Evidence Collection

The forensic value of any analysis is bounded by the integrity of the collection. Sloppy seizure cannot be rescued by sophisticated instrumentation; brilliant analysis is destroyed by a contaminated sample. This chapter covers the seven non-negotiable principles: Locard's exchange, documentation discipline, substrate-aware packaging, chain of custody, scene-search patterns, the panchnama, and first-responder priorities.

1.1Locard's Exchange Principle

Edmond Locard formulated the foundational rule of trace evidence in the early 20th century: when two objects come into contact, there is a mutual exchange of trace material. The exchange is bidirectional and probabilistic — not every contact produces detectable trace, but every contact produces some.

What transfers: textile fibres, hair, dust, soil, paint, glass fragments, blood, sweat, saliva, semen, DNA-bearing skin cells, pollen, gunshot residue, ink, tool-mark residue, biological tissue. What persists depends on the substrate. Embedded fibres in carpet pile last weeks. Loose fibres on a jacket shed within hours of normal wear. Dried blood on porous surfaces lasts indefinitely; on non-porous surfaces, it can be wiped away.

The forensic search strategy follows directly: at every contact-point in a scene, recover transferable trace from the surface; from every suspect, recover trace they may have picked up.

1.2Scene Documentation — Wide to Narrow

Documentation must be complete before anything is moved. Once an item is shifted, its spatial relationship to the rest of the scene is lost forever, and the photographs are the only surviving record.

Wide-angle establishing photographs capture the overall scene with reference markers (north arrow, scale bar, fixed landmarks) showing spatial layout. Mid-range relationship photographs show each evidence item alongside its immediate surroundings. Close-ups with scale record fine detail at near-distance with an L-scale or photographic ruler in the same plane as the item. Measured sketch is a hand drawing showing distances between items relative to fixed references. Timed notes are the contemporaneous record — date, time, photograph numbers, observations.

1.3Substrate-Aware Packaging

The wrong packaging can destroy evidence in days. Choose packaging based on moisture state and material composition.

The cardinal rules: dry first if wet; paper for both wet (post-drying) and dry items; never plastic for biological evidence.

1.4Chain of Custody

Chain of custody is the continuous documented record of who handled the evidence, when, and what they did with it — from the moment of seizure until it appears in court. A typical chain-of-custody form records:

• Who collected the item, when, and where
• Seal number applied at the scene
• Every transfer (date, time, recipient signature, recipient organisation)
• Every analysis performed and by whom
• Every storage location

The court relies on this record to be confident that the evidence in court is the same evidence collected at the scene, unaltered. A break in the chain — an unaccounted period, a missing signature, an unsealed packet — gives defence counsel grounds to argue the evidence may have been tampered with.

Modern hardening: for digital evidence, the SHA-256 hash of the imaged storage device is recorded on the panchnama at seizure and verified at every subsequent analysis. Any defence challenge to whether the analysed image is the seized image is rebutted by showing matching hashes throughout the chain.

1.5Scene Search Patterns

Different scene shapes call for different search strategies.

Grid is best for confined indoor scenes because the orthogonal double-pass (north-south then east-west) ensures every square inch is examined twice from different angles. Spiral suits roughly circular or centred scenes with a clear focus (a body in a clearing). Strip / Line is ideal for large open areas with multiple searchers. Zone / Quadrant divides complex multi-area scenes into manageable units.

1.6The Panchnama

The panchnama is India's witnessed inventory document — prepared at the scene by the investigating officer in the presence of two independent panch witnesses, traditionally drawn from the local community. Under the Bharatiya Nagarik Suraksha Sanhita (BNSS), which replaced the Code of Criminal Procedure in 2024, the panchnama remains the canonical evidentiary document linking the scene to the laboratory.

Required content

1. Each item seized — description, quantity, distinguishing marks
2. Location at the scene (with sketch reference where useful)
3. Condition (wet, dry, damaged, intact)
4. Unique identifier (serial number, model number)
5. Packaging seal number
6. For digital evidence: SHA-256 hash of imaged storage
7. Time of seizure
8. Signatures of two independent panch witnesses, the IO, and (where possible) the accused

A defence counsel will scrutinise the panchnama for any discrepancy. Missing entries, the wrong number of witnesses, an unsealed packet, or a hash mismatch all give grounds to challenge admissibility.

1.7First-Responder Priority

Life-saving priority over evidence preservation is non-negotiable. The sequence:

1. Render emergency medical aid — control bleeding, restore breathing, position the victim safely
2. Call medical (ambulance) and forensic backup simultaneously
3. Secure the scene — perimeter as best as possible while aid is rendered
4. Document any disturbance caused by responders (where the medics walked, what was moved)
5. Photograph and preserve once the medical situation is stabilised

The principle: evidence can be recovered from a partially-disturbed scene if the disturbance is documented; a dead victim cannot be revived if aid is delayed for documentation.