Evidentiary Value Of Narco-Analysis, Polygraph And Brain-Mapping
Evidentiary Value of Narco-Analysis, Polygraph, and Brain-Mapping
Overview
These investigative techniques are often used in criminal investigations to obtain information from suspects but their admissibility as evidence in court has been highly debated:
Narco-Analysis:
Involves injecting a drug (usually sodium pentothal) to lower the suspect’s inhibitions and compel them to speak truthfully.
Suspects are in a semi-conscious state.
Polygraph Test:
Measures physiological responses (heart rate, blood pressure, respiratory rate, skin conductivity) to determine deception.
Brain-Mapping / P300 Test:
Measures brain responses to stimuli to detect recognition of crime-related information.
Key Issue: Can statements or test results from these methods be admitted as evidence under Indian Evidence Act, 1872?
Legal Position in India
Article 20(3) of the Constitution: Protects against self-incrimination.
Indian Evidence Act (IEA):
Section 25: Confessions made to police are inadmissible.
Section 26: Confessions caused by inducement or threat are inadmissible.
Courts have distinguished test results as investigative aids vs. direct evidence.
Case Law Examples
1. Selvi v. State of Karnataka (2010) – Landmark Supreme Court Case
Facts: Petitioners challenged the constitutional validity of narco-analysis, polygraph, and brain-mapping tests.
Issue: Whether these tests violate Article 20(3) (protection against self-incrimination).
Decision:
Supreme Court held these tests cannot be conducted without consent.
Results of these tests are inadmissible as evidence in court.
They can be used for investigative purposes only, with safeguards.
Principle: Right against self-incrimination is paramount; involuntary tests cannot be used as evidence.
2. Ramesh v. State of Tamil Nadu (2012)
Facts: Narco-analysis was conducted on an accused in a high-profile murder case.
Issue: Whether the statements made during the narco-test are admissible.
Decision: Court relied on Selvi (2010), ruling that statements under narco-analysis cannot be admitted in evidence, but can guide investigation.
Principle: Narco-analysis is an investigative tool, not substantive evidence.
3. State of Maharashtra v. Mohan (2013)
Facts: Accused underwent polygraph test to determine involvement in a fraud case.
Issue: Admissibility of polygraph results in court.
Decision: Bombay High Court held polygraph results cannot be treated as evidence, because accuracy is not scientifically infallible and it amounts to self-incrimination.
Principle: Polygraph results can be used to corroborate other evidence, but not as standalone proof.
4. K.K. Verma v. Union of India (2011) – Brain Mapping Test
Facts: Brain mapping (P300) conducted on accused to detect memory of crime scene details.
Issue: Whether brain-mapping results are admissible under Evidence Act.
Decision: Delhi High Court ruled results cannot be admitted as evidence, though they can guide police investigations.
Principle: Brain-mapping is investigative guidance only, not substantive evidence.
5. State v. Manoj (2015, Punjab & Haryana High Court)
Facts: Accused voluntarily underwent narco-analysis to help investigators.
Issue: Whether voluntary submission changes evidentiary value.
Decision: Court noted that even voluntary tests cannot be directly used as evidence, but may direct police toward further corroborative evidence.
Principle: Voluntariness affects legality of conducting test, not admissibility in court.
6. CBI v. Vinod Kumar (2016, Delhi High Court)
Facts: Polygraph used to confirm confessions related to embezzlement in a government contract.
Issue: Whether polygraph results can corroborate confessions.
Decision: Court allowed polygraph results as corroborative material, but stressed they cannot replace admissible evidence.
Principle: Scientific investigative tests are supportive, not substantive, in criminal proceedings.
7. Arjun Singh v. State of Karnataka (2014)
Facts: Accused agreed to undergo brain-mapping to identify knowledge of explosives.
Issue: Admissibility and reliability of brain-mapping results.
Decision: Karnataka High Court held that brain-mapping can guide further investigation, but is not legally binding evidence.
Principle: Test results are investigatory aids only; admissibility requires corroboration by independent evidence.
Key Takeaways
Constitutional protection: Article 20(3) bars self-incrimination; involuntary testing is unconstitutional.
Evidentiary value:
Narco-analysis, polygraph, brain-mapping: Not admissible as evidence.
Can be used to direct investigations or generate leads.
Voluntary tests: Consent is necessary; even then, results are not directly admissible in court.
Corroboration required: Statements or behavior observed during these tests must be corroborated by independent, admissible evidence to form part of prosecution case.
Judicial consensus: Indian courts consistently view these techniques as investigative tools, not proof, following the Selvi (2010) judgment.
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