The Hindu: Published on 15 September 2025.
Why in News?
The Supreme Court (bench of Justices Vikram Nath, Sanjay Karol and Sandeep Mehta) acquitted a death-row convict in the Kattavellai @ Devakar case and, in the course of that judgment (15 July 2025), issued nation-wide directions to standardise collection, preservation and documentation of DNA evidence because serious procedural failures in that case made the DNA evidence unreliable.
Short background (the story so far):
In 2011 two people were murdered (and one sexual assault alleged) near Suruli Falls, Tamil Nadu. The prosecution’s case relied heavily on DNA reports. The trial and high court convicted and sentenced the accused to death; the Supreme Court, after hearing the appeal, found major defects in the investigation and handling of DNA samples and therefore acquitted the appellant — and used the occasion to lay down uniform procedures for handling DNA evidence.
Why did the Court intervene? (what lapses it uncovered):
The Court found several investigation/forensic lapses in that case, notably:
Unexplained and significant delay in sending biological samples (e.g., vaginal swabs) to the Forensic Science Laboratory (FSL).
Failure to establish a clear, verifiable chain of custody for the samples, leaving open the possibility of contamination, tampering or substitution.
Non-uniformity in practices across police stations and states — no single mandatory format/procedure was being followed by investigating agencies.
Because these procedural defects go to the reliability of the sample itself (not just the lab test), the Court treated them as fatal to relying on the DNA result in that case.
What have earlier Supreme Court rulings said about DNA reliability?
The Court’s new directions build on earlier precedents emphasising two linked points:
DNA profiles are powerful but procedural quality matters. In Anil v. State of Maharashtra (2014) the Court recognised DNA as valid and reliable, but stressed laboratory quality control and procedures.
Poor collection/handling can render DNA evidence inadmissible or unreliable. In Manoj & Ors. v. State of Madhya Pradesh (2022) and Rahul v. State of Delhi (2022) the Court rejected or down-weighted DNA evidence where contamination risk, deterioration, unexplained storage delays, or deficient documentation made the results suspect. The Court has repeatedly held that DNA is “opinion evidence” whose probative value varies with how it was obtained and tested.
What do the new (Kattavellai/Devakar) guidelines mandate?
The Court issued four core directions for all DNA-involved criminal cases (summary below — see the judgment and reporting for full text):
Prompt, documented collection: DNA samples must be collected with due care, packaged swiftly and documented with case identifiers (FIR number/date, sections, investigating officer, police station, serial number). The collection document must carry signatures and designations of the medical professional, the investigating officer, and independent witnesses.
Responsible and time-bound transport: The investigating officer must be responsible for transporting the sample to the designated police station/hospital and ensure the sample reaches the FSL within 48 hours of collection (any delay must be recorded with reasons and preservation efforts).
Sealing/storage control: While samples are stored pending trial/appeal, no package shall be opened, altered or resealed without express authorisation from the trial court (and a statement from a duly qualified/experienced medical professional).
Mandatory Chain-of-Custody Register: From collection until final disposal (conviction/acquittal), a Chain of Custody Register must be maintained, recording every movement of the evidence with counter-signatures and reasons. The register must be appended to trial court records; failure to maintain it makes the Investigating Officer accountable to explain the lapse. The DGs of Police of all states must prepare and circulate sample forms and instructions.
(These are minimum, uniform procedures the Court directed so that DNA evidence is not undermined by avoidable procedural failures.)
Is DNA alone enough to convict?:
Short answer: No — not automatically. The Court restated established principles:
DNA evidence is opinion evidence (admissible under expert-opinion rules) whose probative value depends on the circumstances of collection, preservation, testing and interpretation. If chain of custody or storage integrity is broken, the DNA match loses much of its weight.
The Court has overturned convictions (including death-penalty cases) where DNA evidence could have been contaminated, was from an open area, or was stored in police custody with unexplained delay — i.e., courts will not allow DNA alone to sustain a conviction if the possibility of contamination/tampering is real.
So: a reliable, well-documented DNA match is highly persuasive, but procedural defects may make it insufficient — courts will look for corroboration and unimpeachable forensic procedures before relying on DNA as the lynchpin for conviction.
Immediate and practical implications:
Investigations: Police must overhaul routine practice — standard forms, 48-hour dispatch targets, training on packaging/sealing, and strict Chain of Custody Registers. States’ DGPs have been ordered to circulate standard templates.
Forensic laboratories: FSLs still must maintain quality control in testing; lab competence remains necessary but is not sufficient if the upstream sample handling is flawed.
Trials/appeals: Defence lawyers will scrutinise custody and transit records; prosecutors must be ready to prove unbroken custody and prompt forwarding. Courts may exclude or devalue DNA if documentation is missing.
Systemic change: The directions, if implemented uniformly, reduce wrongful convictions based on tainted evidence and increase accountability (IOs can be made to explain lapses).
Limitations / what the judgment does not (directly) do:
The Court lays down procedural standards; it does not change scientific testing standards for FSLs (those remain the remit of labs and relevant statutory/regulatory frameworks). Implementation depends on state police machinery, resources, training and monitoring.
What should happen next (practical recommendations):
States should issue standard Chain-of-Custody and evidence forms immediately, train investigators and medical staff, and monitor compliance with the 48-hour rule. (The Court directed DGPs to do exactly this.)
Courts and prosecution should treat Chain-of-Custody Registers as sacrosanct trial records and examine them early in proceedings.
Investment in FSL capacity and independent accreditation of labs will complement these procedural steps so lab quality + upstream handling together ensure reliability.
