Post on 08-Jan-2022
BLOODSTAIN PATTERN ANALYSIS
Forensic Science
Mr. Thomas
BLOODSTAIN PATTERN ANALYSIS (BPA) CAN DETERMINE
n Location and description of individual stains and patterns
n Mechanism that created the stains
n Direction a blood droplet was traveling
n Area of origin
n Type of object used in attack
n Minimum number of blows
n Presence of a subject at a scene
n Positioning of the victim, suspect and objects during events
n Sequence of events
Science Murder
Blood Spatter Video
WHAT IS BLOOD? INTRODUCTION TO BLOOD BLOOD SPATTER (OR SPLATTER)
Blood drops form different shapes and sizes
Blood spatter analysis uses the shapes and sizes to reconstruct the crime scene.
Determining Distance Blood Falls
Blood drops fall as small spheres
§ Drops form circles when hitting surface § Size depends on speed of blood drop
Faster drop = larger diameter (size) Higher distance = larger diameter
Due to air resistance, speed maxes out at distances above about 7 feet
However, size of drop also depends on the volume of the drop.
Volume depends on the object blood originated from (needle = small; bat = large).
Since the volume of blood is unknown in most cases…
The distance a drop has fallen cannot be measured.
ANGLE OF IMPACT AND POINT/AREA OF CONVERGENCE
Determining Direction of Blood
Narrow end of a blood drop will point in the direction of travel.
§ The angle can be determined mathematically.
§ Width/Length, then take the inverse sin (sin-1).
§ This number is the impact angle (90 = perpendicular to surface; <10 at a sharp angle)
n A well-formed stain is in the shape of an ellipse
n Accurately measuring the stain gives this impact angle
If more than one drop (from spatter) results, the point of origin can be determined
If more than one drop (from spatter) results, the point of origin can be determined
For each blood drop, a string can be
guided back to the point of origin.
POINT AND AREA OF CONVERGENCE
n The point of convergence is the intersection of two bloodstain paths, where the stains come from opposite sides of the impact pattern
POINT AND AREA OF CONVERGENCE
n The area of convergence is the box formed by the intersection of several stains from opposite sides of the impact pattern
TARGET SURFACE TEXTURE
§ Smooth surface = smooth sphere § Rough surface may cause some splatter
TARGET SURFACE TEXTURE TARGET SURFACE TEXTURE
n Blood droplets that strike a hard smooth surface, like a piece of glass, will have little or no distortion around the edge.
TARGET SURFACE TEXTURE
n Blood droplets that strike linoleum flooring take on a slightly different appearance.
n Notice scalloping around the edge of the blood droplets.
TARGET SURFACE TEXTURE
n Surfaces such as wood or concrete are distorted to a larger extent.
n Notice the spines and secondary spatter present.
BLOODSTAIN PATTERN CATEGORIES
BLOODSTAIN PATTERN CATEGORIES
n Classifies stains based on the mechanism that created them.
¨ Passive bloodstains are created when the force acting on the blood is gravity
¨ Projected bloodstains occur when some form of energy has been transferred to a blood source
¨ Transfer or contact is produced when an object with blood on it comes into contact with an object or a surface that does not have blood on it.
Spattered Blood
In general, for higher impacts, the pattern is more spread out and the individual stains are smaller.
Low impact = beating High impact = gunshot
PASSIVE BLOODSTAINS
PASSIVE DROP
A bloodstain drop(s) created or formed by the force of gravity acting alone
DRIP PATTERN
A bloodstain pattern that results from blood dripping into blood
FLOW PATTERN
A change in the shape and direction of a bloodstain due to the influence of gravity or movement of the object
PROJECTED BLOODSTAINS
LOW VELOCITY IMPACT (LVI)
Relatively large stains 4 mm in size and greater. Impact velocity up to 5 feet/sec
MEDIUM VELOCITY IMPACT (MVI)
Preponderant stain size 1 to 4 mm size.
Impact velocity of 5 to 25 feet/sec.
Gunshot Spatter = can result in a mist-like spatter that indicates a gunshot.
§ Not all gunshots will result in misting.
§ If misting is present, it is most likely a gunshot.
HIGH VELOCITY IMPACT (HVI) HIGH VELOCITY IMPACT (HVI)
Preponderant stain size 1 mm in size and smaller. Mist like appearance.
Impact velocity of 100 feet/sec and greater.
Gunshot Spatter
Gunshots result in back spatter (where bullet enters) and forward spatter (where bullet exits).
Types of Spatter
Beating and Stabbing Spatter = larger individual stains
First blow usually doesn’t result in spatter since there is not yet any exposed blood.
Types of Spatter
Castoff Pattern = Blood flung off of swinging object.
Can reconstruct where assailant and victim were positioned.
CAST-OFF PATTERN
Types of Spatter
Satellite Spatter = free falling drops of blood that fall onto a spatter pattern.
§ These drips are usually much larger than impact spatter.
§ However, blood dripping into blood can create a spatter.
Types of Spatter
Expirated Bloodstain Pattern = Blood can accumulate in lungs, sinuses, and airway. Forcibly exhaled.
§ Can appear like beating or gunshot pattern.
§ May be mixed with saliva or nasal secretions.
ARTERIAL SPURTING OR GUSHING
Bloodstain pattern(s) resulting from blood exiting the body under pressure from a breached artery
TRANSFER/CONTACT BLOODSTAINS
SWIPE PATTERN
The transfer of blood from a moving source onto an unstained surface. Direction of travel may be determined by the
feathered edge.
HAIR SWIPE PATTERN
The transfer of blood from a moving source onto an unstained surface. Direction of travel may be determined by the
feathered edge.
WIPE PATTERN
A bloodstain pattern created when an object moves through an existing stain, removing and/or altering its appearance.
TRANSFER PATTERN
A recognizable image of all or a portion of the original surface may be observed in the pattern.