Processing Physical Evidence: Discovery, Recognition and Examination

Link recognition, documentation, recovery and examination. Record original position, collector, method and necessary changes; collection does not close a custody history that continues through storage and analysis.

Select material for a stated investigative question. A visible stain does not identify its biological source, and touch DNA is not visible. Consider controls, background material and alternative explanations.

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.

Every stage can cause irreversible loss. Later photography cannot recreate an altered original scene, and returning later does not guarantee recovery. Avoid unsupported national failure-rate claims.

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:

• Drying is appropriate for many swabs and stained objects, not all biological specimens.
• Keep questioned and known materials separate and change contaminated gloves or tools.
• Document any grouped collection and retain the source relationship; do not mix distinct locations.

Packaging can have primary and protective outer layers. Seal the layers required by the exhibit, hazards and receiving procedure; there is no universal rule that only the outer layer is sealed.

A few class-specific rules to memorise:

• Use breathable packaging for appropriately dried biological objects; liquids need compatible leakproof containers and storage.
• Use bindles, suitable lifts or rigid containers according to trace type; gunshot-residue sampling uses its specific validated kit.
• Use approved vapour-tight packaging for fire debris and volatile samples; suitable cans and specialist bags can also be appropriate.
• Use protective packaging for firearms, fragile objects and sharps after competent safety assessment.
• Network isolation and electrostatic protection serve different purposes; neither is a universal device-handling recipe.

Trapped moisture can promote degradation. The rate depends on the specimen and conditions; avoid a universal hours-to-failure claim or prohibition of all plastic containers for all specimens.

Use appropriate tamper-evident closures and record identifiers and condition. Opening, sampling and resealing should remain traceable under the applicable procedure.

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 submission record identifies the case, exhibits, collection details, hazards and requested questions. Forms, authorisation and seal-reference requirements vary by service; do not assume one national form number.

Record a mismatch or damaged package and follow the laboratory’s discrepancy procedure. Preserve the original condition and seek clarification; rejection, limited acceptance or authorised corrective action depends on the circumstances. Never conceal a discrepancy by replacing the package history.

Custody continues through laboratory receipt, opening, examination, storage and return. Link each report and subsample to its parent exhibit.

Assess biological, chemical, physical and environmental risks before handling. Use trained personnel, suitable procedures and the required protective equipment.

Choose protective measures from the assessed risks and local occupational-safety requirements:

• Use suitable gloves and change them to prevent transfer.
• Select eye, clothing and respiratory protection for the actual splash, particle or inhalation risk.
• Respirator selection, fit and training matter; an N95 does not protect against every gas or vapour.
• Remove and dispose of contaminated protection through the applicable controlled procedure.

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.