OCR AAQ Applied Science • F185 • Lesson 6 • Task 1 preparation

Trace Evidence: Hair, Fibres, Paint and Soil

The tiny materials that make Locard useful — and how to compare them without claiming they uniquely identify a person.

▶ National Forensic Science Week – Trace Evidence (3 min)📖 CSI: Forensic Soil Analysis activity
By the end

You should be able to…

  • describe useful observable features of hair, fibres, paint and soil
  • explain why simple trace comparisons usually provide class evidence
  • select sensible observational comparisons for trace samples
  • write cautious questioned-reference conclusions
Why can a tiny fibre matter in a forensic investigation?
Trace evidence

What can we actually compare?

Click each information panel. It opens straight to the information — no extra reveal.

🧑‍🦱HairColour, diameter and visible cuticle/cortex/medulla features.Click for information
🧵FibresColour, type, diameter, structure or weave.Click for information
🎨PaintColour, layers, texture and particle appearance.Click for information
🌱Soil / dustColour, texture, particles and later microbial evidence.Click for information
Simplified hair shaft Cuticle = outer surfaceCortex = main bodyMedulla = centre
Key misconception: hair structure alone does not normally identify one individual. Treat simple hair/fibre/soil/paint microscopy as comparative class evidence unless a genuinely more discriminating analysis is available.

Questioned vs reference

Use the same feature checklist for the questioned sample and every reference. Record similarities and differences.

Why is “both are red” a weak fibre comparison?
Teacher model

Comparing a questioned hair

Questioned hair: dark brown, similar apparent diameter to Reference A, continuous-looking medulla and smooth overall appearance. B differs in colour/medulla; C differs in diameter/medulla.

Can structure alone prove Reference A is the source?
Guided practice

Which reference is most consistent?

Press start

Work through the cases one at a time.

These are parallel practice examples, not the live set assignment.

Independent consolidation

Trace Evidence Comparison Grid

EvidenceQuestionedReference 1Reference 2
Fibreblue, smooth, ~18 μmblue, smooth, ~19 μmblue, twisted, ~31 μm
Paintred over white layerred over white layersingle red layer
Soildark brown, gritty, pale particlesdark brown, gritty, pale particleslight brown, fine, no pale particles
  1. Identify the most consistent reference for each.
  2. Use at least two features in each justification.
  3. Explain why one result is class evidence.

Review notes

  • Trace evidence includes small transferred materials such as hair, fibres, soil and paint.
  • Hair terminology includes cuticle, cortex, medulla and root.
  • Fibre comparisons can use colour, type/structure, diameter and weave where visible.
  • Paint can be compared using colour, layer structure, texture and particle appearance.
  • Soil can be compared by colour, texture and composition; microbiology can add another layer.
  • Simple school observational comparisons mainly provide class evidence: use 'consistent with' language.

Glossary

Why this matters for Task 1

P2 requires a plan for recovering trace material. P3/M2 require a step-by-step analytical plan and a reason why the chosen observational technique suits each trace type.

Final checkpoint

Lesson 6 quiz