Bloodstain Pattern Analysis Flashcards
bloodstain pattern analysis
an in-depth evaluation of bloodstain pattern
factors to consider in bloodstain pattern analysis
- size
- shape
- number
- dispersion
- volume
- location
what does BPA define?
the nature of the action that created it
determinations from blood stains
- height of impact
- direction of travel
- angle of impact
- nature of the force
- relative positions of individuals at a scene
- the sequence of events may have occurred
Dr. Eduard Piotrowski
- first known, systematic study of bloodstain pattern
- concerning the origin, shape, direction, & distribution of the bloodstains
Victor Balthazard
- explained Forensic Medicine importance to Congress
- recognized empirical relationship of stain shape to angle impact
- introduced the ‘stringing concept”
Herb MacDonell
- published seminal studies & provided the first training
- flight characteristics & stain patterns of human blood
SWGSTAIN
mission to promote and enhance the development of forensic bloodstain pattern analysis practices through collaboration of government forensic laboratories, law enforcement, private industry, and academia
what is blood affected by?
- gravity
- surface tension
- viscosity
- air resistance
what holds a blood droplet together in flight?
surface tension
gravity is consistent =
blood in flight in consistent
viscosity
the resistance to flow
what is the effect of air resistance dependent on
droplet size
the smaller the droplet …
the greater the force effect
does blood spontaneously breakup?
not unless it is acted upon by an external force
what path does blood take?
the path of least resistance
what special property does blood have?
an adhesive property
Pattern Diversity Principle
combination of blood volume and forces acting on those volumes results in recognizable classes of patterns
Principle of Stain Shape & Vector
the shape of the bloodstain provides indicators as to the direction of deposition & spatial origin of the blood
Physically Altered BPA Principle
exposed blood will react to environmental conditions in a predictable manner
what force produces a high velocity blood splatter?
an external force greater than 100 feet/sec
high velocity blood splatter stains
- sometimes referred to as a mist
- tend to be less than 1 mm
what creates high velocity blood splatter?
- usually created by gunshots or explosives
- may result from industrial machinery or expired air (coughing or sneezing)
high velocity blood splatter travels
travels the shortest distance because of the resistance of the air against their small mass
what force produces a medium velocity blood splatter
an external force between 5 feet/sec and 25 feet/sec
medium velocity blood splatter stains
generally measure 1 to 3 mm
what creates medium velocity blood splatter?
- blood flying from a body to a surface as a result of blunt or sharp force trauma
- body colliding with rounded or edged surfaces/vehicles
what creates a low velocity blood splatter?
an external force less than 5 feet/sec (normal gravity)
low velocity blood splatter stains
generally 3 mm and larger
what causes a low velocity blood splatter?
- blood dripping from a person walking or running
- bloody weapon
low velocity blood splatter drips
dripping blood often falls at a 90° angle & forms a 360° (circular) stain when it hits a flat surface
3 types of bloodstains
- passive
- splatter
- altered
example of passive bloodstains
gravity
example of spatter bloodstains
energy applied creating flight
example of altered bloodstains
physically/environmentally altered
passive blood stains
- drop(s)
- flow
- large volume
spatter bloodstains
- impact mechanism
- secondary mechanism
- projection mechanism
secondary mechanism
spines & satellite stains
satellite stains
smaller bloodstain originating from a larger blood stain
altered bloodstains
- time lapse
- diluted
- diffused
- insects
- contact
- voids
wipe
moving through a pre-exisiting blood stain
swipe
transfer from a blood bearing surface
the basic premise of BPA theory
based on stain size, shape, volume, orientation, & other physical characteristics, the analyst can differentiate between basic types of blood shed events
what must an analyst do to support any claim about a pattern?
must be able to articulate what characteristic led him to his decision
BPA scientific process/method
- data collection/gather case information
- segregate patterns, then categorize the patterns
- documentation, notes of sizes, shapes, directionality, areas or origin, etc
- evaluate different hypotheses
- test different theories
- conclusions/results, supported by physical evidence
- peer reviewed
area of convergence
the area containing the intersections generated by lines drawn though the long axes of individual stains (2D)
a longer blood stain is formed by
a lower angle of impact
what increases spatter diameter?
height
when do spines appear at the edge of a stain?
when blood drops come from greater heights
direction of tail =
direction of blood
equation: angle of impact
sin theta = width / length
determining the area of origin
- 3D location from which spatter originated
- using the stringing method
presumptive test
- indicates possible presence of a substance
- “this is likely saliva”
confirmatory test
- conclusively identify a substance
- “this is definitely human saliva”
pros of presumptive test
- narrow possibilities & helps to decide which test to do next
- can use on large areas
- can locate evidence not visible with the naked eye
- cost effective
- portable
- sensitive
cons of presumptive test
many false positives
pros of confirmatory test
- conclusively identify a substance
- wont waste money when moving on to DNA testing
- MUCH smaller risk of false positives
cons of confirmatory test
- higher cost
- require additional equipment
- takes longer
screening for bodily fluids - when not readily apparent
- many body fluids fluoresce under a black light
- things that fluoresce contain phosphors
body fluids that fluoresce
- urine
- saliva
- sweat
- semen
phosphors
substance that absorbs energy outside of the visible spectrum & re-emits the energy as visible light
blood under a black light
- does not fluoresce
- it sometimes appears darker
Human Blood Presumptive tests
- Kastle Meyer Test
- Luminol
- Alternate Light Source
Human Blood Confirmatory tests
- Precipitin test
- Hematrace
- does not confirm DNA presence
quality control
are the tests running properly?
quality assurance
does the whole program work?
negative control
not expected to produce results
positive control
expected to produce results
what should be a positive control?
where blood is present
what should be a negative control?
where blood isn’t present
Presumptive Blood Tests (Luminol & Phenolphthalien)
- uses hemoglobin to catalyze the oxidation of certain reagents
- hydrogen peroxide often used as oxidizing agent
- visible as a color change
Confirmatory Human Blood Test
- Precipitin Test
- ABAcard Hematrace
ABAcard Hematrace
- remove a piece of fabric/swab with suspected blood
- add to provided vial (containing buffer) & shake
- remove liquid from vial & put two drops in the same wells
Human Semen Presumptive Tests
- Acid Phosphatase
- Prostate Specific Antigen
Human Semen Confirmatory Tests
- look under a microscope for morphology and stains
- look for christmas tree in sperm
Acid Phosphatase Test
- presumptive test
- semen will produce a positive color change in < 1 minute
- affected by concentration & age of stain
presumptive & confirmatory tests - Saliva
based on the presence of saliva alpha amylase
Saliva Presumptive Test
Phadabas
Saliva Confirmatory Test
RSID (Rapid Stain Identification) Test
neutralization test
if AB antigens are present in the fluid they will react with (neutralize) antibodies, so that they don’t interact & agglutinate red blood cells with the same antigen
saliva + antibody A + A Type RBC = no agglutination
saliva from a secretor of A saliva
saliva + antibody A + A Type T RBC = agglutination
saliva from a non-secretor or saliva from a secretor without A type RBC
