How much weight does forensic and expert evidence carry in a criminal trial?

Question

The prosecution is relying heavily on a forensic lab report and expert opinion in my case. How is such evidence treated by Indian courts? I would like to understand which provision governs this, what it entitles me to, and how long I have before the remedy lapses. I also want to know whether I need a lawyer for this or can do it myself.

MyVakeel Legal Desk · Accepted Answer

In India, the answer to "How much weight does forensic and expert evidence carry in a criminal trial?" turns on Bharatiya Sakshya Adhiniyam 2023, Section 39, Bharatiya Sakshya Adhiniyam 2023, Section 45 and BNSS 2023 s.176. The points below set out the position and then what to do about it, in the order it should be done.

BSA s.39 allows the opinion of a person specially skilled in a field such as forensic science, medicine, ballistics, handwriting or fingerprints to be treated as relevant expert evidence when the facts in issue require scientific or technical assessment.

Under s.45, when an expert's opinion is based on the examination of material such as DNA, chemical analysis or documents, the grounds and data on which the opinion rests are also relevant and can be tested in cross-examination.

BNSS s.176 makes forensic examination and collection of scientific evidence mandatory in offences punishable with seven years or more, requiring the investigating officer to involve a forensic expert at the scene of crime and get videography done.

Expert opinion is not conclusive proof; it is only one piece of evidence that the court weighs along with other material, and a conviction cannot rest solely on an expert report without independent corroboration where the case so demands.

The defence has the right to summon the forensic expert for cross-examination and to challenge the chain of custody, sampling method or qualification of the person who authored the report.

In practice, in this order: 1) Obtain a certified copy of the forensic or expert report at the earliest stage possible; 2) Have a qualified counsel or independent expert review the methodology and chain of custody; 3) Summon the report's author for cross-examination rather than accepting the report on its face; 4) Highlight any gaps in sample collection, sealing or transport during trial arguments.

Timing matters here: Bharatiya Sakshya Adhiniyam 2023, Section 39 works on limitation periods, so a forensic evidence claim that is right on the merits can still fail if it is brought late. You can post the details on the MyVakeel forum for a practising advocate to review, or book a paid consultation with a Bar Council verified lawyer in criminal law.