Blood spatters and stains
Bloodstain pattern analysis
What is blood?
vital complex biological fluid
contains red blood cells
only in vertebrates
has different color, texture, physical properties, and behavior
What is a bloodstain pattern?
a bloodstain pattern is a physical geometric image created by blood contacting a surface or vice versa
we want those created once blood leaves the body
bloodstain pattern analysis (BPA)
interpretation of information presented by pattern
info based on inferences relating to actions that took place during an event
helps with reconstruction of crime scene, corroborating statements and identify actors
physical evidence
Methodology for analysis of bloodstain patterns
physical properties: surface tension, viscosity, internal cohesion, drop formation, fluid dynamics, specific gravity, aerodynamic behavior
physical actions of blood prior to, during, and after contact with a surface.
Image recognition, physical and mathematical interpretation of patterns, corroborative research and logical inferences.
probable info from bloodstains
direction
angle of impact
origin
applicable forces
trajectory
object id
actors positions
sequence of events
left/right handedness
clothed/unclothed
non-linear behavior
physical properties affecting bloodstain patterns
origination surface construction
impact surface construction
temperature
humidity
time
actor movement
contamination
distance
impact surface consideration
course surfaces cause irregularities in patterns
blood may break up on impact, follow contour of surface
impact angles and directionality become less reliable as a surface becomes more porous
bloodstain pattern recognition-pattern types
passive
flow, pool, saturation, drip/drop, volume
laying down, perfect circle, actor not moving
projected pattern
- instrumental, expirated, arterial spurt/gush
tracheotomy wound, missing appendage
impact pattern
- blood splashes, object splashes, drops, drips, trails, object impact
slow motion punch
impression pattern
- transfer contact, swipe, wipe, secondary
hair acts as brush
artifactual pattern
- voids, fly spots, insect/bug trails, bubbles, dried skeletonized, spearated blood
backsplatter - ejection of blood and tissue from entrance wound of a gunshot
angle of impact
- determined by dividing the width of a bloodstain pattern by the length and multiplying it by the arcsine to get the degree of the angle
angle = arcsin(w/l)
blood that impacts the surface at a 90 degree angle will be nearly round
as the angle decreases the tail of bloodstain wil increase. tail will point in the direction that the blood was traveling
origin of bloodstain
the place from which the blood came from in space, its physical location
3D points of origin can be determined by several methods
stringing, computer models, mathematical/right angles
math: A² + B² = C²
B = tanA
blood for purposes of reconstruction
identify and locate actors
bloodstaidn patterns locate actions
actors= actions suggest scenario
scenario may suggest motive
blood as evidence
photograph
measure
use clean instruments
dry/refrigerate
document patterns
purple tops = dna
rep tops = toxicology
maintain chain of custody
blood for purposes of identity
serology - standard analysis
dna
toxicology - alcohol, drug analysis
pathology - diseases
paternatiy you are not the father