L18 - Introduction to Bloodstain Pattern Analysis Flashcards
What is the definition of bloodstain pattern analysis (BPA)?
Bloodstain pattern analysis is the sudy of the shapes, sizes and locations of bloodstains in association with knowledge of the underpinning sciences (physics, mathematics, and biology) to provide information on the event or a sequence of events that resulted in the deposition of these bloodstains or bloodstain pattern
Where can bloodstain patterns be interpreted?
- At a scene (indoor, outdoor, vehicle, on a body)
- In the laboratory (clothing, footwear, weapons)
- From photographs
What can bloodstain pattern evidence determine?
- Area of origin(s) of blood
- Distance between target surface and origin of blood
- Type and direction of impcat that produced bloodstains
- How many blows/shots (or a minimum number)
- Position of bleeder
- Sequencing, when different stains are deposited
- Obtain pertinent stains for further analysis (DNA)
What are some examples where BPA can be of great use?
- Determining the cause of an unexplained death (homicide/suicide/accidental)
- Body is at ‘odds’ with scene
- Assessing claims by witnesses and accused
- Defence of suspect is ‘self defence’ or ‘helpful bystander’
- Two or more persons have bled at a scene
- Mulitple blood patterns observed
What is a bloodstain?
Any blood deposit on a surface, can be any shape or size and often occur in groups (bloodstain pattern)
What is the scientific process for BPA
- Scene/item overview
- Locating blood
- Documentation/record observation
- Analysis of elliptical stains
- Placing stains into groups
- Classification and interpretation
- Formulate hypothesis and theories
- Form conclusion
What occurs during step 1. scene/item overview?
- Define boundaries of examination
- Document conditions
- Limit contexual infromation to minimise biasing effects
What occurs during step 2. locating blood?
- Search and identify visual stains
- Use presumtive chemical tests for confirmation
- Low power stero microscope
- Search for non visible blood with enhancements (NIR near infared camera, chemical enhancements e.g. luminol)
What is luminol?
A chemical reagent which reacts with traces of blood to produce a chemiluminescent reaction
What is one downside to luminol?
The reaction must be viewed in the dark making documentation difficult
Is luminol sensitive or specific?
- Luminol is very sensitve but the least specific chemical test for blood
- False positives can occur
Who can interpret the results?
Poeple with training and experience are required to interpret the results
What will luminol reveal?
What blood patterns
- Trace (non-visible) levels are antcipated
- Clean up of blood is suspected
- Movement of body/objects e.g. dragging of a body
- Patterns may be present e.g. footwear, footmarks
What is recorded during step 3. recording observations?
- The number of bloodstains
- Location
- Size
- Shape (including directionality)
- Colour and intensity of blood within stain
- Spatial relationship between bloodstains
- Spatial relationship between bloodstains and other objects or surfaces nearby
- Alteration/disturbance of different stains
- The surface characteristics of the material (target) upon which stains are deposited
What occurs during step 4. analysis of elliptical stains?
- Look at drip stains and angle of drip stain
- As the angle decreases the length increases, stains become more elliptical (W:L ratio decreases)
- Area of origin determined by combining the directionality of selected stains with their angle of impact, the straight line trajectory can be estimated
What are common charcteristics observed during step 5. placing stains in groups?
- Same location
- Similar size/size range
- Shape of stains (including directionality)
- Originate from common area (share 2D or 3D convergence)
- Overall shape/distribution of stains (radial, linear, curvilinear)
