characteristics of traces

• what are traces

  material that is left behind
• common traces

  hair

  fibres

  glass

  cotton

  pollen
• importance

  they’re easily left behind and it’s unintentional, this can lead to associations between crime scenes

  they also imply source (what’s found) and activity (how has it ended up there)
• source

  does the evidence come from that specific source

  compare the evidence to crime
• activity

  even if the material comes from the source, was the suspect even committing said act

  compare material with findings

  mechanisms= transfer and persistence
• transfer

  evidence is lost

  source to recipetant

  (recall window example)
• modes of transfer

  primary A to B

  secondary A to B to C
• whats fibres

  natural filament

  yarn to textiles

  two types, natural and synthetic
• natural fibres

  animal such as wool

  minerals such as asbestos

  veg such as cotton plant
• synthetic

  acrylic

  polyester
• most common traces

  glass fibres
• laboratory examination

  evidence recovery

  analysis

  comparison

  evaluation

  verification
• 3 methods of evidence recovery

  lifting

  taping

  shaking
• lifting

  searched by eye

  picked by tweezers

  placed in petri dish
• taping

  evidence is covered in tapes

  tapes collected on sheet
• shaking

  item shaken on collecting surface

  everything recovered in petri dish
• stage 1

  optical methods

  naked eye

  light microscope

  more general less destructive
• stage 2

  intermediate instruments

  refractive method index
• stage 3

  advanced instruments

  TLC

  LC electron microscope

  less general more destructive
• intrinsic

  characteristics of the trace itself - physical properties such as colour size texture shape
• extrinsic

  characteristics that result from the interaction between trace and environment- transfer evidence such as the presence of fibres for a suspects clothing on a victims body
• what does the transfer of material depend on

  donor

  recipient

  area of contact

  duration of contact

  number of contact

  pressure of contact
• what does persistence depend on

  donor

  recipeint

  time since depostion
• physicochemical characteristics of fibres

  shape

  colour

  type
• what is glass

  hard brittle transparent, used to make windows, drinking containers and other articles
• structure of glass

  silica (silicon dioxide) sodium oxide, calcium oxide

  two types of silica - glass (amorphorous) and quartz (regular and uniform)
• manufacture glass

  flat glass - all melted together in a furnace

  container glass - molten glass is placed on the end of a blowpipe and inflated into a mold
• optical methods - fibres

  polarised light microscopy
• optical methods - glass

  physical fit

  interferometry
• instrumental methods - fibres

  micro spec
• instrumental methods - glass evidence

  scanning electron microscope