Bloodstain Pattern Analysis (BPA)

Bloodstain pattern analysis

-an in-depth evaluation of bloodstain pattern

-many factors considered: size, shape, #, dispersion, volume, location

-to try to define events that occurred during the blood letting incident

Determinations from bloodstains

-height of impact

-direction of travel

-angle of impact

-nature (speed) of the force

-relative positions of individuals at a scene

-the sequence of events that may have occurred

BPA history

-Dr. Eduard Piotrowski (1895) first known systematic study of bloodstain pattern: “concerning the origin, shape, direction and distribution of the bloodstains following head wounds caused by blows”

-Victor Balthazard (1939) explained importance to congress of forensic medicine: recognized empirical relationship of stain shape to impact angle, “stringing concept”

-Herb macdonell (1970) published seminal studies and provided the first training: flight characteristics and stain patterns of human blood

SWGSTAIN

-to promote and enhance the development of quality forensic bloodstain pattern analysis (BPA) practices through the collaborative efforts of government forensic laboratories, law enforcement, private industry, and academia

Blood droplet dynamics

-blood is affected by gravity, surface tension, viscosity and air resistance

-gravity is constant = blood in flight is consistent

-surface tension holds a blood droplet together in flight

-viscosity is the resistance to flow (hit/add pressure to blood makes it more viscous)

-effect of air resistance is dependent on droplet size (smaller droplet = greater the force effect)

blood droplet dynamics

-blood will not spontaneously break-up unless acted upon by an external force

-blood takes the path of least resistance

-blood has an adhesive property

BPA principles

-pattern diversity principle

-principle of stain shape and vector

-physically altered BPA principle

pattern diversity principle

-combination of blood volume and forces acting on those volumes results in recognizable classes of patterns

principle of stain shape and vector

-the shape of the bloodstain provides indicators as to the direction of deposition and spatial origin of the blood

physically altered bpa principle

-exposed blood will react to environmental conditions in a predictable manner

old system: LVIS, MVIS, HVIS

-low, medium, and high velocity impact spatter

high velocity blood spatter

-produced by an external force greater than 100 feet/sec

-stains, sometimes referred to as mist, tend to be less than 1mm

-usually created by gunshots or explosive, may result from industrial machinery, or coughing or sneezing

-travel the shortest distance because of the resistance of the air against their small mass

medium velocity spatter

-an external force >5 feet/sec but <25 feet/sec (greater than gravity)

-generally, measure 1-3mm

-most created by blood flying from a body to a surface as a result of blunt or sharp trauma or the body colliding with rounded or edged surfaces/vehicles

low velocity spatter

-external force less than 5 feet/sec (normal gravity)

-generally, 3mm and larger

-result from blood dripping from a person walking or running, or from a bloody weapon

-dripping blood often falls at a 90-degree angle and forms a 360-degree stain when it hits a flat surface

Bloodstain pattern categories: bloodstains

-passive (gravity)

-spatter (energy applied)

-altered (physically/environmentally altered)

Bloodstain pattern categories: passive

-drop(s)

-flow

-large volume

bloodstain pattern categories: spatter

-impact mechanism

-secondary mechanism

projection mechanism

secondary mechanism

-spines and satellite stains

satellite stain

-smaller bloodstain originating from a larger blood stain

Bloodstain pattern categories: altered

-time lapse

-diluted

-diffused

-insects

-contact

-voids

wipe versus swipe

-wipe: moving through a pre-existing bloodstain

-swipe: transfer from a blood-bearing surface

classification (taxonomy) versus conclusion

-based on stain size, shape, volume, orientation and other physical characteristics, the analyst can differentiate between basic types of blood shed events

-must articulate on what characteristics led them to believe this decision

BPA scientific process/method

-data collection/gather case info

-segregate patterns, then categorize patterns (taxonomy)

-documentation (notes and photos, size, shape, direction, area of origin, etc.)

-evaluate different hypotheses

-test different theories

-conclusion/results, supported by physical evidence

-peer-reviewed

area of convergence

-the area containing the intersections generated by lines drawn through the long axes of individual stains (two-dimensions)

direction

-“tail” of blood stain points in direction of travel

blood drop elongates

-the longer the blood stain the lower the angle of impact

-spatter diameter increases with height + spines appear at edge of stain from greater heights

angle of impact

sin-1 (width/length)

determining the area of origin

-3-D location from which spatter originated

-uses the “stringing” method

-closer drops makes it easier to overestimate

-can always come down from a point