Footwear Impression Evidence Flashcards
footwear anatomy
midsole sole- area of she most likely to leave a mark upper toe box toe cap throat tongue quater
the sole
Can be made from a variety of materials:
An understanding of materials and processes is essential
Latex derived rubber – e.g. Vibram
- Vulcanised to increase hardness – Hard wearing
- Environmentally friendly
Polyurethane – Variable air bubble content for shock absorption
Thermoplastic rubber (TPR/TPE) – Rubber/plastic property Various shoe types Fairly hard wearing
PVC – Includes chemicals to prevent stickiness at high temperature
Chemically resistant, but sticky when warm
Ethyl vinyl acetate (EVA) – Excellent shock absorption
Commonly midsole material as foam material
manufacturing
manufactured either by:
Molding processes – Completed sole formed in a mold
Cut processes – Sole is cut from pre-made sheeting material
Completion by combination processes also quite common
sole manufacture- compression molding
compression molding
- material placed into the mould
- mould closed, compressed and heated
- Excess material leaks around the edges – Flashing
- Cycle may take up to 10 minutes in some cases
sole manufacture- injection moulding
- Soling material injected in liquid form into a closed mold
- Air holes allow efflux of trapped air – Characteristic flashing
- Formed soling sometimes directly attached to uppers at the same time as the molding process
footwear mark impressions
Present in up to 60% of crime scenes
Intelligence
Excellent ability to link multiple scenes
Poor ability to identify unknown offender
evidential
footwear mark impressions
Often difficult to locate
Easy to miss
Often overlooked
Recent drive to improve results and awareness
Centre for applied Science and Technology (CAST)
plastic 3D impressions
variable in quality
Dependant upon material texture and stability
- Clay soils (if damp) in particular hold marks very well
May contain contaminants which obscure detail
- Small stones, plant detritus etc.
- Never remove these (unless you can guarantee no harm will come to your mark), but note their presence and location
Longevity variable Rain – Stability depends upon medium Wind – Unlikely to be a big problem in most cases Snow Access to other pedestrians
3D impressions treatment and casting
Treatment
Photography – Scale
Casting
Life size – 1:1 Scale allowing a direct comparison to footwear or a reference mark
Shows very fine detail –
3D impressions casting
Dental Stone
Produces high detail, high strength casts which are cheap
Paraffin Wax – Marks in snow (not UK)
Causes immediate melting of impression
Bubbles
Contraction an issue therefore not 1:1
Sulphur – Marks in snow (not UK) Causes immediate melting of impression Fragile H&S implications Contraction one again an issue
surfaces
types smooth non porous - floor tiles - glass -gloss painted surfaces - laminate floor
smooth porous- some loss of detail due to surface topology
- untreated wood
- emulsion surfaces
other surfaces- variable
- carpet
- patterned/stippled surfaces
marks
Patent or latent
Latent marks may only be visible under certain lighting – Oblique
Consist of a variety of substances Dust, powder, ash, dirt, soil Oils, waxes Water Blood
May be of wet or dry origin
This should inform your treatment of the mark
enhancement
Improve contrast between the medium and the mark
Improves the outcome of identification
Some techniques potentially destructive therefore…
Photograph the mark before enhancement
Consider testing any chemical or powder technique on a small lower quality area of the mark before committing
enhancement techniques
-Chemical
- Powders and suspensions
- Physical Lift
ESLA
Gel Lift
- Alternative light source
Quasar, Crimelite (82L)
chemical enhancement
- Thiocyanates
Iron in soil residue will react to form red/brown colour
Good for wet origin marks - 8-Hydroxyquinoline
Reacts with some metallic ions to produce U.V. luorescence – Aluminium
Wet or dry origin marks - Physical developer
Silver deposited preferentially on waxy materials
-Iodine*
Vapour will cause a yellow/brown colour change in waxy or oily materials
-Bromophenol blue
A pH indicator! Turns from yellow to blue above pH 4.6 – dry origin marks
enhancements for marks in blood
LMG
- Leuco malachite green (LMG)
Colour change to green in presence of blood
enhancements for marks in blood
Luminol/blue star
- Luminol/Blue Star
Production of luminescence visible in darkened area
enhancements for marks in blood
KM
Kastle-Meyer (KM) – Colour change to pink
Peroxidase activity
enhancements for marks in blood
Leuco crystal violet
-Leuco-crystal violet (LCV)
Colour change to violet
enhancements for marks in blood
Acid …
-Acid Yellow 7 – Yellow stain
Acid black 1 – Black Stain
Acid Violet 17 – Violet Stain
-protein stains which responds well to marks in blood giving marked enhancement of contrast
chemical enhancement for blood
Method
Suspected bloodstains first fixed
ensure the mark doesn’t run
Dyed
Covered in absorbent material
Material covered in dye and left for 30 mins
Wash
Dye washed off and dabbed with absorbent
material
powder enhancement
-Provide maximum detail and contrast against surface
-May work well with damp or tacky (wet origin) marks
- An alternative is the use of powder suspensions
Powder/Detergent/Water such as SPR
vacuum metal deposition
- Rarely used for the enhancement footwear marks
- Expensive
- Few chambers available in UK
- Lab only
superglue fuming
- Not commonly used for the enhancement footwear marks due to the practicalities of ‘at scene’ fuming
- May be very effective in some cases
- Generally lab based technique
- Portable fuming apparatus is available but practicality is somewhat limited and there are H&S concerns of producing CA fumes in situ
