Use of Scientific Methods for Collection of Evidence

By Archit Gupta, National Law Institute University, Bhopal.

The Aarushi-Hemraj Murder Case and Nithari Killings Case has brought into limelight the scientific methods of investigation used in India and across the world. The three of them are lie detector or polygraph test, narco-analysis and brain-mapping. They have been in use for quite a time and their constitutional validity has always been questioned by the human right activist and lawyers.


Out of the three above mentioned methods, narco analysis has been a point of discussion these days. Narco Analysis involving the use of the drug scopolamine on criminals in the United States was first reported in 1922. During and after the war years, United States armed forces and intelligence agencies continued to experiment with the truth drugs and this is still in use by the Central Intelligence· Agency (CIA)[i].

Narco Test refers to the practice of administering barbiturates or certain other chemical substances, most often Pentothal Sodium, to lower a subject’s inhibitions, in the hope that the subject will more freely share information and feelings. A person is able to lie by using his imagination.[ii]

Another type of scientific method which is commonly used is Lie Detector or the Polygraph test. It involves attachment of paraphernalia externally to the body which measure several variables such as the pulse, blood pressure, perspiration rate, etc. The test is based on the presumption that a false statement knowingly made by a person will cause these variables to deviate from their standard levels. The standard levels are determined by asking questions to which the answers are known by the interrogator.[iii]

The brain-mapping test involves interrogating the witness on three kinds of questions, neutral words which are directly related to the case, probe words which attempt to elicit concealed information known by the accused, and target words which include findings relevant to the case of which the suspect is not aware. The test does not expect an oral response from the accused, which is merely expected to listen to the words.[iv]


The Universal Declaration of Human Rights, 1948 under Article 11.1 says, “Everyone charged with the penal offence has the right to be presumed innocent until proved guilty according to law in a public trail at which he has had all guarantees necessary for his defense.”

The privilege of the person against right to self-incrimination thus enables the maintenance of human privacy and observance of civilized principles in the enforcement of criminal justice. It also goes in opposition to the maxim ―Nemo Tenetur se Ipsum Accusare” i.e., No man, not even the accused himself can be forced to answer any question, which may tend to prove him guilty of a crime, he has been accused of.

Clause (3) of Article 20 declares that no person accused of an offence shall be compelled to be a witness against himself. This provision may be stated to consist of the following three components:

  1. It is a right pertaining to a person accused of an offence.
  2. It is a protection against compulsion to be a witness.
  3. It is a protection against such compulsion resulting in his giving evidence against himself.

In M.P. Sharma v Satish Chandra, the Supreme Court has pointed out that the immunity offered by Article 20(3) is available only when the police or other investigating authorities, compel the person to do a volitional act to obtain information. Thus the element of compulsion is present when the person is actually forced to make a certain revelation by the authorities under threat or duress etc[v]. Investigation by definition itself includes all proceedings conducted for the collection of evidence by police officers[vi].

The only event where a confession may be admissible is when they are made before a Magistrate. Before a confession is made before a Magistrate, the Magistrate is to explain to the subject that he is not bound to make such a confession and the Magistrate may only record it if he believes that it is being made voluntarily[vii].

The Criminal Procedure Code of 1973 allows conducting the examination of an accused by a medical practitioner at the request of a police officer. However, he must be arrested on a charge of committing an offence of such a nature and alleged to have been committed under such circumstances that there are reasonable grounds for believing that an examination of his person will afford evidence as to the commission of an offence[viii]. An authorization from the Magistrate may be obtained to the effect that the test may be conducted, which lends more credence to the system, being an independent authorization from a judicial institution. Nevertheless, this is not a legal requirement, and the test may be conducted without such authorization[ix].

The information received during scientific tests may be used in two ways, that is, they may directly be used as evidence in Court in a trial or they may be used merely as clues for investigation. Where the tests involve the making of a statement, they may be directly adduced in evidence, provided they do not amount to a confession because proof of a confession before a police officer or in the custody of a police officer is prohibited[x]. However, if the statements are merely admissions, they may be adduced in evidence[xi]. A third alternative is whereby the statements may be used as proof of the specific knowledge of the accused with regard to those facts, information about which has resulted in subsequent discoveries during the course of the investigation[xii].


The judicial opinion relating to self-incrimination, can best be summarized by the decision of the Bombay High Court in Ramchandra Reddy v. State of Maharashtra[xiii] wherein the Court considered whether a statement can be forcibly taken from the accused by requiring him to undergo a Narco test against his will. A strict reading of Article 20(3) suggested to the Court that it shall apply if the statement is inculpating or incriminating the person making it, which can only be ascertained after the test, is administered.

Thus, the Court held that there was no reason to prevent administration of this test because there were enough protections available under the Indian Evidence Act, Code of Criminal Procedure and under the Constitution to prevent inclusion of any incriminating statement made in the course of the administration of the test. It has been stated, however, that the lie-detector does not directly invade the body, and that the brain-mapping test involves no direct violation of the body in the real sense of the term, but merely touching the physique of the person.

The ambit of protection of the right against self incrimination enshrined under Article 20 (3) has been clearly laid down by the Supreme Court in the case of Nandini Satpathy v. P L Dani[xiv]  Here, disagreeing with the narrow construction of the expression ‘accused of an offence’ by Courts in other cases[xv], the Supreme Court clearly laid down that the protection under Article 20 (3) begins to operate at the pre-trial stage. Hence through this landmark case, the Supreme Court widened the scope of ‘compelled testimony’ under Article 20(3) to not just evidence admitted in Court but also state Compulsion in this context could mean both physical and mental.

A Sessions Court in Faizabad in Uttar Pradesh had accepted the report of a narco-analysis test, stating that it is evidence which can be relied upon, to reject a bail application in respect of a murder case. It was expressly treated as evidence only with respect to the bail application to indicate something of the nature of a prima facie case, and not for proving the statements of the accused against him to convict him[xvi].

It is interesting to note that the Forensic Science Laboratory at Gandhinagar in fact refused to conduct the test on a suspect when he did not give his consent. The Magistrate nevertheless ordered the laboratory to conduct the test. In 2006 however, the Supreme Court stayed the order of a metropolitan judge to conduct narco- analysis[xvii].

The Delhi High Court had held that the narco-analysis test is a step in aid of investigation It forms an important base for further investigation as it may lead to collection of further evidences

The Supreme Court[xviii] held the use of narco analysis, brain-mapping and polygraph tests on accused, suspects and witnesses without their consent as unconstitutional and violation of the ‘right to privacy’. However, if with the help of voluntarily administered test, any material or information is subsequently discovered then it can be admitted under section 27 of the Evidence Act, 1872.


The Indian Legislature has given recognition to scientific tools of investigation like narco analysis in the form of the recent amendment to Section 53 of the Code of Criminal Procedure, in 2005. However, as has been highlighted in the model, there are many prerequisites for narco analysis to become an effective tool of investigation.

The Code of Criminal Procedure in its present form does not provide for these prerequisites especially that of informed consent. In fact no provision in the Code of Criminal Procedure necessitates the consent of the accused before an investigation. Mere recognition under the phrase ‘such other tests’ will not suffice considering the increasing use and relevance of the procedure in the present scene of criminal investigation.

[i] Sriram Lakshmanan, Narco Analysis and some hard facts, Frontline2008

[ii] Mohan Bannur, Misconceptions about narco analysis, 4 Indian journal of Medical Ethics (2007), (last visited Nov 30, 2014)

[iii] People’s Union for Democratic Rights, Narco Analysis, Torture and Democratic Rights (People’s Union for Democratic Rights) (2008)

[iv] Just what is the brain-mapping test?, (last visited Nov 30, 2014)

[v] AIR 1954 SC 300

[vi] §.2(h), Code of Criminal Procedure, 1973

[vii] §164(2), Code of Criminal Procedure, 1973.

[viii] §53, Criminal Procedure Code, 1973.

[ix] This may be done by the Magistrate directing the police to conduct such tests as a component

of his general power to direct investigation of an offence under §156(3), Code of Criminal Procedure, 1973.

[x] §§ 25-26, Indian Evidence Act, 1872

[xi] §17, Indian Evidence Act, 1872 defines admission as a statement, oral or documentary or contained in electronic form which suggests any inference as to any fact in issue or relevant fact.

[xii] §27, Indian Evidence Act, 1872.

[xiii] All MR (Cri) 1704

[xiv] (1978)2 SCC 424

[xv] R.N.Bansilal v. M.P. Mistry, AIR 1961 SC 29; State of Bombay v. Kathi Kalu Oghad, AIR 1962 SC 1808;

R.G.Mehta v. State of West Bengal, AIR 1970 SC 940; Bhagwandas Goenka v. Union of India, Cr.Appeals 131 &

132 of 1961, dated September 20,1963

[xvi] Uttar Pradesh court admits narco report as evidence: India, (last visited Nov 30, 2014)

[xvii] Apex court stays narco-analysis test on Krushi Bank MD The Hindu, (last visited Nov 30, 2014)

[xviii] Selvi & Ors v. State Of Karnataka & Anr, 2010 (7) SCC 263