trace evidence Flashcards
what does forensic evidence establish
- a crime has been committed
- links between crime scene’s, victim, offender
what is trace evidence?
microscopic quantities of material
probative value in a forensic investigation
what are the different types of trace evidence?
- biological (human)
- physical - biological (non-human)
- particles, substance, marks/ impressions
- natural - manufactured materials
what is forensic value?
it establishes spatial and temporal linke between persons ans scenes of interest
only human faliure to find, study and understand it can diminish its value
what is the process for trace evidence?
transfer –> persistence –> collection–> analysis –> interpretation –> presentation
what are the modes of transfer?
Direct v indirect
secondary transfers
what are the two types of transfer?
one way - useful for looking at gun residue
two way - more useful than one way, gives us more than one way to get evidence of suspect
what is variation in transfer?
it is amount and distrubution of transferred evidence varies.
what are the characterisitcs of varation in transfer?
trace material
properties of source/ recipent
environment conditions
force, duration, type of contact
what is frequency in trace evidence?
transfer is not a discrete event
pre and post crime transfers
what is trace persistance?
temporal dynamics of transferred evidence.
what is trace persistance impacted by?
source/ recipient, environment, evidence characteristics, initial transfer, activity
what is the importance of evidence dynamic?
needs to be taken into account for the limits to prevent misrepresentation/ missues of evidence
what is trace collection include?
scene, lab, person or their possessions
controls samples are important
what is trace analysis?
identified via class characteristics (colour, shape, refractive index) aim to establish point of slimarity between samples
absolute identification often not possible –> exlusion
what are the physcal characteristics for classifying evidence?
melting point
boiling point
refractive index
absorption and emisson spectra
density
molecular mass
colour
species characteristics
what doe non-destructive techniques include
physical and morphological
(microscopy)
what dies the destructive techniques include.
for further information
chemical e.g. chromatography and mass spectrometry
depends on: amount / value of evidence, type of crime, aims of enquire, resources.
