Introduction
Scientific techniques have increasingly been used by investigative agencies to aid criminal investigations. Among these techniques, the polygraph test commonly referred to as a lie detector test has generated significant legal and constitutional debate. While such techniques promise efficiency in uncovering truth, they simultaneously raise serious concerns relating to personal liberty, mental privacy, and the right against self-incrimination.
In India, the constitutional validity of polygraph tests has been questioned primarily in light of Article 20(3), which guarantees protection against self-incrimination, and Article 21, which protects life and personal liberty. This article examines the meaning, procedure, and reliability of polygraph tests and analyses their constitutional position with reference to judicial pronouncements, particularly Selvi v. State of Karnataka.
Meaning And Historical Background Of The Polygraph Test
Historically, attempts to detect deception can be traced back to ancient China, where suspects were made to chew dry rice powder under the belief that fear inhibits salivation. Although scientifically unverified, this method was based on the observation that fear produces physical symptoms.
The first scientific attempt to measure physiological changes associated with deception was made by Cesare Lombroso in 1895, who developed a device known as Lombroso’s Glove to measure changes in blood pressure. Later, in 1947, John Reid, a former police officer and psychologist, refined these techniques, leading to the modern polygraph test.
A polygraph test is based on the principle that deceptive answers produce physiological responses such as changes in blood pressure, pulse rate, respiration, and skin conductivity. These changes are primarily associated with fear of detection rather than guilt itself.
Procedure And Methodology Of The Polygraph Test
The polygraph test is conducted using an instrument that records multiple physiological responses simultaneously. The procedure typically involves:
- Pneumograph tubes attached to the chest and abdomen to record breathing patterns
- A blood pressure cuff to monitor cardiovascular activity
- Electrodes attached to the fingers to measure galvanic skin response
- A motion-sensitive chair to detect bodily movements
The subject is seated comfortably while questions are asked, and physiological responses are recorded in graphical form.
Polygraph Instruments And Functions
| Instrument | Function |
|---|---|
| Pneumograph tubes | Record breathing patterns |
| Blood pressure cuff | Monitor cardiovascular activity |
| Electrodes attached to the fingers | Measure galvanic skin response |
| Motion-sensitive chair | Detect bodily movements |
Essential Requirements For Conducting A Polygraph Test
A polygraph test requires certain basic conditions to ensure reliability and procedural fairness. The two primary essentials are as follows:
Examination Room
The examination room must be a quiet, enclosed, and unfurnished space. It should be free from external noise, visual distractions, and interruptions, as such factors may influence the physiological responses of the subject. Only two individuals should be present in the room during the examination, namely, the examiner and the subject undergoing the test.
Examiner
The role of the examiner is central to the accuracy of the polygraph test. The examiner must be capable of establishing rapport with the subject to ensure cooperation and reduce anxiety unrelated to deception. A qualified and well-trained psychologist is generally considered best suited to conduct a polygraph examination, given the psychological nature of the test.
The examiner must:
- be thoroughly familiar with the facts and circumstances of the case;
- formulate relevant and appropriate questions based on the issues involved; and
- clearly inform the subject about the procedure, technical aspects, nature, and purpose of the test, including any other information necessary to obtain informed consent.
Questioning Techniques Used in Polygraph Tests
Accurate results depend largely on the questioning technique adopted by the examiner. Generally, around 10 questions per chart are asked, with a gap of 10-15 seconds between each question. Yes-or-no questions are preferred due to their clarity over brief questions.
The questions are broadly categorised into:
Types Of Questions In Polygraph Tests
| Category | Description |
|---|---|
| Irrelevant Questions | These questions are unrelated to the crime or investigation and serve as a baseline for normal physiological responses. The Irrelevant questions are those questions which do not have any bearing to the case or the suspect and account for random questions. Relevant questions are usually some or the other way linked to the case and circumstances. |
| Control Questions | These questions relate to situations similar to the offence but are not directly connected to it. They are designed to evoke concern or anxiety and are considered highly reliable for comparison. One to ten control questions are generally asked. |
| Peak Tension Questions | These questions directly relate to the crime and are framed to provoke stress in individuals possessing guilty knowledge. Peak tension questions are framed in such a manner that only one question directly relates to the crime, while the remaining questions gradually approach the critical issue. A person possessing guilty knowledge is likely to exhibit heightened physiological responses when confronted with the relevant question. |
If the subject is unaware of the incident, no significant physiological changes are observed. However, if the subject attempts deception, stress responses are recorded.
Use And Accuracy Of Polygraph Tests
The Central Bureau of Investigation (CBI) has reportedly used polygraph tests during interrogations, claiming an accuracy rate of 90-98%. However, this claim remains contested, as results can be influenced by nervousness, psychological disorders, or deliberate counter-measures.
Due to these limitations, polygraph tests are treated as investigative aids rather than conclusive evidence.
Legal Status of Polygraph Tests in India
In India, polygraph test results are not admissible as evidence in criminal or civil proceedings. There is no explicit provision under the Bharatiya Sakshya Adhiniyam (BSA), Bharatiya Nagarik Suraksha Sanhita (BNSS), or the Constitution governing polygraph tests. Nevertheless, investigative agencies continue to use them as auxiliary tools.
Article 20(3): Right Against Self-Incrimination
Article 20(3) of the Constitution states:
“No person accused of any offence shall be compelled to be a witness against himself.”
The Supreme Court has consistently held that the right against self-incrimination protects an accused from being forced to provide evidence that may expose them to criminal liability. Compelling an individual to undergo a polygraph test extracts information from their mental processes without volition, thereby amounting to testimonial compulsion. Even though the responses may not be verbal, they are nevertheless communicative in nature and fall within the scope of Article 20(3).
Article 21 and Mental Privacy
Article 21 guarantees the right to life and personal liberty. Through judicial interpretation, the Supreme Court has expanded its scope to include mental privacy and autonomy. In Govind v. State of Madhya Pradesh, (AIR 1975 SC 1378) the Court recognised privacy as an integral component of personal liberty.
Forcing an individual to undergo a polygraph test intrudes into the mental domain by compelling disclosure of thoughts and knowledge stored in the mind. Such intrusion violates mental privacy and bodily autonomy, both of which are integral to the due process requirement under Article 21. The absence of procedural safeguards and informed consent further aggravates this violation.
Selvi v. State of Karnataka (2010)
The constitutional validity of polygraph tests was authoritatively examined in Selvi v. State of Karnataka (2010) 7 SCC 263. The Supreme Court considered whether involuntary administration of scientific techniques such as narcoanalysis, brain mapping, and polygraph tests violates Articles 20(3) and 21.
The Court held that involuntary administration of these techniques amounts to testimonial compulsion and is therefore unconstitutional. It observed that compelling an accused to undergo a polygraph test undermines the right against self-incrimination by extracting personal knowledge without consent. The Court further held that such tests also violate personal liberty and mental privacy under Article 21.
The Court emphasised that such tests amount to testimonial compulsion and consent of the subject is mandatory. Even voluntary results are not substantive evidence. Courts retain discretion to permit such tests based on facts and circumstances.
The judgment also laid down safeguards such as informed consent, medical supervision, and procedural transparency.
Evidentiary Value and Corroboration
Polygraph test results do not constitute conclusive proof. Even information obtained voluntarily must be corroborated by independent evidence. In Sahadevan v. State of Tamil Nadu (2012) 6 SCC 403, the Supreme Court held that extra-judicial confessions are inherently weak and cannot form the sole basis of conviction without corroboration.
Conclusion
Polygraph tests, by their very nature, cannot be regarded as completely reliable indicators of guilt. Physiological responses recorded during the test may arise from fear, anxiety, unfamiliar surroundings, or the stress of the examination process itself, rather than from deception. Consequently, the results of a polygraph test do not, by themselves, establish the guilt or innocence of an individual.
However, when compared to more intrusive techniques such as narcoanalysis which involves the administration of drugs and raises serious concerns regarding bodily integrity and human dignity, polygraph tests are relatively less invasive. When conducted voluntarily and in accordance with constitutional safeguards, polygraph tests can assist investigative agencies by facilitating quicker leads, streamlining investigations, and potentially expediting the trial process.
Importantly, such tests may also aid innocent persons in demonstrating the absence of guilty knowledge during the investigative stage. Therefore, if clear statutory guidelines are formulated and strictly followed, ensuring informed consent, procedural fairness, and judicial oversight, polygraph tests may contribute to the development of a more efficient and balanced criminal justice system without compromising fundamental rights.
Sources Referred
- B.R. Sharma, Forensic Science in Criminal Investigation and Trials.
- B.S. Nabar, Forensic Science in Crime Investigation.
- Govind v. State of Madhya Pradesh, AIR 1975 SC 1378.
- Selvi v. State of Karnataka, (2010) 7 SCC 263.
- Sahadevan v. State of Tamil Nadu, (2012) 6 SCC 403.
Written By: Mahek Saraf – 5th BA LLB, ILS Law College, Pune
