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.