Flashcards in Trace Evidence Analysis Deck (32)
What evidence can be viewed under a microscope?
Light sources for objects and garments
What is the procedure of collecting trace evidence?
Characterisation and comparison
Assessment of significance
Safety of trace evidence (preservation/reliability)
What is trace evidence?
Very small amounts of material
Provides a link between suspect and victim/locus
What is Locard's principle?
Every contact leaves a trace
What are some examples of trace evidence?
Fibres (natural vs. artificial)
What is a reactive trace?
Know something about the suspect, looking for links, i.e. suspect wearing red cardigan described by witness, look for that on victim
What is an inceptive trace?
Don’t know anything about suspect, find red fibres on victim, make connection. Find trace evidence don’t know who it’s come from actively link to suspect
What are different variables in types of material?
Amount of material- amount of material available for transfer
Nature and duration of contact, length of time of contact
Persistence of material- size, surface of receiving material, grooves on shoes
Finding the material- shaking, brushing
Evidence value of the material
What are the main ways to recover evidence obtained?
Shaking- shake garment to get material
Brushing- pocket lining brushing to remove trace material
Taping- recovers hair and fibres
Vacuuming- minute particles e.g., firearm discharge residue
Swabbing- small amounts of smeared material, e.g. blood, fluids
Hand picking- glass, leaves
What is the key information obtained from glass?
Shape, colour, thickness
What is the physical analysis of glass?
Refractive index (most common 1.5)
What is the chemical analysis of glass?
Scanning electron microscope (chemical characteristics, different radiation patterns)
What is a fibre?
Any long thin flexible solid objects with a high length to transverse cross-section are ratio
What are examples of natural fibres?
Animal, vegetable, mineral
What are examples of man-made fibres?
How do you analyse fibres?
Low power microscopy
Cross-sectional shapes- thickness
TLC (Thin Layer Chromatography)- removes dyes present in fibres
Infra Red Spectroscopy (particularly man-made fibres)
What is the hair made up of?
Medulla, Cortex, Cuticle
What is the Medulla?
Middle, collapse cells, sometimes difficult to see
What is the Cuticle?
Outside, scale cells
Where a possible sources of hair?
Clothing, bedding, sheets, weapon, car seats
Is the scaling the same or different in other mammals hair?
What is the classification of hair?
Human, animal, body part it’s come from, determine race, any artificial alteration (e.g. wig, hair dye)
How do you examine dyed hair?
What are the phases of hair?
What is the Annogen phase?
Actively growing hair
What is the Telogen phase?
Hairs finished growing
What is the DNA issue with hair?
Can only obtain DNA evidence if root is obtained, only mitochondrial DNA can be collected if its from the body
What other information can hair give you?
How is evidence assessed for significance in terms of comparison?
How much analysis has been carried out, how much characterisation and comparison
What is the usefulness of rare evidence?
The less common the easier to produce a conviction
What are the issues with trace evidence?
Innocent sources accused due to secondary or even tertiary transfer
If contamination evidence is not reliable in court