questions answered by blood spatter interpretation the distance between the target surface and the...

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?

Passive Bloodstains Patterns created from the force of gravity Drop, series of drops, flow patterns, blood pools, etc.

• 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.

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

Types of Bloodstain Patterns

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.

Determining Distance Blood Falls

Blood drops fall as small spheres

Blood Spatter > Distance


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



Faster drop = smaller 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…

The distance a drop has fallen cannot be measured.


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.


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 Spatter

Gravitational pull up to 5 feet/sec.

Relatively large stains 4mm in size and greater

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 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. and

greaterPreponderant stain size 1mm in size and smaller Mist like appearance

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

Types of SpatterGunshot 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.


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

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

Determining Direction of Blood

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

Blood Spatter > Direction


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



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

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



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:

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


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.

Blood Spatter/Other Types

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

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.

Blood Spatter

questions answered by blood spatter interpretation the distance between the target surface and the...

Documents