Analytical Techniques For Trace Evidence
No description yet. This curated deck is ready for daily study.
Card preview (24)
What kind of cases might require chemical analysis of glass evidence ?
-burglary -car accidents -assault
Why is the location of glass relevant ?
The location of glass is dependent on what is analysed/ evidential value
How is glass recovered from clothing/ shoes ?
-seal pockets/ trousers turn ups -recover hairs/ fibres by lightly taping -shake item/brush onto brown paper -check pockets and turnups last
How is glass and fibres recovered from hair ?
Combing
How is glass and fibres taken from other surfaces ?
Tweezers
What controls are taken from glass recovery ?
-blank sample -reference sample at crime scene is taken from the frame not from the glass on the floor
When would a forensic scientist analysis glass ?
-SOCOs will recover glass or size items with glass on it. -volume crimes- don’t usually examine glass because a suspect is not located quickly enough -serious crimes-more likely to analyse glass evidence
What is the evidential value of glass in hair combing ?
Highest evidential value
What is the evidential value of glass embedded in soles of footwear ?
Lowest evidential value
What is float glass ?
-very common (windows) -smashes into mixed sized fragments with sharp edges -edges can tell us how fresh the smash was
What is tampered glass ?
-common (motor vehicles) -safety glass -hard to smash -forms cubes -tends to clump together -edges indicate thermal or physical stress and impact
What is laminated glass ?
-2+ panes joined by plastic (PVB bond) -common (windscreen glass) -less common (bullet resistant, smart glass) -sticks together -safety
What is wired glass ?
-less common (fire doors) -mesh through the pane -tends to be indoors (rusting)
How does glass smash ?
Backwards fragmentation
What is a radial crack ?
Radiate in Amy directions away from the point of fracture
What is a concentric crack ?
Imperfect circle around the point of fracture
What are the different types of analysis for glass ?
-chemical -refractive index -mechanical fit
What is chemical analysis for glass ?
Identifies oxides in colouring and impurities in constituent parts used in manufacture
What is refractive index analysis for glass ?
Light refraction as it passes through glass, measured in heated oil. The RI changes as it’s heated, and when the sample disappears the RI value is known
What is mechanical fit for glass ?
Large fragments might stick together Conchoidal stress marks
What equipment is used to analyse glass ?
-GRIM -X-Ray fluorescence -Scanning electron microscope -surface examination -annealing
What is GRIM analysis ?
Measures optical properties of glass -tiny fragments <0.5 mm
What is X-Ray fluorescence analysis ?
Elemental composition of glass
What kind of cases might require chemical analysis of fibre evidence ?
-hit and run -car crash/ accident -sexual assault -burglary