Bloodstain Pattern Analysis (BPA) & Trace Evidence Flashcards
What is BPA?
The study of bloodstains in crime scenes and determining the mechanisms that caused them
What are the bloodstain pattern categories?
Passive bloodstains
* Formed by the force of gravity alone
Projection bloodstains
* Created when blood is propelled by force, energy transferred
Transfer bloodstains
* Occur when a bloody object makes contact with another surface
What are the types of passive bloodstains?
Passive drop
Flow pattern
Drip pattern/drip trail
What are the types of projected bloodstains?
Arterial spurting or gushing
Cast-off
Impact splatter (radiating, back, forward)
Expiated splatter
Gunshot splatter
Area of convergence
What are the types of transfer bloodstains?
Wipe (clean to dirty)
Swipe (dirty onto clean)
What are the BPA methodologies?
- Detailed documentation
- Classification of patterns
- Scene context analysis
- Peer review and validation
What are the three concepts of trace evidence?
Size: small amounts of material
Vestige: physical signs that are left behind
General term: different compositions and variety
What are the most common typs of trace evidence?
- Hairs and fibers
- Arson
- Paint
- GSR
- Glass
What are the two types of labtratory examination methods of trace evidence?
Microscopical examinations
Chemical instrumental analysis
What is a common collection method for fibers?
Tape lifting
What are the macroscopical and microscopical features of hair?
Macroscopical
* Color
* Shape
* Length
* Thickness
Microscopical
* Cuticle (outler layer of hair)
* Cortex (Inner)
* Medulla (Middle stripe)
Note: Humans have a narrower medulla than animals
Humans have a smaller, flatter, less serrated cuticle
Cortex is much wider than medulla in humans
What are the biggest differences between hair from someone of African, European, or Asian ancestry?
African:
* smaller diameter
* flat cross section
* thin cuticle
European:
* medium diameter
* oval cross section
* medium cuticle
Asian:
* largest diameter
* round cross section
* thick cuticle
What about glass is analyzed in forensics?
- Color
- Refractive index (RI)
- Chemical composition
- Physical match
What is a refractive index (RI)?
A measure of how much light bends, or refracts, as it passes from one medium into another
What is the immersion method?
(Glass)
Immersing glass in a liquid of known RI
Becke lines on inside = Glass RI greater than oil
Becke lines on outside = oil RI greater than glass
No bending of light = oil and glass are equal
What are radial versus concentric cracks in glass?
Radial:
Crack happens opposite of force
–> <
Concentric:
If glass is fixed, opposite forces try to bring glass back and cause cracks on same side of force
–> >
These cracks are circular in a spider-web pattern
What are wallner lines?
Ridges on the broken edge of glass (helps determine direction of impact)
Wallner lines and direction:
Radial fractures form right angles on the reverse side
(Draw it out and double check)
Hint: 3 R’s
What are the types of paint classifications?
- Vehicular
- Architectural
- Artistic
What are the layers of metallic and non-metallic paint?
Top to bottom
Metallic:
Clearcoat
Basecoat
Primer surfacer
Primer or electrocoat
Metal substrate
Non-Metallic:
Basecoat (much thicker)
Primer surfacer
Primer or electrocoat
Metal substrate
Lab examinations of trace evidence:
Detection ->
-> Identification
->
1. Sourcing (where?)
2. case linkage (people)
3. Evaluations (Individualization)
