Processing Physical Evidence: Discovery, Recognition and Examination

You arrived at this stage through Introduction to Crime Scenes, which laid out the four-stage pipeline (recognition → documentation → collection → reconstruction), and through Securing and Documenting the Crime Scene, which closed off the documentation channels. Collection runs after documentation deliberately: moving evidence destroys its in-situ context, so every item must be photographed, sketched and noted before it leaves its position.

Recognition is the SOCO's judgement call that this smudge, this fibre, this shard, this disturbance, counts as evidence. NCRB after-action reviews repeatedly cite recognition as the most common point of failure across Indian crime-scene work. The trained eye sees touch DNA on a doorknob, a single fibre on a victim's collar with the wrong weave, or glass fragments in the suspect's shoe tread. The untrained eye walks past.

Three rules govern recognition discipline:

• Don't collect what you haven't recognised. Random gathering dilutes the chain of custody and gives the defence "why did you collect this?" openings.
• Don't reject what you can't yet identify. If something looks unusual in context, photograph it and decide later. Recognition is not the same as final identification.
• Trust the photographer. A good crime-scene photographer will surface oddities the SOCO walked past; their proof shot is often the first time anyone sees the trace as evidence.

The collection technique depends on the evidence type, the surface it sits on, and how fragile or volatile it is. Improvising costs samples.

A few non-obvious rules:

• Wet samples are dried, not refrigerated. Refrigeration encourages condensation; drying preserves. Once dry, the sample can be refrigerated for transport.
• One item per packet. Multiple items in a single primary container destroys provenance and breeds cross-contamination claims at trial.
• Glove changes between items. Same glove across multiple items = mixed-DNA contamination claim that the defence wins.

Indian forensic practice uses a two-tier packaging standard. The primary container holds the evidence. The secondary container holds the primary container, the case-identifying label, and any additional documentation slip. The tamper-evident seal closes the secondary, not the primary.

A few class-specific rules to memorise:

• Biological evidence: paper, not plastic. A "druggist's fold" of clean paper for trace; a paper bag for clothing and larger items. Plastic traps moisture and breeds bacteria within hours.
• Trace evidence: the druggist's fold. A square of clean paper folded into thirds three times to lock the contents. The standard primary for hair, fibre, gunshot residue, and powder samples.
• Liquid evidence: glass, not plastic. Volatile accelerants leach through plastic and lose mass to evaporation. Gas-tight glass with a Teflon-lined cap is the standard.
• Firearms: rigid box, individual. Each firearm in its own rigid box, with cable-tied stabilisers preventing internal movement. Magazines and rounds packaged separately.
• Digital: anti-static plus Faraday. Anti-static bags prevent ESD damage to internal storage; Faraday isolation prevents remote wipe commands from network or carrier.

The secondary container is sealed with a tamper-evident closure. The classic Indian standard is wax and thread, with the SOCO's personal seal pressed into the wax. The modern replacement is serial-numbered security tape that visibly shows tampering attempts. Most state SOPs now allow either; CFSL is moving toward security tape with photographic proof of the seal at packing time.

Labels carry, at minimum:

• Case crime number
• Investigating officer's name and station
• SOCO / collector's name
• Item number (matching the rough sketch)
• Date and time of collection
• Class of evidence
• Tests requested (mirrors the forwarding memo)

The forwarding memo (Form 95 in many Indian states) is the transmittal document. It carries the IO's signature, an impression of the seal used (so the FSL can verify the seal at receipt), and an itemised list of what's inside. The FSL receipt clerk verifies the seal against the impression on the memo before opening anything.

The handoff from SOCO to FSL formally closes the in-scene chain of custody and opens the lab chain. We unpack the chain itself in Chain of Custody.

Crime scene work is biohazard work first and forensic work second. The SOCO and FSL personnel handle blood, decomposed tissue, sharps and, increasingly, fentanyl-laced samples that pose direct overdose risk on skin contact.

The minimum PPE for any biological scene in Indian SOCO practice:

• Nitrile gloves, double-layered for wet biological scenes, changed between items.
• N-95 mask for any scene with decomposition or visible airborne particulates.
• Disposable coveralls for scenes with significant biological contamination; the suit is sealed in a biohazard bag at scene exit and incinerated.
• Booties over footwear inside the inner cordon, removed at the same boundary.
• Eye protection for any scene with sharps or potential splash.

Sharps protocol: every sharp lifted goes immediately into a rigid puncture-proof container, separately from any other packaging. Glass shards on a scene are mapped, photographed and then collected with tweezers into a rigid container; never gathered by hand.