Persistence of Trace Evidence Flashcards
What dose the amount of persistence depend on?
The size and shape of the particle
The amount deposit
The texture of the recipient material
The mode of contact
Activity between deposition and recovery
The nature of the environment
The amount of time passed
What is the forensic linkage triangle?
Consists of the Suspect, Victim, and Scene
Physical evidence serves to connect or show a link between any two of these components.
What is the importance of partical size?
Small particles will presist for longer than larger particles, as they
are more likely to become logged in the surface material.
e.g. Clay particles to persistent on footware for longer than sand particles.
Gun shot residue has relativlet large particles and has lower persistence
What are the difference in Surface textures?
Particles with irregular surfaces (Glass fragments), or rough surfaces (Wool fibres) tend to remain longer than smooth surfaces (Nylon).
The amount of material available for transfer and how readily traces are shed from the original material.
Mode of contact e.g. material that produces smearing on contract will last longer than parrticulayes being temporarily logged because a smear includes a physical bond with the receiving surface.
What case study can be realeted to this?
Stephen Lawernece
All of the evidence had been missed by forensic examinations in 1993 and 1995.
LGC carried out stereo microscopy examination which was deemed too time-consuming in 1993 and 1995
Experts pointed out that scientists them were not looking for microscopic blood stains as even if any had been discovered they would have useless as DNA testing had not yet been developed enough to be able to clarify that such a small stain was blood belonging to Stephen Lawerence
If material is outside you need to?
Prioritise
Improvise
Adapt
Overcome
Document
Defend
If material is outside what additional assets are needed?
Experience
Quickthinking
Advanced planning
If there is evidence outside what advanced planning is critical to have?
Pop-up tents
Waterproofing
Coverings
Cool boxes
Drying cabinets
What critical considerations are needed for outside evidence?
Protect personnel
Protect equipment
Protect evidence
What were the 5 contextual effects identified by Rynearson and Chisum (1989)?
- Predictable effects
- Unpredictable effects
- Transitory effects
- Relational details
- Functional details
What are the 4 questions that investigators should ask about evidence?
- What is it?
- What function did it serve?
- What does it tell us about timing and sequencing aspects?
- What interrelationships does it hold to other evidence?
What are some Aide Memoirs?
- Air / Room temperature (essential in COT deaths)
- Premises lighting On/Off
- Fires On/Off
- Weather forecast (outside scene)
- Tape lift body (prior to removal)
- Tape lift clothing if necessary
- Bag head Hands and feet
- Consider BPA (Body and scene)
- Seized relevant CCTV tapes
- Technical equipment (Metal detectors etc)
- Street lighting times
- Stepping plates
- Ambulance - paramedics (contamination issues)
What are some predictable effects?
Rhythm or regularity
Links to time since death estimated
Chemical changes changes the way a fire spreads, decomposition of textiles, forensic entomology, rigor/livor/algor mortis, Also seasonable/environmental.
What are some unpredictable effects?
- May cause significant alteration and misinterpretation of original scene
- E.g entry of first people into scenes, disturbance of an item, creating a path to assist body recovery.
- Often the ambulance staff and first attending officers will have already approached the body in an attempt to preserve life.
- Staff are aware of scene prevention but often they have to follow the most direct route. It is important to obtain a record of their actions at the scene and any elimination footware etc.
What are some Transitory effects?
Burning cigarettes
Melting ice
Odours
Heat dissipating
Temperature
What are some rational details?
Correlation between objects, e.g cluster of shells casings, distance between weapon and deceased, void in blood spatter, depth of burial, items to assist the interpretation of death involving unclear sexual contest.
Crime scene sketch and measurement critical in documenting relationships.
What are some functional details?
Clocks
Watches
Guns
Locks
Mobile devices
Tvs
Ring door bells
In order for scientists to be slective about trace evidence they need to consider what?
- How much material is likely to have been transferred in the first place.
- How well this might have persisted
- The ease with which the searcher is likely to find it
- The evudential value of any trace material found
- Context effects
