Blood Spatter Interpretation
Theory and Methodology
Copyright by: Louis L. Akin, LPI
Theory: Tear drops or Sphere drops?

Experimenters
have found that
liquids of the
consistency of
blood or water
tend to form
spheres not
tears as they
separate to
drop size.
A sphere of blood in the air and as it
strikes a flat surface.
90
A
O
a
Diameter
H
Wave Cast Off
90
O
A sphere of blood traveling through the air will maintain its basic
shape until it strikes a surface at which time its lower portion will
adhere to the surface while the upper portion continues to move
forward in accord with Newton’s laws of physics (A body in motion
tends to stay in motion…) which may cause a wave to form on top
and result in a wave cast off.
The wave cast off can be seen in front of the main stain
and tells us the directionality of the spatter.
Wave Cast off
Diameter
=
Width
Low Velocity from walking bleeder
Note the cast off drop in front of the main drop.
These are called exclamation point stains. The
blood drops point the direction of travel
Calculating the Angle of Incidence
3mm
1.5 mm


Dividing the width of the stain by the length of the stain will give a
ratio:
For instance: 1.5mm / 3mm = .5 ratio.
The inverse sine of that ratio in degrees is 30 which equals the
angle of incidence or the angle at which the droplet struck the
surface.
The Central Axis
Central Axis
Direction of Travel
Length
The central axis is the longitudinal axis of the stain. An imaginary
line drawn from the cast off stain through the main stain will point to
where the blood originated or Point of Origin. It is the opposite of
the direction of travel.
Wound Exit Patterns
Blood tends to exit a wound in a cone shape pattern which
results in a round pattern against a vertical surface like a wall ,
or in a elongated oval pattern on a horizontal surface like a
table top or the floor.
The Point of Convergence
Point or Area of Convergence
on 2D (X-Y) Axis.
Y Axis
X Axis
The lines drawn through several blood stains will converge at an
area. There may be different points of convergence for each blood
letting or each blow delivered. The patterns may overlay. This gives
an X and Y axis.
The Z Axis
Z Axis Z Axis
Inside wall
Y Axis
Floor
90
X
The Y axis is a continuation of the central axis. The X axis runs
perpendicular to the Y axis at the point of convergence. The Z
axis is an imaginary line extended from the floor straight up.
Point of Origin on the Z Axis
Z
Inside wall of room
with blood spatter on
floor and wall.
POHm
Y
X
POC
By placing the strings at the angles at which the blood
stains struck the floor and wall, the lines will converge
again on the Z axis revealing the point of origin.
The Z Axis Calculation
The fluorescent strings on the floor converge at the base of the
upright Z axis. The strings going to the upright Z axis converge at
the point of origin or hemorrhage.
Cast Off Blood
90
70
40
50
70
Cast off blood is blood that is flung off a weapon
Velocities

Blood spatter was originally classified in three
velocities. Velocities are no longer stressed in
pattern interpretation, but it’s good to know
them.
 Slow velocity results from the pull of gravity
 Medium velocity results from an object that
was traveling between 5 and 25 fps such as a
fist or blunt object.
 High velocity results from an object traveling
at 100 fps or faster such as a bullet.
Low Velocity Spatter
Low velocity spatter or drops freefall as a
result of gravity. They are not projected.
Low Velocity with Void
Medium velocity caused by blunt or sharp instrument trauma.
Meduium to High Velocity
High Velocity blood
may appear as a fine
spray or mist. It may
result from a gunshot,
explosives, industrial
machinery, or even
coughing or sneezing.
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
Cartridge
2
Cartridge 1
Bullet Hole
Akin Investigations, Austin TX