Trace Evidence Flashcards
what are the two steps of glass analysis (without composition testing)
- test if it is glass or not
- physically match with a sample on the scene to sample on the suspect
when is glass most commonly encountered at a crime scene
involving motor vehicles, car theft, and burglaries
T/F: glass is not one of the most common and important materials submitted for forensic trace evidence
false
what are most windows and bottles made of?
soda lime, sodium cabonate, calcium oxide, silicon oxide, Na, Ca, Mg, K, Si, O and C
what is the most prominant bond in glass?
Si-O
what are other types of glass on cars and what is the difference to other glass?
heat resistant glass on headlights which will have the Si-O bond but also boron in it.
what is the difference between glass evidence and biological evidence?
glass remains on clothes for a long time and does not degrade/alter over time
how is glass distinguished from plastic?
relative hardness, solubility, and observation with a polarized light microscope
once glass is confirmed what will the examiner do?
test physical properties, optical properties, and chemical composition
T/F: there is a large database of glass refractive indeces.
true
what are the challenges to comparing glass fragments?
- most glass is too small to permit comparison
- individual differences are hard to find
- all glass chemical compositions are relatively uniform
if almost all glass compositions are relatively uniform how can we distinguish them?
trace elements present in the glass
what will certainly exclude glass fragments that originate from different sources?
glass refractive index measurements
who made the glass database?
FBI
what is the most significant refractive index?
1.529 found in 1/2200 samples
if you leave and wash your clothes following a hit and run where can you still find glass fragments
may find some in the laundry room, seating/living room, shoes, and sink
when will you find more glass fragments? and why?
winter because there may be more clothing (more surface area to stick), and more static
what is different between car paints?
almost all manufacters will have a specific proprietor chemical to distinguish
what is the first layer of paint? what is it made of?
this is the E-coat
- epoxy based polymer or resin
- black or gray colour
- slightly different from toyota to honda
what is the second layer of paint? what is it made of?
primer layer
- epoxy based (polyester) or urethane
- white or pigmented
what is the third layer of paint? what is it made of?
base coat
- acrylic polymer
- colour
- binder hold the paint in place
what is the fourth layer of paint? what is it made of?
clear coat
- uncoloured and transparent
- acrylic polymer
- poly urethane polymer
what is the most common amount of paint layers?
four layers
what can be found from analyzing paint samples?
colour, year, make and model of the car
T/F: there is a paint database about the physical paint properties.
false, the database contains chemical properties of paint
how is a microscopic analysis of paint done?
side by side comparison of paint
what are the two possibilites/outcomes for paint analysis?
- two samples are differentiated
- two samples are not differentiated, they are analytically indistinguishable
What should the court know about transferred paint?
the rarity of the paint in the community or the commonality
What is the goal of forensic examination of fibres?
narrowing down the origin to a limited number of sources or even to a single source
What is the challenge of forensic examination of fibres?
mass production of garments and fabrics - limited value of fiber evidence
How does finding specialty fibres help with individualization?
if you find a special fibre associated with a very specific thing it will narrow down who it came from.
what is a natural fibre?
hair, plant-based source, or animal based source
what is a manufactured fibre?
polyester, acrylic, nylon, or spandex
what is most commonly used to examine fibres?
optical microscopy
what are you looking for in fibre examination?
colour, morphological characteristics, diameter, striations, pitting, and particles presence
what is dye composition analysis?
analysing the dye compostion between two fibres
what is level 1 chemical composition testing of fibres?
confirming that all fibres involved belong to the same broad generic class
what is level 2 chemical composition testing of fibres?
confirming that all fibres belong to the same subclassification within their generic class
what is the goal of impression evidence?
to identify a specific source of the impression
what are individual characteristics?
wear and tear characteristic caused by exposure or random manufacturing errors.
what does identification mean in expert language?
definite conclusion of identity
what does probably made mean in expert language?
high degree of association
what does could have made mean in expert language?
significant association of multiple class characteristic (some association but not probable)
what does inconclusive mean in expert language?
limited association
what does probably did not make mean in expert language?
very high degree of nonassociation
what does elimination mean in expert language?
definite exclusion
what does unsuitable mean in expert language?
lacks sufficient detail for meaningful comparison
