In Kattavellai @ Devakar v. State of Tamil Nadu (2025), the Supreme Court issued uniform guidelines on handling DNA samples in criminal cases. 

• The Court intervened after finding serious lapses in the chain of custody and delays in forensic analysis, raising concerns about contamination and reliability.

Background of Case

• In the Devakar case (rape, murder, robbery), the samples were delayed in being sent to the Forensic Science Laboratory (FSL).
• The chain of custody was not traceable, creating suspicion of tampering.
• The Court noted the absence of uniform national procedures, despite DNA’s growing role in criminal justice.

Supreme Court Guidelines (2025)

1. Proper Collection & Documentation – DNA samples must be packaged carefully with FIR details, signed by medical professionals, Investigating officers, and independent witnesses.
2. Timely Transport – The IO must ensure delivery to FSL within 48 hours; any delay must be recorded.
3. Storage Protocol – No sample can be opened, resealed, or altered without trial court approval.
4. Chain of Custody Register – Must be maintained till final outcome (conviction/acquittal) and form part of trial court records. IO is accountable for lapses.

Significance of the Ruling

• Ensures uniformity of procedure across states despite “police” being a State subject.
• Reinforces quality, accountability, and transparency in forensic handling.
• Balances investigative needs with fair trial rights, preventing wrongful convictions.

Nature and Value of DNA Evidence

• Definition: DNA encodes genetic information; obtained from blood, semen, saliva, bone, hair, or skin.
• Use in Criminal Trials: Matches between crime-scene samples and suspects establish common biological origin.
• Legal Standing: While a powerful investigative tool, the Court held it is only opinion evidence under Section 45 of the Evidence Act (now Section 39 of Bharatiya Sakshya Adhiniyam, 2023).
• Probative Value: Not substantive evidence; varies case-to-case; must be corroborated and proved scientifically and legally with other evidence. 

Earlier Judicial Observations on DNA Evidence

• Anil v. State of Maharashtra (2014): DNA profile is valid and reliable if proper quality control and lab procedure are ensured.
• Manoj v. State of Madhya Pradesh (2022): DNA report rejected; samples collected from open area and likely contaminated.
• Rahul v. State of Delhi (2022): DNA evidence discarded as samples were kept in police Malkhana for two months, with suspicion of tampering.

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