11. Trace Evidence Analysis Flashcards
What is trace evidence ?
Name some examples
Very small quantities of materials
Locards principle - every contact leaves a trace
Key examples - hairs fibres and glass fregments
Whats inceptive search ?
Extract distinctive material
Whats reactive search ?
Looking out for particular material based on other information
Name some recovery methods
Shaking Swabbing Vacuuming Tape-lifting Brushing
What is naturally shed hair called ?
Telegen
What is torn out hair called ?
Anagen
What is hair comprised on ?
Keratin
What are the racial origins of hair ?
Caucasoid
Mongoloid
Negroid
Whats the structure of hair ?
Outside - cuticle
Inside - cortex
Medulla
Cortical fusi
Pigment granule
Whats a fibre ?
Smallest unit of a textile which has been spun into thread
Why can fibre evidence be individualised ?
Because of the variety of physical and chemical characteristics
What are natural fibres ?
Animal fibres ( silk, wool, hair ) vegtable fibres ( linen, cotton, jute, kapok, coir ) mineral fibres ( asbestos )
What are organic fibres ?
Synthetic polymers - polyethene,polyamide,polyester
Natural polymers -
Cellulose, materials, rubber
What are inorganic fibres ?
Carbon, ceramic, glass, metal
How to compare fibres ?
Establish points of identity
Avoud contamination
What can a compound microscrope see from fibres ?
Diamater Shape Surface features Colour Refractive index Burefringence - determinning chemical nature
Stereo microscope
Low magnification
Hairs - classify individualise
Natural fibres - identify classify, finres appearance and distribution
Sumthetic fibres - indentify classfiy fibres appearance and distribution
Compoun/polarised microscopy
High magnification
Hair - classify measure identify features
Natural fibres - classify measure indentify features fluorescence
Synthetic fibres - classify and measure fuvres by optical properties, refractive index , birefringence
Comparison microcscapy
Manification ranges
Hair - comapre questioned and knows fibres
UV visible microspectrophotometry
Characterises colour of the fibre
Infared microspectroscopy
Identify molecular composition of the Phiber
Thin layer chromatography
Separate the dyes extracted from the fibre
What colour is 650nm ?
Red
What nm is violet ?
400
Technique of uv spectroscopy
Hair - identify coloursnts and dues on the hair
Natural fibres - identify dyes on fibres
Synthetic fibres - identify dyes on fibres
Technique of IR spectroscopy
Hair - na
Natural fibres - na
Synthetic fibres - identify , classify the chemical nature of the fibre
Technique of thin layer chromotography
Hair, natural fibres, synthetic fibres - identify dyes and chemical treatments
Technique of neutron activation analysis
Hair - identify and quantify trace elements in hair
Natural fibres - na
Synthetic fibres - na
What is glass ?
A amorphous solid based on sand , manifactured at 1600c using silican or limestone or alumina
How is glass classified and individualised?
Flatness Optical prowprties Density Refractive index Analyse of trave elements
Float glass will fluoresce under how much uv ?
254nm
How to determine glass density ?
Suspending fragments in liqudi of known density
What 2 ways to analyse for trace metals in glass ?
Optical emission
Or x-ray fluorescence soectroscopy
What year was the glass case in new zealand ?
1991
Pharmacy was robbed , the suspects clothes were analysed to find what?
11 glass fragments and small flakes of yellow paint were found on suspect A
3 fragments and more yellow paint chils found on B
Glass was examined and this showed ?
Flat glass urgaves and uv fluorescence showed fragmenrs were plate glass
What was concluded ?
Glass evidence supported paint chips
What are paint chils formulaed oht of ?
Binder, pigment and solvent
Whats the key component of paint chips?
Pigemnt
How are paint chips examined ?
Microscopy , colour looked at via Microspectrophotometry
Chemical charcetristics - ir spectroscopy
Organic compoents - purolysis gad chromotography
