Scientific Evidence in Criminal Trials


The theory of evolution befits law as well; to be in existence, a law should update itself in tandem with the changing societal needs so as not to impede the systematic progression of civilization. Comprehensively, the concept of judicial activism and legislative amendments has emerged to make the prevailing laws to be in par with the collective spirit of the society. With the advent of technology and its constant advancement, the traditional method of probing a crime is being dominated by scientific techniques. Some of the renowned methods are brain mapping, polygraph, neuroimaging, and narco-analysis. Of the mentioned tests, which are the combined consequence of the interaction between law and science, the narcoanalysis test is one of the effective scientific tools of interrogation, which is used to form evidence.

Though the narcoanalysis test was done for the first time in the Gohdra Carnage case in the year of 2002, it seized attention only after the Aarushi Talwar case and the Mumbai terror attack case; recently, it has thrust into the limelight in the Shraddha Walkar murder case, where the police sought the court’s permission in conducting the test on Aftab Ponnawala as he was allegedly misleading the investigation. Though the technique intends to speed up the investigation, its applicability and effectiveness rely on its legality. To ascertain whether or not narcoanalysis and other similar scientific evidence are admissible in court through the eyes of the Indian Evidence Act of 1872, it is a prerequisite to understanding its nature, procedure, and constitutionality.

Scientific Evidence and Its Admissibility

Technology has a prominent role to play in every walk of human life, thus, it has not left the crime investigation untouched. The surge of usage of scientific tools in interrogation to get scientific evidence by conducting scientific tests has eliminated the lassitude in the investigation processes. Scientific evidence, which is often termed forensic evidence, is used to exhibit the hidden clues of the case. The scientific evidence is that knowledge is gained by testing the hypothesized causes by using scientific methods that are accepted by the scientific community. Predominantly, the term evidence encompasses all the statements, documents, video recordings, photos, etc, that are produced in the court, which either substantiate or disprove the allegations. As a judge, who is adjudicating the case has limited knowledge of the methods that are used to create the aforementioned evidence, those are termed as expert evidence since it comes as an opinion from the expert, who gets samples and details from the crime scene, submitted to the court as evidence and later scrutinized by the judge.

The scientific evidence of general kind viz. fingerprint, DNA evidence, voice identification, autopsy report, hair and skin evidence, bullet striation, and so on, falls under the ambit of forensic evidence and is admissible in the court. The identified issue in considering polygraph, narcoanalysis, and related scientific methods of getting evidence is that the statements recorded during these sessions are made under hypnosis or semi-conscious state. The scientific evidence helps the investigation officer to identify the suspect by using the forensic report, which has certain essential details viz. the place of the crime, time of occurrence of the crime, nature of the crime, and even cause of crime that links criminal, victim, and the crime scene. Generally, forensic evidence is renowned for its accuracy; hence, the possibility of wrongful convictions is less.

Section 45 of the Indian Evidence Act of 1872 has reference to expert opinion and places emphasis on circumstances when a court shall seek the opinion of the person, who is skilled in a crucial matter that the court is dealing with. The Section confirms the relevancy of the opinion of the person who is expertise, especially in science, art, fingerprint expression, the identity of handwriting, and foreign law. It is pertinent to note the cases Parat v. Bissessar[1]  and Kanchan Singh v. State of Gujarat,[2] as in these cases, the court has dealt with the two prerequisites of expert evidence, they are

  1. The expert opinion is admissible only in cases where the subject is such that involves technical questions on which it’s difficult for the court to form an opinion.
  2. The person giving the opinion is really an expert as defined in the case of Bal Krishna Das Agarwal v. Radha Devi and Ors,[3] and he is the truthful witness.[4]

Nevertheless, the judiciary itself has pinpointed the situations when the expert opinion abandons its importance, for instance in the case of L.C. Goyal v. Mrs. Suresh Joshi,[5] the Apex court has held that the need for expert opinion vanishes with the potentness of the circumstantial evidence. However, the court could always rely on the opinions of the experts as these people possess knowledge of the streams, which the adjudicator lacks. But, it is noteworthy to comprehend the established fact that convicting a person on the sole reliance on an expert’s testimony is highly unsafe.[6]

Narcoanalysis and Its Evidentiary Value

The term Narcoanalysis was coined by Horseley and has its origin in the Greek word ‘Narko’, which means anesthesia or Torpor. The narco test often called truth serum involves the administration of psychotropic drugs such as sodium pentothal, sodium amytal, and scopolamine as part of the diagnostic and psychotherapeutic technique that makes the person (subject) go through it to get into a semi-conscious state, where he get hypnotized and cannot speaks his own will, can only give answers to the asked questions. The dosage differs in accordance with the age, gender, and health of the subject. The wrong dosage will make the subject go into a coma or cause another similar adverse effect on his/her health. This test is based on the universal principle that a person lies with the help of his imagination and that capacity to imagine will be blocked by the administration of certain barbiturates. Before being subjected to the Narcoanalysis test, the accused must undergo a medical examination.

Upon the clearance of the medical examination, the test is conducted by administering the sodium pentothal into the subject’s body to lower his/her inhibitions in presence of an anesthesiologist, forensic psychologist, psychiatrist, and others; as the drug blocks the imaginative capacity, the subject is left with no option but to tell the facts he/she is aware of. The entire session would be recorded, and the report of the forensic psychologist accompanied by recordings would be taken and used against the accused. Here comes the debate over its legality, as Article 20 (3) bestows citizens with the fundamental right against self-incrimination i.e. the accused has the fundamental right to refuse testification, in other words, no individual is obliged to be a witness against himself/herself. Likewise, Article 21 of the Indian constitution guarantees every Indian citizen the fundamental right to privacy. The scientific method of narcoanalysis used to draw evidence from the suspect is allegedly violative of these fundamental rights.

To the common knowledge confessions which are voluntary, credible, and not made in police custody are admissible in court, yet, narcoanalysis tests lack such legal validity as though it is a kind of confession; it is made under the influence of drugs. But, in cases like Ram Chandra Reddy v. State of Maharashtra,[7] Rajo George v. Suprendient of Police,[8] State of Andhra Pradesh v. Inapuri Padma,[9] and Dinesh Dalmia v. State,[10] the court has held that narcoanalysis, lie-detector, and brain fingerprinting to be valid and intra vires Article 20(3) of Indian Constitution if it is not conducted against the will of the person undergoing it. Another reason why the statements given during narcoanalysis tests are considered to be unreliable is that some of such statements given by subjects are scientifically proven to be false.[11] Though narcoanalysis has been prohibited in many world countries, it has always been a part of the Indian crime investigation system. Some of the notable cases are as follows-

Nithari Serial Killing case

This case got public attention because of its gruesome nature, the primary accused namely Moninder Singh Pandher and his servant Surinder Koli were tried for the heinous crimes of murder, cannibalism, sexual abuse, and attempted necrophilia. So as to find the modus operandi and mens rea of the accused, the Noida police conducted the Narcoanalysis test after getting the consent of the subjects, at the Directorate of the forensic laboratory. During the eight-hour session, the test was designed to probe the crime by letting the accused to confess by asking the right questions and getting answers relevant to the case. During this session, the accused koli admitted that he murdered 9 girls, 5 women, and 2 boys, attempted to have sex with the dead bodies, chopped the dead bodies, ate the organs, and threw the remaining at the back of the bungalow numbered D-5 located at Nithari village. Though the confession was consented to, it was held non-admissible in the court but has helped the investigation.

Arushi Talwar case

It is the famous still-unsolved double murder case, the facts involve the murder of 13 years old Aarushi Talwar and 45 years old Hemraj Banjade, who were found dead with their throat slit. There was an expert opinion that the identical throat cut should have been done by a surgically trained person with a surgical instrument, as both the parents of aarushi was dentist, all under the suspicion that they might be murderers. Thus, the narcoanalysis test was conducted on the talwars and other suspects, but no concrete evidence was recorded.


To conclude, the narcoanalysis test, which belongs to the branch of forensic psychology is certainly the need of the hour. All though there are some complexities pertaining to the procedure and the outcome as discussed by the judiciary in the catena of cases, the necessity of applying such a test in the Indian criminal justice system relies on its accuracy. The test report could be admitted as evidence in court if only the government could develop guidelines on narcoanalysis with a better understanding of its procedural aspect and its impact. Though it is an incontrovertible fact that this test is much softer than the use of third-degree methods, the primary concern giving evidentiary value to the Nacro test report is that with the help of which the police could harass or ill-treat the innocents with the pretext of finding the real culprit. There is a mainstream opinion that after obtaining custody, the police could forcefully make the suspects accept the crime; hence better policy is required to look after the processes as like how the Guidelines for the Administration of Polygraph Test (Lie Detector Test) on the Accused was issued by NHRC in 2000 and was reiterated in Smt. Selvi v. State of Karnataka.[12] Similar regulatory guidelines have to be framed; if at all the narco test could be considered as admissible evidence in court.



[1] 39 Cal 245.

[2] AIR 1979 SC 1011.

[3] AIR 1989 All. 133.

[4] Id at 2.

[5] AIR 1999 SC 2222.

[6] Mohmood v. State of U.P, AIR 1976 SC 69.

[7] 2004 All MR (Cr) 1704.

[8] 2006 (2) KLT 197.

[9] 2008 Cr LJ 4566.

[10] 2006 Cr LJ 2401 Mad.


[12] 2004 (7) Kar Lj 501.

Snegapriya V S

A third-year student of law at Vellore Institute of Technology (VIT School of Law), budding first-generation lawyer cum legal researcher with multiple publications in various web journals and portals on different subject matters of law in issue. Being a zealous-natured person with thoughts enrooted in epistemophilia has boosted my passion for research writings by interpreting diversified legal facets. As a perceptive observer and reader, I pay greater attention to the overlooked legal fields where divergent challenges might arise, that include cyber law, environmental law, consumer law, and several constitutional provisions. Besides, I prioritize construing legal problems with social psychology. My dream and vision are to catch myself as a skilled legal adroit.