There is no crueler tyranny than that which is perpetuated under the shield of law and in the name of justice.”

— Charles de Montesquiesu


Truth is quintessence of justice, which fortifies the citadel of human rights discourse. Revealing the truth behind commission of a crime is an onerous task during investigation proceedings. In various incidents of crime especially in old cases, identifying a criminal and proving guilt beyond reasonable doubt is the greatest challenge. During twentieth century, Polygraph, Narco-analysis and other technologies have emerged as the “Truth machines” to help an investigator to “extract” reality from the subject, especially when conventional methods of investigation and other forensic inputs are rendered ineffective. Deception detectors squarely entail surveillance of psycho-physiological response of the brain while retorting to a query or in a simulated situation. However, these deception detection techniques (DDTs) have globally faced substantial criticism during legal scrutiny across jurisdictions. The Narco-test, being bodily intrusive in nature, has been abandoned in advanced countries.


The Supreme Court of India in Selvi v. State of Karnataka1 has declared procedures under DDTs injurious to Article 20(3) of the Indian Constitution. It also declared any DDT based expert opinion per se having no evidentiary significance. Despite these observations, the highest court has permitted to conduct these procedures only after obtaining consent of the subject. This paradoxical judicial preposition ignites legal discussion even after a decade of the judgment since law enforcement agencies in India have used these techniques in several diabolic offences like the Nithari serial killings (2006)2 and the Arushi-Hem Raj twin murder (2008)3. In high profile scam cases such as the Stamp Paper Scam (2003), and Vyapam scam (2015), these techniques have also been used. News reports have revealed that in the recent Hathras gang rape and murder case, DDTs have been used to divulge “truth” behind the gruesome crime. Hoi polloi in general trust these machines as real fact finder revealing the gospel truth, however in real world, claims to detect deception in oral statements have colossal challenges with limited scope of evidentiary value especially for criminal adjudication. This article delves upon various critical aspects concerning legality and reliability of DDTs in global legal landscape.


Nature of Evidence and Corroboration

Evidences are the wheels to the cart of justice. If justice is the end, evidence is the means. Indeed, evidence has been classified in multiple ways, such as oral evidence (testimony), documentary evidence and material (physical) evidence. Testimony of an ocular witness is considered as sterling evidence; however, it is likely to suffer from multiple limitations like personal vendetta, individual’s perception of a situation, hostility due to duress, intimidation, personal gains, etc. Hence, secondary evidence such as forensic inputs including DDT inputs bring scientific temper in judicial realm by way of corroboration. In courtroom, cross-examination is often described as the “greatest legal engine ever invented for the discovery of truth”,4 however, Criminalistics has emerged as the “modern tech-engine” for discovery of truth transfiguring the criminal trials. Many a times, available evidence may be blurred and investigation necessitates methods to reveal the truth, this led to advent of various deception detectors during oral testimony. However, procedural rectitude for collection of any evidence remains vital for admissibility in courtroom. Global emergence of variety of truth machines has been discussed below.


Polygraph (Lie Detector)

Detecting deception by examining human body is an old age phenomenon.5 Invention of the polygraph may be traced back to 19146 which paved the way in 1921 to devising of an apparatus by John A. Larson, an Australian policeman and psychologist, to measure changes in blood pressure, respiration rate and heart beats in order to aid detection of deception.7 The admissibility of polygraph led to genesis of the Frye8 test in 1923, where US Supreme Court deduced the principle of “general acceptance” in scientific community and rejected the polygraph reports as evidence.9 Leonarde Keeler is credited with creation of the first polygraph testing procedure based on relevant or irrelevant question technique.10 Polygraphs may be classified based on Comparative Question Test (CQT) or Concealed Information Test (CIT) procedures. Polygraph test is conducted in three phases: a pretest interview, chart recording and diagnosis. Based on the answers of known questions, a baseline physiological response is determined and deviation from baseline while replying to critical question is considered as deception or sign of lie.


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DSc (Forensic Sciences and Law). Honorary Professor of National Law University, Delhi and National Forensic Science University, Gandhinagar, India. Serving member of the Indian Police Service in the State of Uttar Pradesh.

†† Candidate of BA, LLB from Jindal Global Law School, Sonipat, India.

*The article has been published with the kind permission of Eastern Book Company. Cite as (2021) 1 SCC J-14

1(2010) 7 SCC 263.

2Surendra Koli v. State of U.P., (2011) 4 SCC 80.

3Rajesh Talwar v. CBI, (2014) 1 SCC 628.

4California v. Green, 1970 SCC OnLine US SC 153 : 26 L.Ed.2d 489 : 399 US 149 (1970), 158 [quoting 5 John Henry Wigmore, Evidence in Trails at Common Law § 1367 (3rd Edn. 1940)].

5 Bennett L. Gershman, “Lie Detection: The Supreme Court’s Polygraph decision”, NY St BJ Sept/Oct 1998 at p. 34. Available at:<>.

6 K. Alder, “A Social History of Untruth: Lie Detection and Trust in Twentieth-Century America”, (2002) 80 (1) Representations 1-33. Also see: John Synnott, David Dietzel and Maria loannou, “A Review of the Polygraph: History, Methods and Current Status”, (2015) 1(1) Crime Psychology Review 59-83.

7 J.A. Larson, G.W. Haney, and L. Keeler, “Lying and its Detection: A Study of Deception and Deception Tests” (Chicago, IL: University of Chicago Press, 1932) p. 99.

8Frye v. United States, 293 F 1013 (DC Cir 1923).

9 The Court of Appeals for the District of Columbia declared that “Numerous cases are cited in support of this rule. Just when a scientific principle or discovery crosses the line between the experimental and demonstrable stages is difficult to define. Somewhere in this twilight zone the evidential force of the principle must be recognized, and while courts will go a long way in admitting expert testimony deduced from a well-recognized scientific principle or discovery, the thing from which the deduction is made must be sufficiently established to have gained general acceptance in the particular field in which it belongs.” Also see: United States v. Scarborough, 43 F 3d 1021, 1026 (6th Cir 1994).

10 L. Keeler, “Deception Tests and the Lie Detector”, International Association for Identification Proceedings, 16, 186-193 (1930).

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