Unit 4: Collection and Packaging of Evidences at Crime Scene

Physical evidence collection is the operational core of crime scene work: the point at which observed traces are converted into legally admissible exhibits. The value of any exhibit is fixed at the moment of collection, because errors in recovery, packaging, or documentation cannot be corrected later. This unit establishes the standard sequence, the material-specific procedures, and the accountability system that binds them together.

I. Governing Principles of Evidence Handling

Every collection decision rests on a small set of forensic principles that later sections repeatedly invoke.

• Locard's Exchange Principle: every contact leaves a trace — the theoretical justification for searching, since a perpetrator both deposits and removes material.
• Integrity: the exhibit reaching the laboratory must be the same in nature and quantity as when found; contamination, loss, or addition destroys evidential weight.
• Individualisation over class: recovery must preserve features that let an analyst link an item to a single source (a striation, a DNA profile) rather than merely a class (blood type O).
• Priority of the fragile and transient: collect in order of perishability — a wet bloodstain or a latent print degrades faster than a bullet lodged in wood.
• One item, one container, one label: prevents cross-transfer and keeps documentation unambiguous.
• Sequence of processing: photograph and sketch → note position and measurements → collect → package → seal → label → log. No item is lifted before its position is recorded.

II. Collection of Physical Evidence

A. General Method

Collection is the controlled removal of an item from its context using the least destructive technique that preserves its evidential features.

• Tool selection: use clean forceps, gloves, and disposable pipettes; change gloves between items to avoid cross-contamination.
• Control samples: always collect a reference — unstained carpet next to a bloodstain, or soil from an adjacent undisturbed area — so the analyst can distinguish substrate from evidence.
• Quantity: recover the whole item where possible; for bulk traces (soil, glass), collect a representative sample plus controls.

B. Biological Evidence — Blood, Semen, Saliva, Tissue

Biological fluids carry DNA and must be recovered dry and uncontaminated.

• Wet stains: absorb onto sterile cotton swab or lift the whole stained article; air-dry before packaging — never seal wet, as moisture promotes bacterial degradation of DNA.
• Dry stains on movable objects: submit the whole object.
• Dry stains on fixed surfaces: scrape with a sterile blade onto clean paper, or swab with a slightly moistened swab followed by a dry swab (double-swab technique).
• Anti-contamination rule: no talking, coughing, or sneezing over the sample; mask and gloves prevent operator DNA transfer.

C. Firearms and Ballistic Evidence

The goal is to preserve tool-mark striations and residue patterns for comparison.

1. Firearms: unload only after recording the position of the hammer, safety, and chamber; never insert anything into the barrel; tie to a board through the trigger guard.
2. Bullets and cartridge cases: recover with gloved fingers or rubber-tipped forceps — metal tools scratch the very striations used for individualisation. Wrap each separately in soft tissue.

• Gunshot residue (GSR): collect from the suspect's hands using adhesive stubs or dabbing swabs as early as possible, since residue is lost within hours.

D. Trace Evidence — Hair, Fibres, Glass, Paint, Soil

Trace material is small, easily lost, and prone to cross-transfer.

• Hair and fibres: lift with forceps or clean tape; fold into a paper bindle (druggist fold) before placing in an envelope.
• Glass: collect all fragments for physical (jigsaw) fit and refractive-index comparison; sample glass from each pane at a broken window.
• Paint: recover chips down to the substrate to preserve layer sequence; take a control from an undamaged area.
• Soil: sample the surface layer at the questioned spot and at points radiating outward, keeping strata intact.

E. Latent Fingerprints

Prints are developed and lifted to record ridge detail for individualisation.

• Non-porous surfaces: dust with contrasting powder, then lift with transparent tape onto a backing card of opposite colour.
• Porous surfaces (paper): submit intact for laboratory chemical development (ninhydrin, DFO); do not powder.
• Recording: note surface, position, and orientation of the ridge flow before lifting.

F. Documents and Digital Evidence

These carry information content that must not be altered.

• Questioned documents: handle by edges with gloves; never fold, staple, or write on them; place in transparent protective sleeves.
• Digital devices: if powered off, leave off; if on, isolate from networks (Faraday bag) to prevent remote wiping; document the screen state.

G. Impressions — Footwear, Tyre, Tool Marks

Three-dimensional impressions are captured by casting.

• Casting: photograph with oblique lighting and a scale first, then pour dental stone into the impression; allow full cure before lifting.
• Tool marks: recover the whole marked object where possible; otherwise cast with silicone. Never fit a suspect tool into the mark — this creates artefacts.

H. Applications and Limitations

• Application: correct collection enables DNA typing, ballistic matching, and impression comparison in the laboratory.
• Limitation: no laboratory technique can recover evidential value lost through poor collection; degraded or contaminated samples yield inconclusive or misleading results.

III. Packaging of Physical Evidence

A. General Principles

Packaging protects the exhibit from loss, damage, and contamination during transit and storage.

• One item per package: prevents abrasion and cross-transfer.
• Immobilisation: fix rigid items so they cannot shift and rub during transport.
• Correct medium: match the container to the material — the breathing requirement of biological items opposes the sealing requirement of volatiles.

B. Paper Packaging — Bindles, Envelopes, Bags

Porous, breathable packaging is the default for most dry and biological evidence.

• Bindle (druggist fold): a paper sheet folded in a set sequence to trap hairs, fibres, and small particles without loss through corners.
• Paper bags: for dried bloodstained clothing — paper allows residual moisture to escape, preventing mould.
• Rule: biological evidence is never sealed in plastic, which traps moisture and destroys DNA.

C. Plastic and Airtight Packaging

Reserved for materials that must be sealed from air exchange.

• Arson/accelerant residue: seal in clean, unused metal cans or nylon vapour bags so volatile hydrocarbons cannot evaporate.
• Liquids: leak-proof containers with secondary containment.
• Contrast: plastic preserves volatiles but ruins biological evidence — the packaging choice is dictated by whether the analyte is volatile or biological.

D. Rigid and Specialised Containers

Fragile or sharp items require structural protection.

• Firearms: secured in a box, tied to a board.
• Sharps and glass: rigid puncture-resistant containers to protect handlers.
• Bullets/casings: soft-lined boxes or padded envelopes to preserve striations.

E. Sealing and Labelling

Sealing and labelling convert a package into a tamper-evident, identifiable exhibit.

• Tamper-evident seal: close with evidence tape, then sign or initial across the seal onto the container so any reopening is visible.
• Label content: case number, item number, description, exact location found, date and time, and collector's name/signature.

IV. Forwarding of Evidence to the Laboratory

A. Purpose and Principle

Forwarding transfers exhibits to the analyst while preserving integrity and traceability.

• Forwarding memo/requisition: lists each exhibit, the examination requested (e.g., DNA typing, ballistic comparison), and case details.
• Transport conditions: perishable biological samples forwarded refrigerated or frozen and dispatched promptly; volatiles kept cool and sealed.
• Mode: hand delivery by an authorised officer, or sealed dispatch with tracking; the transfer is logged at both dispatch and receipt.

B. Reception at the Laboratory

• Verification: laboratory checks that seals are intact and package descriptions match the memo before accepting custody.
• Rejection: broken seals or mismatched descriptions can render an exhibit inadmissible.

V. Maintaining Chain of Custody at the Crime Scene

A. Definition and Purpose

Chain of custody is the unbroken, documented record of every person who handled an exhibit and every transfer of it, from discovery to court presentation.

• Purpose: to prove in court that the exhibit analysed is the exhibit found, unaltered.
• Legal effect: any unexplained gap creates reasonable doubt and can lead to exclusion of the evidence.

B. Documentation Requirements

Each custody record must answer who, what, when, where, and why.

• Entries: name and signature of each custodian, date and time of each transfer, and reason for transfer.
• Unique identifier: every exhibit carries a case-plus-item number that appears on the label, the log, and the forwarding memo, tying the three together.

C. Elements That Establish an Unbroken Chain

• Collection record: who recovered the item, and when.
• Sealing and labelling: the tamper-evident seal signed across the closure.
• Transfer log: each hand-over signed by both releasing and receiving parties.
• Storage security: locked, access-controlled evidence room with logged entries between transfers.

D. Significance

• Continuity: demonstrates the exhibit was never unaccounted for.
• Accountability: fixes responsibility on a named individual at every stage.
• Admissibility: a complete chain is the precondition for the exhibit's forensic result being accepted as reliable in court.