Transcript Blood splatter analysis

History of Blood Spatter
1894 – Pitoroski wrote the earliest
reference to blood spatter
 1939 – Balthazard first researcher to
analyze the meaning of spatter pattern
 1955 – blood spatter evidence used in the
Sam Shepard case, helping to exonerate
him
 1971 – Dr. Herbert McDonnell used bloodspatter analysis as tool in forensic
examination

Blood Spatter Lecture
Blood splatter analysis
the examination of the shapes,
locations, and distribution patterns of
bloodstains, in order to provide an
interpretation of the physical events
which gave rise to their origin
• Why does a drop of blood have a curved
surface when it lands on a flat surface instead of
spreading out flat?
• Why doesn’t it separate in the air before it hits
the ground?
https://www.youtube.com/watch?v=HVT3Y3_gHGg
• Gravity: pulls it to ground
– Droplet becomes longer than wide
• Cohesion: blood mixture is attracted to
similar blood mixtures and sticks together,
not separates, as it falls
– Causes droplet to stay together
• Adhesion: attractive forces of two different
objects
– starts as teardrop because of adhesion
• Surface Tension: the elastic like property of
the surface of the liquid that makes it tend
to contract, caused by the forces of
attraction between the molecules of the
liquid.
– Formation of a sphere
Passive Blood Stains
Passive Bloodstains are drops created or
formed by the force of gravity acting alone.
Types: drips, drops, pools, and clots
Transfer Bloodstains
A transfer bloodstain is created when a wet,
bloody surface comes in contact with a
secondary surface.
Types: smear, wipe, smudges
Projected Blood Stains
 Projected bloodstains
are created when an
exposed blood source is
subjected to an action
or force, greater than
the force of gravity.
Types of Projected Blood Stains
Arterial Spurt
Cast-off Stains
Impact Slatter
Blood Loss History
•
•
Blood may be dripped out, sprayed from an
artery, oozed out through a large wound, or
flung off a weapon raised to strike another
blow.
In the 1930s, Scottish pathologist John
Glaister classified blood splashes into six
distinct types
Six Patterns Blood can be classified:
1. Passive Fall - Blood falling directly to floor
at 90-degree angle will produce circular
drops, with secondary satellites being
more produced if surface hits is textured
2. Arterial spurts or gushes – typically
found on walls or ceilings caused by
pumping action of the heart
3. Splashes – shaped like exclamation points.
– Shape and position of spatter pattern can
help locate the position of the victim at the
time of the attack
4. Smears – left by bleeding victim
depositing blood as he or she touches or
brushes against a wall or furniture
– transfers
5. Trails – can be left by bleeding victim
depositing blood as he or she moves from
one location to another.
– Can be round, smeared, appear as
spurts
6. Pools – form around victim who is
bleeding heavily and remains in one
place.
– If victim is moved to another location,
there may be droplets or smearing
connecting the first location with a
second
IMPACT of blood droplets
• Flat surface – edge of blood drop
appears smooth and circular
– Glass, marble
• Porous surface – edge of drop of
blood may form small spikes
(extensions) or satellites
– Spikes – attached to make
droplet
– Satellites – not attached to
main droplet
HEIGHT of blood droplets
• The higher the
droplet falls, the
more blood satellite
spatter occurs
• The stain diameter
will be larger as
well
VELOCITY /FORCE of blood droplets
• Velocity = meters per second (m/sec)
• Blood produced from which would travel
faster – hammer or gunshot?
• High Velocity Impact
• greater than 50 m/sec
• fine-mist or spraying spatter
patter
• Size of Droplets = less than 1
millimeter
• Injury examples: gunshot,
chainsaws, wood chippers,
etc.
• Medium Velocity Impact
• Blood moves between 5 and 50 m/sec
• Size of Droplets depends on angel of impact (long,
thin; 1- 4 mm)
• Injury examples: blunt force trauma; beating,
stabbing, baseball bats, bricks, hammers, etc.
• Low Velocity Impact
• Dripping blood (gravity), cast-off a weapon
• Dripping blood often falls at 90 angle
• Round blood stain; larger than 4 mm usually
• If object is moving, elliptical blood stains where
direction can be determined
DIRECTIONALITY of blood
• Shape provides clues to direction from
which blood originated
– Circular drop (width = length)
• Fell straight down (gravity)
• Typical of dripping or low-velocity
wound (passive)
– Elongated drop (width < length)
• Possible to determine direction
blood was traveling
• Tail points in direction blood drop
Angle of Impact
the acute angle
formed between
the direction of the
blood drop and
the plane of the
surface it strikes.
= SIN-1 (W / L)
W = Width of blood
drop
L = Length of blood
drop
Finding AOI
LENGTH = 5.9cm
WIDTH = 2.6cm
SOLUTION:
AOI =
-1
SIN
W/L
AOI = SIN-1 2.6/5.9
AOI =
-1
SIN
(.44)
AOI = 26.2°
Point of Convergence
• 2D view of the
location of the source
• can be determined if
there are at least two
drops of blood spatter.
• Lines of Convergence –
found by drawing
straight lines down the
long axis of blood
spatter and noting
where they intersect
Point of origin: helps us determine whether
the victim was lying, standing, kneeling, etc.
when they were assaulted
lies at a point in space above the point
of convergence.
Must use stains on flat surfaces (walls,
ceilings, floors, etc.)
Not quite exact (basketball-size area)
2-D image (convergence) + angle of
impact = 3-D image (point of origin).
1. Find distance from each blood stain along its
central axis to the POC (distance = y)
2. Then take the TAN of the degrees AOI.
3. Third, multiply the TAN of the AOI by the
distance.
4. Measure that distance from the floor up the
perpendicular axis and you will arrive at the
Point of Origin (PO)
FORMULA: PO = TAN (AOI) X y
Finding PO
DISTANCE FROM BLOODSTAIN (to POC): 90cm
AOI (calculated from AOI formula): 26.2°
SOLUTION:
PO = TAN (26.2) x 90
PO = .492 x 90 = 44.29 cm
What can the blood spatter tell us???
•The position of the victim and the attacker each
time blood was let
•The movements of the victim and the attacker
•The class of weapon used, i.e. firearm, blunt or
sharp instrument
•The number of blows struck