Bloodstains Pattern Analysis

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# Bloodstains Pattern Analysis - PowerPoint PPT Presentation

Bloodstains Pattern Analysis. Questions Answered by Blood Spatter Interpretation. The distance between the target surface and the origin of blood The point(s) of origin of the blood Movement and direction of a person or an object

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### Bloodstains Pattern Analysis

Questions Answered by Blood Spatter Interpretation
• The distance between the target surface and the origin of blood
• The point(s) of origin of the blood
• Movement and direction of a person or an object
• The number of blows, shots, etc. causing the bloodshed and/or the dispersal of blood.
• Type and direction of impact that produced the bloodshed
• The position of the victim and/or object during bloodshed
• Movement of the victim and/or object after bloodshed
Summary
• Establish the relationship between dropping height and blood drop diameter
• Differentiate between high velocity and medium velocity impact spatter
• Recognize patterns around the drop, such as satellite spatter or spines
• Create and examine vertical blood drop patterns on various textured surfaces
• Identify a point of convergence and point of origin
Blood Droplet Characteristics
• A blood droplet will remain spherical in space until it collides with a surface
• Once a blood droplet impacts a surface, a bloodstain is formed.
• A droplet falling from the same height, hitting the same surface at the same angle, will produce a stain with the same basic shape.
• How will the shape change as the height is increased or decreased?

Projected Bloodstains

• Patterns that occur when a force is applied to the source of the blood
• Includes low, medium, or high impact spatters, cast-off, arterial spurting, expiratory blood blown out of the nose, mouth, or wound.
• Transfer or Contact Bloodstains
• These patterns are created when a wet, bloody object comes in contact with a target surface; may be used to identify an object or body part.
• A wipe pattern is created from an object moving through a bloodstain, while a swipe pattern is created from an object leaving a bloodstain.
Types of Bloodstain Patterns
• Passive Bloodstains
• Patterns created from the force of gravity
• Drop, series of drops, flow patterns, blood pools, etc.

Images from http://www.bloodspatter.com/BPATutorial.htm

Conditions Affecting Shape of Blood Droplet
• Size of the droplet
• Angle of impact
• Velocity at which the blood droplet left its origin
• Height
• Texture of the target surface
• On clean glass or plastic—droplet will have smooth outside edges
• On a rough surface—will produce scalloping on the edges
Blood Spatter (or splatter)

Blood drops form different shapes and sizes

Blood spatter analysis uses the shapes and sizes to reconstruct the crime scene.

Blood Spatter > Distance

Determining Distance Blood Falls

Blood drops fall as small spheres

Blood Spatter > Distance

Determining Distance Blood Falls

• Drops form circle when hitting surface
• Size depends on speed of blood drop

Blood Spatter > Distance

Determining Distance Blood Falls

Faster drop = smaller diameter (size)

Higher distance = larger diameter

Due to air resistance, speed maxes out at distances above about 7 feet

Blood Spatter > Distance

Determining Distance Blood Falls

However, size of drop also depends on the volume of the drop.

Volume depends on the object blood originated from (needle = small; bat = large).

Blood Spatter > Distance

Determining Distance Blood Falls

Since the volume of blood is unknown…

The distance a drop has fallen cannot be measured.

Blood Spatter/ Velocity

Types of Spatter

• Spattered Blood = random distribution of bloodstains that vary in size
• Amount of blood and amount of force affect the size of blood spatter.
• Can result from gunshot, stabbing, beating

Blood Spatter/ Velocity

Spattered Blood can:

• Help determine the location of the origin of the blood source.
• Help determine the mechanism which created the pattern.

Blood Spatter/ Velocity

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

Impact spatter
• Results from the application of energy to a source of wet blood
• Arises from kicking, punching, or firearms
• Mist – very fine spatter (.01 mm)
• Usually a product of a gunshot
• Fine – mainly 2mm or less
• Suggestive of beating type assault
• Medium – 2mm – 6mm in diameter
• Suggestive of weapon cast off
• Large - >6mm
• Suggestive of dripping blood
• Note that sneezing or coughing could cause similar patterns as above

Low Velocity

Gravitational pull up to5 feet/sec.

Relatively large stains4mm in size and greater

Low Velocity Spatter
• Gravitational pull up to5 feet/sec.
• Relatively large stains4mm in size and greater
Medium Velocity
• Force of 5 to 25 feet/sec.
• Preponderant stain size1 to 4mm in size
• Beating and Stabbing Spatter = larger individual stains
• First blow usually doesn’t result in spatter since there is not yet any exposed blood
High Velocity
• Force of 100 feet/sec. andgreaterPreponderant stain size1mm in size and smaller Mist like appearance
• Gunshot Spatter = can result in a mist-like spatter that indicates a gunshot.

Blood Spatter/ Velocity

Gunshot Spatter = can result in a mist-like spatter that indicates a gunshot.

Types of Spatter

• Not all gunshots will result in misting.
• If misting is present, it is most likely a gunshot.

Gunshots result in back spatter (where bullet enters) and forward spatter (where bullet exits).

Blood Spatter

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.

Blood Spatter

Effect of Surface

• Smooth surface = smooth sphere
• Rough surface may cause some splatter

Blood Spatter > Direction

Determining Direction of Blood

Narrow end of a blood drop will point in the direction of travel.

Blood Spatter > Direction

Determining Direction of Blood

If more than one drop (from spatter) results, the point of origin can be determined

Blood Spatter > Direction

Determining Direction of Blood

If more than one drop (from spatter) results, the point of origin can be determined

Blood Spatter > Direction

Determining Direction of Blood

This is a 2-dimensional point of origin called point of convergence

It is possible to determine the 3-D point of origin

Blood Spatter > Direction

Determining Direction of Blood

• 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)
Bloodstain Patterns

The shape of a blood drop:

• Round—if it falls straight down at a 90 degree angle.
• Elliptical—blood droplets elongate as the angle decreases from 90 to 0 degrees; the angle can be determined by the following formula:

Blood Spatter > Direction

• For each blood drop, a string can be guided back to the point of origin.

Blood Spatter/Other Types

Other Types of Spatter

Castoff Pattern = Blood flung off of swinging object.

Can reconstruct where assailant and victim were positioned.

Blood Spatter/Other Types

Other 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 Blood
• Patterns are caused by the pressure within the arterial system
• Will depend on:
• Damage to the artery
• Site of the injury
• Presence of clothing
• Direction of spurting
• Distance of target surface
• Patterns are usually the same size
Contact
• Contact smears usually arise from contact of a bloodstained item with a non-bloodstained surface
• Can leave imprint evidence

Blood Spatter

Alteration of bloodstain over time

• Blood dries and clots over time.
• Difficult to estimate the time the blood exited the body.
• Clotted smears can indicate time of movement.