Trace Evidence: Analysis and Collection

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Trace Evidence
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LOCARDS PRINCIPLE

• Whenever there is contact between two surfaces,
  there is a mutual exchange of materials.

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DestructivevsNon-destructiveTestingMethods
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Properties

• Physical Properties
• Describe a substance without reference to any
  other substance
• e.g. weight (mg), density (m/v), color,
  refractive index, volume, boiling point, melting
  point, etc.

• Chemical Properties
• The behavior of a substance when it reacts or
  combines with another substance.
• e.g. solubility, color tests, spontaneous
  combustion, oxidation

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Classification of Trace Evidence
Class Characteristics No definite identification
possible due to multiple sources or insufficient
characteristics for individualisation Soil,
hairs, fibers, paint, small glass
fragments Individual Characteristics Positively
identified as coming from a particular
source Physical Match e.g. Larger Glass Fragments
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Observation of the physical characteristics

• Physical Match
• Refractive Index
• Artifacts
• Manufacturer Marks
• Damage

• Color
• Size
• Fluorescence
• Morphology
• Diameter

All you need is a microscope!
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The Goal for Examinations
Successfully-

• Identify
• Individualize
• Compare
• Reconstruct
• Report
• Testify

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Trace Analysis Section
Identification and Comparison of

• Hairs
• Fibers
• Paints
• Soil
• Automotive Paint Database
• Clothing Damage

• Fabrics/ Cordage
• Glass
• Plastics / Polymers/ Rubber
• Gunshot Residue
• Light Bulbs
• Tape