BLOODSTAIN PATTERN ANALYSIS TUTORIAL

The success or failure of any criminal investigation often depends on the recognition of physical evidence left at a crime scene and the proper analysis of that evidence.

Crime scenes that involve bloodshed often contain a wealth of information in the form of bloodstains. The pattern, size, shape, and the location of such stains may be very useful in the reconstruction of the events that occurred.

William G. ECKERT and Stuart H. JAMES

Bloodstain Pattern Analysis: is 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.

Based on the premise that all bloodstains and bloodstain patterns
are characteristic of the forces that have created them.

The determinations made from bloodstain patterns at the scene or from the clothing
of principals in a case can be used to:

nConfirm or refute assumptions concerning events and their sequence:
Position of victim. (standing, sitting, lying)
Evidence of a struggle. (blood smears, blood trails)

nConfirm or refute statements made by principals in the case:
Are stain patterns on a suspects clothing consistent with his reported actions?
Are stain patterns on a victim or at a scene consistent with accounts given by witnesses or the suspect?

Properties of Blood

Blood Volume

On average, accounts for 8 % of total body weight
n5 to 6 liters of blood for males

n4 to 5 liters of blood for females

A 40 percent blood volume loss, internally or/and externally,
is required to produce irreversible shock (death).
A blood loss of 1.5 liters, internally or externally, is required to cause incapacitation.

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.
The cohesive forces tend to resist penetration and separation.

Categories of Bloodstains

PASSIVE

TRANSFER

PROJECTED

TRANSFER BLOODSTAINS

A transfer bloodstain is created when a wet, bloody surface comes in contact with a secondary surface.

A recognizable image of all or a portion of the original surface may be observed in the pattern,
as in the case of a bloody hand or footwear.

Transfer bloodstains can be further subdivided into;

nContact bleeding

nSwipe or Smear

nWipe

nSmudge

PASSIVE BLOODSTAINS

Passive Bloodstains are drops created or formed by the force of gravity acting alone.



This category can be further subdivided to include;

nDrops

nDrip patterns

nPools

nClots

TARGET SURFACE TEXTURE
Bloodstains can occur on a variety of surfaces, such as carpet, wood, tile, wallpaper,
clothing, and the list goes on……

The type of surface the blood strikes affects the amount of resulting spatter,
including the size and appearance of the blood drops.

Blood droplets that strike a hard smooth surface, like a piece of glass, will have little or no distortion around the edge.

Blood droplets that strike linoleum flooring take on a slightly different appearance. Notice the distortion (scalloping) around the edge of the blood droplets.

Surfaces such as wood or concrete are distorted to a larger extent. Notice the spines
and secondary spatter present.



LARGE VOLUMES OF BLOOD (patterns created by same volume of blood,
from same source to target distance)

"Dripped Blood"

"Spilled Blood"

"Projected Blood" (through syringe)

PROJECTED BLOODSTAINS

Projected bloodstains are created when an exposed blood source is subjected to an action or force, greater than the force of gravity. (Internally or Externally produced)

The size, shape, and number of resulting stains will depend, primarily, on the amount of force utilized to strike the blood source.

This category can be further subdivided to include;

§*Arterial Spurt / Gush

Bloodstain pattern(s) resulting from blood exiting the body under pressure from a breached artery:

§*Cast-off Stains

Blood released or thrown from a blood-bearing object in motion:

*Impact Spatter

Blood stain patterns created when a blood source receives a blow or force resulting in the random dispersion of smaller drops of blood.

This category can be further subdivided into;

•Low Velocity

Gravitational pull up to 5 feet/sec.

Relatively large stains 4mm in size and greater

•Medium Velocity

Force of 5 to 25 feet/sec.

Preponderant stain size 1 to 4mm in size

High Velocity

Force of 100 feet/sec. and greater
Preponderant stain size 1mm in size and smaller
Mist like appearance

DIRECTIONALITY OF BLOODSTAINS

When a droplet of blood strikes a surface perpendicular (90 degrees) the resulting bloodstain will be circular.
That being the length and width of the stain will be equal.

Blood that strikes a surface at an angle less than 90 degrees will be elongated or have a tear drop shape.
Directionality is usually obvious as the pointed end of the bloodstain ( tail ) will always
point in the direction of travel.

IMPACT ANGLE DETERMINATION
ANGLE of IMPACT is the acute angle formed between the direction of the blood drop
and the plane of the surface it strikes

By utilizing trigonometric functions its possible to determine the impact angle for any given blood droplet.

SIN 0 = opp (a)

              hyp (c)

By accurately measuring the length and width of a bloodstain, the impact angle
can be calculated using the SIN formula below

SIN < = Width (a) 1.5cm

              Length (c) 3.0cm

Width (a) 1.5cm = SIN <

Length (c) 3.0cm

0.5 = SIN <

< = 30 degrees

POINT OF CONVERGENCE AND ORIGIN DETERMINATION

The common point, on a 2 dimensional surface, over which the directionality
of several bloodstains can be retraced.

Once the directionality of a group of stains has been determined,
it's possible to determine a two dimensional point or area for the group of stains.

By drawing a line through the long axis of a group of bloodstains the point of convergence
can be determined. Where the lines of the group of stains intersect one another
the convergence point can be established.

THREE DIMENSIONAL POINT OF ORIGIN DETERMINATION WITH IMPACT ANGLE CALCULATIONS

USE OF THE COMPUTER FOR POINT OF ORIGIN CALCULATIONS