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)
What are the 3 primary classifications in step 6. calssifications of bloodstain patterns?
- Passive stains (caused by gravity)
- Splatter stains (caused by an external force)
- Transfer stains (caused by contact)
How are passive bloodstains primarily created?
Gravity acting on liquid blood
What are the 4 secondary classes of passive bloodstains?
- Drip stains
- Drip pattern
- Flows
- Saturated, pooling
What is a dripstain?
Passive bloodstain
- A bloodstain resulting from a falling drop that formed due to gravity
- Typically result from a bleeding injury or blood falling from an object
What is a drip trail?
Passive bloodstain
- A bloodstain pattern resulting from the movement of a source of drip stains between two points
- Directionality may sometimes be established from the stain shape and edge characteristics
What is a drip pattern?
Passive bloodstain
A bloodstain pattern resulting from a liquid that dripped into another liquid, at least one of which was blood
What is flow pattern?
Passive bloodstain
A bloodstain pattern resulting from the movement of a volume of blood on a surface due to gravity or movement of the target
What is a saturation stain?
Passive bloodstain
A bloodstain resulting from the accumulation of liquid blood in an absorbent material
What is the definition for splatter stains?
- Bloodstain resulting from a blood drop dispersed through the air due to an external force applied to a source of liquid blood
- Splatter stains are typically small and elliptical/circular in shape
How is a splatter stain formed?
- Splatter stains are formed from droplets of blood in flight
- Created in respinse to a force applied to the blood
- Resulting pattern is dominated by small circular and elliptical stains
What are 5 common mechanisms for splatter?
- Impact
- Expiration
- Arterial pressure
- Cast-off (motion object)
- Firearms
What is an impact bloodstain?
Splattered bloodstain
A bloodstain pattern resulting from an object striking liquid blood
What is a cast off bloodstain?
Splattered bloodstain
A bloodstain pattern resulting from blood drops released from an object due to its change in motion
What is an expirated bloodstain?
Splattered bloodstain
A bloodstain pattern resulting from blood forced by airflow out of the nose, mouth or a wound
What is projected bloodstain?
Splattered bloodstain
A bloodstain pattern resulting from the ejection of a vloume of blood under pressure e.g. arterial breach
What is the definition of transfer stains?
A bloodstain resulting from contact between a blood-bearing surface and another surface
What are 3 types of transfer stains?
- Pattern transfer
- Wipes
- Swipes
What is a wipe bloodstain?
Transfer bloodstain
An altered bloodstain pattern resulting from an object moving through a pre-existing wet bloodstain
What is a swipe bloodstain?
Transfer bloodstain
Bloodstain pattern resulting from the transfer of blood from a blood-bearing surface onto another surface, with characteristics that indicate relatvie motion between the two surfaces
What is a pattern transfer bloodstain?
A recognisable mirror image or at least a recognisable portion of the original surface may be transferred to the second surface
What is a void (shadow) bloodstain?
The absence of bloodstaining in an otheriwse continuous bloodstain or bloodstain pattern
How many levels of bloodstain pattern analysis are there?
4 levels
What is level 1 of BPA?
The searching for stains that can be identified as blood
What is level 2 of BPA?
The evaluation of the physical appearance of a bloodstain and its primary classification
What is level 3 of BPA?
The combination of the physical appearance and knowledge of the behaviour of blood allows a consideration of possible transfer mechanism and a secondary classification of the bloodstain
What is level 4 of BPA?
An evolution of the case facts, witnesses testimony, crown and defence assertions leads to the development and testong of reconstruction theories
