Forensic Evidence under the Bharatiya Sakshya Adhiniyam, 2023: Scope, Proof, Chain of Custody and Evidentiary Value

Forensic science supplies the courts with material that no witness can give them: what a substance is, whose blood is on a garment, which weapon fired a cartridge, what a deleted file contained. The Adhiniyam admits all of it under a single provision, Section 39, and the Bharatiya Nagarik Suraksha Sanhita now makes forensic examination compulsory for serious offences. What the statutes have not done is remove the difficulty on which most forensic cases actually turn, which is proving that the thing examined is the thing seized.

1. The Statutory Basis

The addition of the words 'or in any other field' matters here more than anywhere else in the Adhiniyam. Section 45 of the Indian Evidence Act listed foreign law, science, art, handwriting and finger impressions, and courts had to stretch the word 'science' to accommodate disciplines that plainly were not contemplated in 1872. Forensic accountancy, voice analysis, cyber forensics, forensic linguistics and toolmark examination all fit comfortably within the residuary field, and the question whether a discipline counts as a 'science' no longer needs to be argued.

Two further provisions do the practical work. Section 45 makes the grounds of an opinion relevant, which is what permits an expert to be examined about his method. Section 40 makes relevant any fact that supports or is inconsistent with an expert opinion, which is what permits the opposing party to put contrary literature, alternative test results and departures from protocol to the witness.

2. What Forensic Science Contributes

The material tendered under these provisions falls into recognisable families, and it is useful to see them together because the same problems of proof attend all of them.

Biological evidence — blood, semen, saliva, hair, tissue, bone. Grouping and DNA profiling establish whether biological material came from a particular person, and serology establishes what the material is. This is the family that produces the strongest identification evidence available.

Chemical and toxicological evidence — narcotic and psychotropic substances, poisons, alcohol, explosives, adulterants. The examination establishes what a substance is and, where relevant, its quantity and purity, which are frequently ingredients of the offence.

Trace evidence — fibres, glass fragments, paint, soil, gunshot residue. Such material rarely identifies an individual, but it establishes contact between persons, objects and places, and is valuable precisely because its transfer is unintentional.

Marks and impressions — fingerprints, footprints, tyre marks, toolmarks, and the striations that connect a bullet to a barrel. Fingerprints are expressly named in Section 39(1); the rest come in under the residuary field.

Questioned documents — handwriting, signatures, typescript, ink and paper analysis, alterations, erasures and indented writing. Handwriting is named in Section 39(1) and is examined separately, because the courts treat it with markedly more caution than other forensic disciplines.

Digital forensics — recovery and analysis of data from computers, phones and storage media, examination of logs, and authentication of records. This family is governed by Section 39(2) as well as Section 39(1), and by a separate and demanding set of rules about proof in Sections 57, 61 and 63.

3. The New Statutory Framework for Collection

The Bharatiya Nagarik Suraksha Sanhita, 2023 made two changes of real practical consequence to the way forensic material is generated, and both bear directly on how such evidence is proved at trial.

The first is compulsory forensic investigation for serious offences. Section 176(3) of the BNSS requires that where an offence is punishable with imprisonment for seven years or more, a forensic expert shall visit the scene of crime to collect forensic evidence, and shall cause the process to be videographed. This converts what was previously a matter of investigative discretion into a statutory obligation, and it produces a contemporaneous visual record of the collection itself.

The second is the audio-video recording of search and seizure under Section 105 of the BNSS. Where a search is recorded, the circumstances in which an article was found and taken into possession become verifiable, and the familiar dispute about whether a recovery was genuine or planted is placed on an entirely different footing.

4. Chain of Custody

This is where forensic cases are won and lost, and the failure has nothing to do with the science. A report identifying a substance as a narcotic proves what the substance examined was. It does not prove that the substance examined is the substance seized from the accused. That connection has to be established by evidence, link by link, and a break anywhere in it destroys the value of the report entirely.

The links that must be proved are the same in every discipline. Seizure — that the article was taken from the place and person alleged, deposed to by the seizing officer and supported where possible by independent witnesses. Sealing — that it was sealed at the spot, with the seal described and a specimen preserved for comparison. Deposit — that it was entered in the record of the police station and kept in secure custody, with the register produced. Transmission — that it moved to the laboratory in the same sealed condition, with the person who carried it examined and the receipt proved. Receipt and storage at the laboratory — that the seals were intact on arrival, matched the specimen, and that the article was stored securely until examined. Examination — that the article examined is the article received, identified by its markings.

The Standing Committee on Home Affairs observed, when examining the Bharatiya Sakshya Bill, that it contained no provision securing the chain of custody of material and digital records collected during investigation. That observation remains accurate. The Adhiniyam says nothing about custody; what it does is make the report relevant, leaving the connection between the report and the accused to be established by ordinary evidence. The gap is addressed in part by the recording requirements in the BNSS, but only in part.

5. Proving a Forensic Report

A forensic report is a document. Producing it does not put its contents in evidence, and the general rule is that the analyst must be examined.

There is an important statutory exception. The criminal procedure legislation provides that the reports of certain classes of government scientific expert — chemical examiners, serologists, chief inspectors of explosives, directors of fingerprint bureaux, and the like — may be used as evidence without the author being called, subject to the court's power to summon and examine him if it thinks fit. Where a report falls within that provision it may be read; where it does not, the author must be produced.

The exception is narrower than is often assumed. It covers specified officers and specified classes of report. A report by a private laboratory, by an expert retained by a party, or by an officer outside the designated categories does not attract it, and such a report proves nothing unless its author gives evidence.

Even where the exception applies, the party against whom the report is used may apply to have the analyst summoned, and the court will ordinarily permit it where the findings are seriously contested. A party who allows a report to go in unexamined and then attacks it in argument is in a poor position, because the points he wishes to make were never put to the person who could have answered them.

6. Class and Individual Characteristics

The single most important distinction in evaluating forensic evidence is between findings that identify a class and findings that identify an individual. The two are constantly conflated, and the difference determines what the evidence is worth.

A class characteristic narrows the field. Blood of a particular group, a fibre of a particular composition, a shoe of a particular size and tread pattern, a blunt weapon of a particular general description — each excludes a great deal but identifies nothing. Its value is corroborative: it is consistent with the prosecution case and inconsistent with an alternative, but it does not point to the accused.

An individual characteristic identifies a single source. A DNA profile at a sufficient number of loci, a fingerprint with adequate matching ridge characteristics, the striations on a bullet fired through a rifled barrel, and the accidental damage marks on a tool — each is treated as unique or nearly so, and evidence of a match is identification rather than consistency.

7. The Recurring Weaknesses

Forensic evidence fails at predictable points, and the same objections recur across disciplines.

Contamination. Biological and trace material is easily transferred. Where samples from the accused and from the scene were handled together, packed together, or examined in the same session without adequate controls, the match may reflect the handling rather than the offence.

Innocent transfer. A fingerprint on a portable article establishes that the accused touched it, not when or why. Fibres on a garment establish contact between the garments, not that the contact occurred during the offence. Where the accused had an innocent occasion for the contact, the finding proves very little.

Inadequate or degraded sample. A partial DNA profile, a smudged print, a deformed bullet or a decomposed viscera sample may support a much weaker conclusion than the report suggests, and the expert should be asked what the condition of the sample permitted him to say.

Departure from protocol. Every discipline has accepted procedures for collection, preservation and examination. A departure does not automatically invalidate the result, but it must be explained, and Section 40 makes the accepted standards relevant so that the departure can be put to the witness.

Absence of controls. A result without a blank, a positive control and a negative control is a result whose reliability cannot be assessed.

Delay. The interval between collection and examination affects biological and chemical material. Where it is substantial and unexplained, the finding is weakened.

8. Forensic Evidence in a Circumstantial Case

Forensic findings are circumstances, and in a case resting on circumstantial evidence they are subject to the same conditions as every other circumstance. Each must be fully established — which means the chain of custody proved, not merely asserted. Each must be consistent only with guilt — which is where innocent transfer defeats a great many findings. And they must form part of a complete chain, which forensic evidence alone almost never does, because it establishes contact or identity of material rather than participation in the offence.

The strongest use of forensic evidence in such a case is negative rather than positive: to exclude an alternative hypothesis. A DNA exclusion, a ballistic mismatch, a chemical result inconsistent with the defence version — each closes off a possibility, and closing off possibilities is precisely what the fourth of the five conditions requires.

9. Illegally Obtained Forensic Material

Where forensic material has been obtained in breach of a procedural requirement, the question arises whether the report is admissible. The general answer in Indian law is that it is, because relevancy and not the manner of collection is the test of admissibility.

The qualification is important and is frequently decisive. Where a special statute makes compliance with a safeguard a condition of the validity of the recovery itself, non-compliance is not a mere irregularity, and the material cannot be relied upon. The narcotics legislation is the standard example, and forensic evidence relating to a substance recovered in breach of the mandatory safeguards will not sustain a conviction however conclusive the chemical analysis.

A separate limitation arises under Article 20(3). Physical and identificatory material — blood, hair, fingerprints, handwriting specimens, voice samples — may be compelled, because furnishing such material is not being a witness against oneself. The results of narco-analysis, polygraph examination and brain mapping may not, because those results convey personal knowledge and amount to testimonial compulsion.

10. The Position Stated Shortly

1. Forensic evidence enters under Section 39, and the residuary words 'or in any other field' now accommodate every recognised discipline without straining the word 'science'.
2. Sections 40 and 45 supply the machinery for testing it — the grounds of the opinion, and facts supporting or contradicting it.
3. Section 176(3) of the BNSS makes forensic examination compulsory for offences punishable with seven years or more, and requires the collection to be videographed.
4. The videograph and the search recording are electronic records, and must be proved under Sections 57, 61 and 63.
5. Chain of custody is the decisive issue, and the Adhiniyam contains no provision securing it — a gap the Standing Committee identified.
6. A report is not evidence merely by production. The analyst must be examined unless the report falls within the statutory exception for specified government scientific experts.
7. Distinguish class from individual characteristics. Most forensic findings establish consistency, not identity, and only a few disciplines identify a single source.
8. Illegality in collection does not exclude, unless a statute makes compliance a condition of the validity of the recovery.

11. Related Topics and Provisions