Crime Scene Forensics,LLC
Blood Stains
Examining and Documenting Blood Stain Patterns
Bloodstain Pattern Analysis: is the examination of the shapes,
locations, and distribution of patterns of bloodstains, in order to provide
an interpretation of the physical events that gave rise to their origin.
The following Information may be obtained from a
proper Bloodstain Pattern Analysis:

1. Distance from the blood source to the target
2. Direction of travel and impact angles
3. Nature of the force used to cause the bloodshed
4. The object used to cause the bloodshed
5. Sequencing of multiple bloodshed events
6.Interpretation of contact or transfer patterns
When properly documented, bloodstain patterns found at the crime scene, or on a
particular person's clothing, can be used to:
1. Confirm or refute the position of a victim, witness, suspect, or defendant
2. Determine if there is evidence of a struggle, or if the assault is "one sided"
3. Confirm or refute statements made by principles in the case:
      IE: Are stain patterns on a particular person's clothing consistent
           with accounts given by the victim, witness, or defendant?
Blood Flight Characteristics:

Blood will not break up unless it is acted upon by force. The force must be great enough to
overcome the surface tension of the blood

Blood forms a spherical shape (perfect circular shape) almost immediately upon separating
from the blood source. The spherical shape is caused by the surface tension of the blood.

Surface Tension causes the blood drop to pull itself in; both horizontally and vertically.
The blood drop will settle into a spherical shape,
as a result of the surface tension.

The surface tension will maintain the sphere
shape of the blood drop until it impacts with the
surface.
For a complete list of bloodstain pattern terms, as recommended by the Internation Association of
Blood Stain Pattern Analysts. (IABPA), go to:  http://www.iabpa.org/ These terms should serve as a
guide, for those who work and teach in the field of Blood Stain Pattern Analysis. These terms are not
meant to be all encompassing.
The fascinating
world of forensic
science...made
simple
SPATTER VS TRANSFER: The simplest type of blood spatter analysis is determining
spatters from transfers. Spatters are created when blood is acted upon by force, and
travels through the air before landing on a target surface. Transfers occur when a blood
source comes in direct contact with a target surface area.
Transfer - Swipe Pattern
Transfer - Wipe Pattern
TARGET SURFACE TEXTURE:

  • Bloodstains can occur on a variety of surfaces. The type of
    surface that the blood strikes affects the amount of
    resulting spatter, including the size and appearance of the
    blood drops.
  • Blood drops on a smooth surface will make a more uniform
    or regular circular shape.
  • Blood drops on a rough surface will make an irregular
    shaped stain with rough or jagged edges.
IMPACT SPATTERS: are a random pattern of spatter of varying sizes
Spatter Pattern
LOW FORCE (VELOCITY) IMPACT SPATTER:

  • Blood that falls at the speed or force of normal gravity
  • These spatters usually fall from an open wound, or from a
    surface that is saturated with blood
  • The majority of the Low Force Impact Spatters are large,
    circular, spatters with diameters of 4mm or more
  • Low Force Impact Spatters will increase in size as the
    distance fallen increases, however, the size of the spatters
    will remain constant after approx 4 feet
  • Free falling blood has a terminal velocity of 5 to 25 feet per
    second

                                                                  
MEDIUM FORCE (VELOCITY) IMPACTSPATTER:

  • Produced with more energy or force than gravity
  • The force of the impact causes the blood to break into
    smaller size spatters  relative to the amount of  force
  • This type of spatter is usually seen in blunt force, stabbings,
    and secondary spatters
  • Produced when the majority of larger drops of blood are
    broken into smaller spatters with diameters of 2 – 4 mm
  • The force associated with this type of spatter is greater than
    25 ft per second                        
HIGH FORCE (VELOCITY) IMPACT SPATTER:

  • Impact spatter that measures less than 2mm in
    diameter
  • The force necessary to produce this size spatter
    is greater than 100 ft per second
  • This type of spatter is usually associated with
    gunshots, explosions, and high speed collisions
  • High Force Impact Spatter takes on a "mist like"
    appearance
It is important to note that the term "Velocity" does not measure the speed at which the blood is
traveling, but rather is used to describe or measure amount of force applied to the blood, to cause it
to spatter.
Direction:
The "tail" points to the direction of
the blood drop
Angle of Impact:  
The steeper the impact, the more
elliptical or elongated, the blood drop
spatter, and then dividing the width by the length (as shown) When calculating the
angle of impact, do not measure the “tail” • – it is a secondary force or event.
  • Measure the width and the length of the stain/spatter                                        
       sine=  width    =   9mm             
                 length   =  18mm
  • Always divide the smaller number by the larger number
  • Always want a number less than one
  • Arcsine 0.500 = 30 degree angle of impact
BACK SPATTER OR "BLOWBACK"

  • When a bullet strikes a target, some high
   force impact spatter may be directed back
   toward the gun that fired the shot. This is
   known as "back spatter"  
  • If the bullet exits its target, a larger
    amount of high force impact spatter may
    be directed in the same direction as the
    bullet. This is known as "forward spatter".
The amount of high force impact spatter created will depend upon the size or caliber of the bullet
fired, as well as the distance from the gun to the target. The larger the bullet, or projectile, the
greater the spatter. The closer to the target that the gun is fired...the great the spatter.