Processing of Evidence Explained - Unit 3 AC 1.3

Physical Evidence Collection and Processing

Physical evidence includes fingerprints, blood, hair, and fibres - basically anything you can physically touch at a crime scene. Thanks to Locard's exchange principle from the early 1900s, we know that material is always being transferred between people and places, which is brilliant news for investigators.

When police arrive at a scene, they establish a common path to prevent contamination from all the different professionals trampling about. SOCOs (Scene of Crime Officers) and CSI teams wear white suits for serious crimes or just gloves and masks for minor ones - they're not trying to leave their own DNA everywhere!

Different evidence needs different collection techniques. Patent fingerprints are visible (like bloody prints), plastic fingerprints leave permanent imprints, but latent prints are invisible and need special powders or chemical dyes to show up. For trace evidence like hairs and fibres, investigators either pick them up individually with tweezers (tedious but thorough) or use the lifting method with tape.

Top Tip: High intensity lights make hairs and fibres glow, making them much easier to spot during collection.

Evidence Transfer, Storage and Analysis

Everything must be labelled and documented when moved - this chain of custody tracking is absolutely vital for court proceedings. Fingerprints get lifted onto cards with specialist tape or photographed and uploaded to IDENT1, the UK's fingerprint database (only containing prints from people who've been through the criminal justice system).

Storage requirements vary massively depending on evidence type. Biological evidence like blood needs cold storage to keep enzymes alive for DNA extraction. Trace evidence gets stored separately to prevent cross-contamination, while hairs need dry environments to avoid mould and decay.

Analysis happens in forensic labs where scientists examine evidence under microscopes. For fingerprints, they look for loops, arches, and whorls - in the UK, they need a 10-point ridge match plus peer review before confirming a match. Fibres get analysed for whether they're natural, synthetic, or manufactured, which can link suspects to crime scenes.

Real Example: Roy Witten was caught for stabbing someone after his fingerprints were found on glass at the scene.

Testimonial Evidence Processing

Testimonial evidence covers anything written or spoken - witness statements, suspect interviews, victim accounts. This works alongside physical evidence to build the complete picture of what happened and when.

Police collect testimonial evidence using cognitive interviews with open-ended questions that help people remember details without leading them towards specific answers. Interviews happen at police stations, keeping witnesses and suspects separate so they can't influence each other's memories.

Everything gets tape recorded and written down, then transferred to the CPS (Crown Prosecution Service) using encrypted systems. Recordings are transcribed (expensive but necessary), and witnesses must sign statements to verify they're genuine.

Admissibility is crucial - evidence gets rejected if it involves hearsay (repeating someone else's story), forced confessions (using threats or violence), or entrapment (tricking suspects into admissions). The Central Park Five case shows how dangerous false confessions can be when five teenagers were wrongly convicted after being interviewed for seven hours without parents present.

Remember: Vulnerable witnesses can give pre-recorded evidence instead of attending court, making the process less traumatic for them.