marks, impressions and traces

marks and impression - tyres

• fitted to a range of vehicles

• tyre mark data base - 8500

mark and impressions - tread

• show dimensions and a design of individual types

• impression evidence

mark and impressions - visible 2D

• left in substrate

• tyre leaves behind residue/marks on surfaces

mark and impression - impressed

• 3D negative prints - tyre tread impressed into a soft substance

• measurements taken

• cast the marks

• snow wax or hairspray to secure mark in snow

glass

float - windows and doors

toughened - windows and doors

laminate - vehicles

patterned - churches

wire-reinforced - security doors

container - glass bottle

fibres

• fibres are the individual filaments from which textiles are composed

• most textiles will transfer their component fibres when they come into contact

• they are the most frequently encountered type of trace evidence

• natural fibres - derived from plants and animals

• synthetic - produced from polymers

factors affecting transfer

• the amount of pressure at the time of contact

• the length of time the contact occurred for

• how many times contact was made

• the texture of both the do not and recipient garments

recovery of fibres

• photography

• recover whole item if possible

• fibre taping

  Use wide tape – place onto acetate

  All fibres to be on tape, not over the edge – add tape if necessary

  Details to be completed on acetate - bag

  If necessary pull out fibres/tufts

hairs

• photograph as always

• document if there’s a root or not

• individual/clump - use tweezers

recovery of hair from suspect

• for DNA analysis - 3 individual hairs of same type with root

• dor drug analysis - at least 30 hairs with root from the head

paint

• obtain sample from as close to damaged area as possible

• new scalp blade

• control sample from undamaged area

tools

• have a unique marking/defect

• tools can deposit pain

• they have serial numbers

tool impressions

• can link a tool to a crime scene

• link suspect to crime

• provide other evidence types

recovery of tool marks

• photograph

• use a casting material to make a duplicate of the mark

• recover wrap in cortex or tissue

backward glass fragmentation

• when glass is broken a quantity of it will fly back in the direction it was broken from

• concentric fracture - compression

• radial fracture - tension