Blood Spatter AnalysisPrashant Mehta

Assistant Professor, National Law University

A field of forensic examination of the shapes, locations, and distribution patterns of bloodstains, in order to

provide an interpretation of the physical events which gave rise to their origin.

PROPERTIES OF BLOOD

• 8% of total body weight

• 5-6 liters of blood for males

• 4-5 liters of blood for females

• 40% blood volume loss,

internally or externally required

to produce death.

• 1.5 L loss will cause

incapacitation.

• A cut vein or artery will result in

a loss of ½ L per minute.

INJURIES, DEATH AND BLOOD

• Dead people do not bleed.• If a body part is struck with an object the first blow will not cause blood spatter.• Spatter occurs after the first blow when the wound begins to bleed.

SURFACE TENSION

• 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.

• Blood Surface tension is 0.058 N/m.

VISCOSITY

• Viscosity is defined as a fluid’s resistance to flow. The more viscous a substance is, the more slowly it will flow. The SI unit for viscosity is the Pascal second. Fluid viscosity is compared to water that has a viscosity of one. Blood is thicker than water and is viscous primarily due to the cellular component. Blood Viscosity is 3-4 Pascal second.

DENSITY

It is defined as mass per unit volume. The density of water is 1000 kg/m3. The density of blood is proportional to the total protein concentration or cellular component of blood and is influenced only to a minor extent by other ions, gases etc. that are dissolved in the plasma. The average density of whole blood for a human is about 1060 kg/m3.

TERMINOLOGY

• Angle of impact: angle at which blood strikes a target surface

• Bloodstain transfer: when a bloody object comes into contact with a surface and leaves a

patterned blood image on the surface

• Back-spatter: blood that is directed back toward the source of energy

• Cast-off: blood that is thrown from an object in motion

• Directionality—relates to the direction a drop of blood travels in space from its point of origin

• Contact stain: bloodstains caused by contact between a wet blood-bearing surface and a

second surface that may or may not have blood on it

Transfer—an image is recognizable and may be identifiable with a particular object

Swipe—wet blood is transferred to a surface that did not have blood on it

Wipe—a non-blood-bearing object moves through a wet bloodstain, altering the

appearance of the original stain

WHAT DOES IT TELL US?

1. Type and velocity of use of weapon

2. Number of blows

3. Handedness of assailant (right or left-handed)

4. Position and movements of the victim and assailant during and after the attack

5. Which wounds were inflicted first

6. Type of injuries

7. How long ago the crime was committed

8. Whether death was immediate or delayed

Reconstruction could tell some more..

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

DROP OF BLOOD

• Parent Drop – The droplet from which a satellite spatter originates.

• Satellite Spatters – Small drops of blood that break of from the parent spatter when the blood droplet hits a surface.

• Spines – The pointed edges of a stain that radiate out from the spatter; can help determine the direction from which the blood traveled.

tail points in direction of

travel

one exception!

Categories of Bloodstains

• Passive

• Transfer

• Projected

• 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.

PASSIVE BLOODSTAINS• Passive bloodstains are drops created or formed by the force of gravity

acting alone.• Projected bloodstains are created when an exposed blood source is subjected to

an action or force, greater than the force of gravity. (Internally or Externally produced).

• The size, shape, and number of resulting stains will depend, primarily, on the amount of force utilized to strike the blood source.

Passive Patterns:• Drops

• Drip patterns

• Pools

• Clots

Drops Drip

Clots Pool

Types of Passive Blood Stains

TRANSFER BLOODSTAINS

• A transfer bloodstain is created when a wet, bloody surface comes in contact with a secondary surface.

TYPES OF TRANSFER BLOOD STAINS

• Contact bleeding

• Swipe or smear

• Wipe / Smudge

• Back Spatter

Contact Bleeding Swipe / Smear

Wipe / Smudge Pool

Types of Transfer Blood Stains

Other Patterns

Back Spatter Transfer

PROJECTED BLOOD

• Projected bloodstains are created when an exposed blood source is subjected to an action or force, greater than the force of gravity. (Internally or externally produced.)

• The size, shape, and number of resulting stains will depend, primarily, on the amount of force utilized to strike the blood source.

Droplets could be altered..

1. Size of the droplet

2. Angle of impact

3. Velocity at which the blood droplet left its origin

4. Height

5. Texture of the target surface1. On clean glass or plastic—droplet will have smooth outside

edges

2. On a rough surface—will produce scalloping on the edges

LARGE VOLUMES OF BLOODPatterns created by same volume of blood from the same source to target distance

Dripped Blood Spilled Blood

TARGET SURFACE TEXTURE

• Bloodstains can occur on a variety of surfaces, such as carpet, wood, tile, wallpaper, clothing, etc.

• The type of surface the blood strikes affects the amount of resulting spatter including the size and appearance of the blood drops.

TARGET SURFACE TEXTURE

• 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

• Blood droplets that strike linoleum flooring take on a slightly different appearance. Notice the distortion (scalloping) around the edge of the blood

droplets.

TARGET SURFACE TEXTURE

• Surfaces such as wood or concrete are distorted to a larger extent. Notice the spines and secondary spatter present.

ARTERIAL SPURT/GUSH

• Bloodstain patterns resulting from blood exiting the body under pressure from a breached artery.

CAST-OFF STAINS

• Blood released or thrown from a blood-bearing object in motion.

IMPACT SPATTER

Blood stain patterns created when a blood source receives a blow or force

resulting in the random dispersion of smaller drops of blood. It depends on

spreading behaviour / surface texture and velocity

Stages of Drop Impact

Contact & Collapse Displacement

Image used with permission from Tom Bevel & Ross Gardner, June 2006.

Stages of Drop Impact

Dispersion Retraction

Image used with permission from Tom Bevel & Ross Gardner, June 2006.

LOW VELOCITY IMPACT SPATTER

Low velocity spatter is about 5 ft / second and usually 3 mm or greater in diameter and indicates blood is dripping. Low impact is really blood under the influence of gravity - it just falls.

MEDIUM VELOCITY IMPACT SPATTER

Medium velocity spatter is 5 – 25 ft / second with a <3 mm diameter and usually indicates blunt trauma or sharp trauma or it could be cast-off. Medium impact occurs when a force such as a bat is applied.

HIGH VELOCITY IMPACT SPATTER

Force of 100 feet/sec and greater. Preponderant stain size 1 mm in size and smaller. Mist like appearance.

DIRECTIONALITY OF BLOODSTAINS

• When a droplet of blood strikes a surface perpendicular (90 degrees) the resulting bloodstain will be circular.

• That being the length and width of the stain will be equal.

DIRECTIONALITY OF BLOODSTAINS

• Blood that strikes a surface at an angle less than 90 degrees will be elongated or have a tear drop shape.

• Directionality is usually obvious as the pointed end of the bloodstain (tail) will always point in the direction of travel.

IMPACT ANGLE DETERMINATION

• The angle of impact is the acute angle formed between the direction of the

blood drop and the plane of the surface. The more acute the angle, the

easier it is to determine the direction of travel.

• By utilizing trigonometric functions its possible to determine the impact

angle for any given blood droplet.

• SIN < = opp (a)/hyp (c)

Angle of Impact

Directionality: Impact Angle Determination

sin θ = W / L

What does W = L mean?sin θ = 1 → θ = 90Drop is a circle!

IMPACT ANGLE DETERMINATION

POINT OF CONVERGENCE AND ORIGIN DETERMINATION

• The common point, on a 2 dimensional surface, over which the directionality of several bloodstains can be retraced.

• Once the directionality of a group of stains has been determined, it’s possible to determine a two dimensional point or area for the group of stains.

POINT OF CONVERGENCE AND ORIGIN DETERMINATION

Origin Determination• The common point, on a 2 dimensional surface, over which the directionality of

several bloodstains can be retraced. • Once the directionality of a group of stains has been determined,

it's possible to determine a two dimensional point or area for the group of stains. • By drawing a line through the long axis of a group of bloodstains the point of

convergence can be determined. Where the lines of the group of stains intersect one another the convergence point can be established.

Is it Blood – Kastle Meyer Test

The Kastle-Meyer test is a presumptive blood test, first described in 1903, in which the chemical indicator phenolphthalein is used to detect the possible presence of hemoglobin.

It relies on the peroxidase-like activity of hemoglobin in blood to catalyze the oxidation of phenolphthalin (the colorless reduced form of phenolphthalein) into phenolphthalein, which is visible as a bright pink color. 

Whose Blood it is? Human / Animal

• To determine if the blood is human, it is necessary to produce anti-human antibodies. Injecting some human blood into a different animal, a rabbit for example does this. When human blood is injected into the rabbit, the rabbit produces anti-human antibodies or anti-serum.

• To perform the precipitin test, a sample of the suspected human blood in placed

in the depression of a gelatin coated depression slide. Anti-human antibodies or anti-serum if placed on the opposite side of the depression slide. After applying an electric current, the protein molecules in the two samples migrate towards each other forming a precipitin line where the proteins combine (antigen and antibodies).

Is there Hidden Blood

• When using luminol to test for blood the area of suspicion must be darkened. The luminol mixture is sprayed onto the suspect area and when the bloodstain comes into contact with the luminol there is an emission of bright blue light.

• When luminol is being used to detect blood, the catalyst for the reaction is haemoglobin. Haemoglobin is a molecule that contains iron and is found in red blood cells.

• The chemical reaction is an example of chemiluminescence.• Chemical Structure: Luminol’s (C8H7N3O2) scientific name is 5-amino-2,3-dihydro-

1,4-phthalazine-dione.