Chain of custody is the legal keystone of forensic science. Evidence packaged improperly or sealed with unverified closures is subject to immediate defense motions for suppression under evidentiary rules.

1. The Golden Hour of Scene Containment

First responders must establish a dual-perimeter cordon: an Inner Exclusion Zone encompassing all visible physical evidence and transit paths, and an Outer Command Zone housing incident logs and decontamination staging. All personnel entering the inner perimeter must record full identity, entry timestamp, and purpose on physical tamper-evident logs.

2. Packaging Substrate Selection Rules

• Biological Liquids & Bloodstained Items: Never package moist clothing or biological stains in airtight polyethylene bags; rapid bacterial growth degrades DNA. Always use breathable heavy-duty Kraft paper bags and transfer to certified drying cabinets within four hours.
• Arson & Hydrocarbon Residues: Must be sealed in lined airtight unlined metal cans or certified nylon KAPAK vapor-barrier bags to prevent volatile accelerant evaporation.
• Trace Fibers & Hairs: Collect via clean forensic tape lifters mounted directly to clear acetate backings, sealed inside secondary evidence envelopes.