Deep Dive into Trace Evidence Flashcards
What did Edmond Locard say?
Locards exchange principle:
it is impossible for a criminal to act, especially considering the intensity of a crime, without leaving traces of this presence’
He never actually said ‘every contact leaves a trace’
What type of data is trace evidence?
- it is proxy data
- it provides a link between people locations and objects
What does trace evidence aid?
it aids crime reconstruction:
- transfer - where does the trace come from
- persistence - when was the trace transferred
- activity level - how did it get there?
What is recommended for the amount of evidence that is needed for a case?
- never rely on just one piece of evidence e.g. DNA
- use lots of trace evidence (it is like a rope and if one strand of rope breaks then the whole chain is fine)
When looking at trace evidence what must we consider?
background levels, 10, 20, 30, and 40 transfer
What happens in a case where neither DNA nor fingerprints database reveal any matches?
use trace evidence
What are the three levels of evidence?
inceptive - has a crime been committed or not?
identification - fingerprints/marks and DNA
associative - has contact occurred?
What are the five trace evidence considerations?
1 - strength of TE is determined by case context and material ‘uniqueness’
2 - two-way transfer but one of transfers is more obvious than other e.g. additions to scene easier to spot than removals
3 - TE is least understood and most overlooked
4 - non-contact transfer, in addition to primary, secondary and tertiary
5 - absence of evidence doesn’t equal evidence of absence
What six factors do you think would affect trace evidence transfer? what might increase the amount of trace transferred?
1 - nature of material
2 - shedding (wool more likely to shed than silk
3 - substrate
4 - nature of contact (pressure)
5 - frequency (similar to amount of time - how many times contact occurred and how long for)
6 - surface area
What nine factors do you think would affect trace evidence persistence? What might hasten evidence degradation?
- as with transfer considerations (nature of material, substrate and nature of contact) but also
1 - emergency services intervention
2 - contamination
3 - post-deposition activity (shower after committing crime)
4 - cleaning/laundering (clean surfaces and wash clothes)
5 - environment/weathering (temp of environment)
6 - animals/microorganisms (unintentional scavengers, bacteria and viruses)
7 - crime to recovery time
8 - recovery to analysis time
9 - trace embedding (fluffy carpet vs wooden floor, embedded in wool vs stuck on wall)
What are the nine trace evidence challenges?
1 - efforts of emergency personnel
2 - scene tampering - CAPs and cordons
3 - not detected (don’t always find everything)
4 - detected but value not recognised - do not see importance
5 - detected and recognised but not relevant to case
6 - overwhelming amount of trace - anything can be evidence
7 - inappropriate collection techniques (loss and damage)
8 - inappropriate storage (loss and degradation)
9 - inaccurate interpretation
What are the ten considerations when recovering evidece?
1 - recover trace or the entire item?
2 - gloved hand or tweezers?
3 - wet samples?
4 - gelatine lifters (created to lift prints without developing them but will pick up all trace evidence, they are made of collagen and it is a protein so DNA will interfere with collagen e.g. makeup samples)
5 - sequential vs zonal tape lifting
6 - vacuum sweeping
7 - swabbing - not always best for TE
8 - control samples
9 - ESLA (not just for footwear marks, it picks up TE too - the dust that makes up the footwear mark)
10 - hinge lifters (not just for fingermarks - can find drugs of abuse, makeup, glass, paint fragments)
What is the Sydney Declaration?
It provides a definition of forensic science and seven fundamental principles
What are important take home messages from the Sydney Declaration?
- trace is not something very small or something at the analytical instruments detection limit - can be as large as megalith or as small as GSR particle
- traces can be digital now too (a lot of peoples lives are on the internet)
- traces are diverse and their detection, recognition, recovery, examination and most if interpretation still relies on human intervention however we make mistakes
- CSI and reconstruction are hardest part of FS and shouldn’t be treated same as technical exercise in gathering obvious traces
- opinion and interpretation are most important aspects of trace evidence analysis e.g. building materials in builders van = normal but in a car = not normal
- we won’t ever really know truth unless person that did it tells us - reconstruction is based on logic, scientific research, traces in front of u and prerequisite knowledge
- specific retrodictive model - trying to guess something that happened in past (not predictive model where trying to predict something that will happen in future
- context is paramount; background, transfer, persistence and activity. would you expect the number, type and distribution of fibres to be the same if you gave them a gentle hug or hit them?
Why might inclusion of TE in a criminal investigation be beneficial? (7)
- TE doesn’t lie, have an agenda, forget things, succumb to emotion or misinterpret scenarios (it is a mute witness/proxy data.)
- traces can provide evidence of association or contact, between people, places and/or objects. (Locards principle)
- traces can assist in crime reconstruction, i.e. activity level propositions (the difference between a hug and a fight).
- TE provides robust and complementary evidence in casework, akin to pieces of a jigsaw puzzle (rope analogy)
- can no longer rely exclusively on DNA evidence as the sensitivity of its analysis means contamination is a problem
- TE can provide valuable evidence where DNA and fingermarks presence would be legitimate, e.g. where a crime is committed between inhabitants of the property.
- where no matches are revealed on either the DNA or fingerprint databases, traces can provide investigative leads
