Blood Pattern Analysis

Nature of Blood

Fluid mixture:

• cellular components - 45% of blood volume

• plasma - remaining 55%

5-6 L for males

4-5 L for females

40% blood loss results in death

Bloodstain pattern analysis

application of science and known principles of liquid in motion to defining and analyzing bloodstains within the scene

Bloodstain

a deposit of blood on a surface

Bloodstain pattern

a grouping or distribution of bloodstains that indicate through regular or repetitive form, order, or arrangement the manner in which the pattern was deposited

Spatter Stain

a bloodstain resulting from a blood drop dispersed through the air due to an external force applied to a source of liquid blood

Goals of BPA

• type of pattern

• points of origin of blood

• distance of bloodstain from target

• type and direction of impact that produced the bloodshed

• speed with which blood left its source

• position of victim and/or object

• movement of victim and/or object

• number of blows/shots and/or the dispersal of blood

Splatter

is random and unorganized

to splash and scatter upon impact

Spatter

predictable and consistent

to scatter or dash in small particles or drops

Low Velocity

• relatively large stains

• 4mm in size and greater

• gravitational pull up to 5 feet/sec

Medium Velocity

• preponderant stain 1 to 4 mm in size

• force of 5 to 25 feet/sec

High Velocity

• preponderant stain size of 1 mm or greater

• force of 100 feet/sec or greater

Blood Spatter

based on the theory that blood is a fluid that will act predictably.

spatter occurs once wounds bleed.

first blows do not bleed: so if there are 3 blood marks, the victim had to be hit at least 4 times

Variables in BPA

• drop size

• angle of impact (AOI)

• height

• velocity

• surface

• clotting factors

• viscosity

Surface Tension

adhesive forces cause the droplet to take on the most energy efficient shape as it falls due to gravity, a sphere

Blood Droplet Volume

a droplet contains approximately 0.05 cc of fluid.

not the same for all blood droplets, but is generally from 0.03 cc to 0.15 cc. 

directly dependent upon the surface or orifice from which it originates

Target

the impact area of a blood droplet

Passive - Blood Pattern

From gravity acting on an injured person or object: drops, flows, pools.

• released from either a person or an object

• shape is dependent on if the object or person was moving

• generally a circular stain

Angle of Impact (AOI)

the acute angle formed between the direction of the blood drop and the plane of the surface it strikes.

• the more acute the AOI, the more elongated the stain

• 90 degree angles are perfectly round drops

• 80 degree angles take a more elliptical shape

• 30 degrees the stain will begin to produce a tail

Calculating AOI 

AOI = SIN-1(W/L)

Satellite Spatter

• smaller drops that appear around a parent drop

• generally seen in higher impact stains

• can also be from blood dropping into blood

2 types:

• attached-spike

• removed-satellite

Directionality

• direction of movement in relation to a target

• need large amount of blood

• utilizes the tail of the parent drop

Transfer Stain

bloodstain resulting from contact between a blood-bearing surface and another surface

Swipe

from a stain object to a non stained object

Wipe

something moving through the blood

Cast Off Directionality

• bounces when impacting

• the resulting drop ai in determining the direction

• angle and velocity causes excess blood to keep moving

Cast Off

blood released from an object in motion

• minimum number of blows

• not just from weapons

Swing Cast Off

flung from swinging weapons

• makes an arc that mirrors the swing

• light and long weapons will make more cast off

Cessation Cast Off

when a bloodied object comes to an abrupt halt.

often an indication of the weapon

Arterial Spurt

pattern from blood leaving an artery.

• continuous blood in larger amounts

• under more pressure than other vesicles

• can determine victims movement after injury

• systolic - heart pump

• diastolic - between pumps

Misting

blood reduced to a fine spray due to amount of energy involved.

• gunshots

• high-velocity impact

• can be affected by wind

Expectorate Spatter

blood is an irritant in the respiratory tract.

• expelled from mouth; sneezing, coughing after wounded

• often confused with misting

Expiration Pattern

projected bloodstain pattern resulting from blood forced by airflow out of the nose, mouth, or a wound

Ghosting

when something is removed from a blood covered area

Void

absence of blood in an otherwise continuous bloodstain pattern

PABS

Physiologically altered bloodstains

• when mixed with other bodily fluids

Altered Bloodstains

Clotted blood:

• absorbent materials

• in assaults

Insects:

• small 0.1-0.2mm

• ingestion and larvae

Flow of Blood

• tells orientation of an object after blood was applied

• can show if something, or someone was moved

Point of Convergence

• general are of origin

Area of Convergence

uses the point of origin of each individual stain

• determines the location of the blood source

Surface Characteristics

different surfaces result in different stain patterns

• hard, non-porous, smooth = less spatter

• rough = irregular shape with serrated edges

• porous = more satellites and spikes