlled to drive the suspect slowly into the state of hypnotic trance. The revelations made during the hypnotic trance are recorded both in video and audio formats. The entire procedure is video graphed.

The questions are designed carefully and are repeated persistently in order to reduce ambiguities during interrogation. The report then made by experts is useful in the process of collecting evidence.

Constitutional Imperatives and other Legal Aspects

Position in the United States: the Fifth Amendment of the U.S Constitution provides against self-incrimination, “ No person shall be compelled in any criminal case to be a witness against himself .“

Position in the Great Britain: it is a fundamental principal of the Common Law system that an accused shall not be compelled to discover documents or objects which incriminate him. Position in India: The provisions against self incrimination are provided in the Code of criminal Procedure. But the framers of the constitution decided to incorporate it as a fundamental right. It is embodied in Article 20(3) which reads, “No person accused of any offence shall be compelled to be a witness against himself. “

The constitutionality of the 3 tests has been challenged. A clear exposition on the issue emerged in the case of Ramchandra Ram Reddy and others Vs The State of Maharashtra.

The Bombay High Court upheld the use of all 3 tests. The court also upheld the order given by the Pune Special court allowing the police to conduct narcoanalysis on the accused inn the infamous fake stamp paper scam. It was held that polygraph and P300 tests didn’t involve any statement being made and the statement made under narcoanalysis was not admissible as evidence in court. The court also held that these tests involved minimal body harm.

From all the points of view, it can be said that no such magic potion as ‘truth serum’ exists. From the tests which were conducted, success depends on the skill of the expert who conducts the tests. The success rate has been claimed to be 94 – 97 % by the FSL Bangalore. The constitutionality of the tests has been held valid and will remain till new ground is broken.

Forensic Science in Criminal Investigation and Trial – B.K. Sharma 4th Edition Universal.
N.S. Basu Forensic Science in Criminal Investigation 3rd Edition Asia Law House Hyderabad
Narcoanalysis Test Constitutional Imperatives (
The Hindu – Pseduscience in criminal investigation 2004

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