Forensic Science: Methods of Evidence Collection

The Fundamentals of Evidence Recovery

Evidence integrity is absolutely crucial - you need to prove that nothing has been added, removed, moved, or destroyed since collection. Think of it like maintaining a perfect chain of custody that judges and juries can trust.

The golden rule is PP1: preserve, protect, identify. Surprisingly, how you preserve evidence matters more than the actual item itself. Get the preservation wrong, and even the most damning evidence becomes useless in court.

Proper labelling requires four essential elements: a detailed description (like "103 white tablets"), the exact location where found ("One Sixth Form College, room 0108, corner of teacher's desk"), the precise date and time of collection, and the collector's name and signature.

Key Point: Evidence integrity means proving nothing has changed from crime scene to courtroom - this is what makes evidence legally admissible.

Packaging Methods That Preserve Evidence

Soft packaging includes brown paper evidence bags and tamper-evident (TE) bags, but choosing the right one matters enormously. For fabric evidence like clothing or bedding, never use plastic bags - mould will destroy your evidence. Instead, use breathable paper bags or special breathable TE bags.

However, even breathable TE bags have limitations. The Metropolitan Police discovered that DNA labs rejected evidence from these bags because the breathable panels could get covered in storage bins, compromising the evidence.

For wet blood on clothing, follow this specific process: place the item in an unsealed plastic TE bag, then put that bag inside a paper bag and seal normally. Mark with UP arrows to keep everything upright and add biohazard tape for safety.

Hard packaging uses cardboard evidence boxes, special weapon/tool boxes (designed to pass the "grain of sand test"), and weapon tubes for longer items.

Remember: The wrong packaging choice can destroy evidence completely - mouldy clothing or contaminated samples are worthless in court.