Forensic Characterization of Bloodstains

Bloodstain Pattern Analysis Terms

• Spatter – Bloodstains created from the application of force to the area where the blood originated.

• Origin/Source – The place from where the blood spatter came from or originated.

• Angle of Impact – The angle at which a blood droplet strikes a surface.

Parent Drop

Spines

Satellite Spatters• 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.

• 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

Blood Droplet Volume

A droplet contains approximately 0.05 cc of fluid.

Is not the same for all blood droplets, but is generally from 0.03 cc to 0.15 cc

Is directly dependent upon the surface or orifice from which it originates

The impact area is called the target.

Bloodstain 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

Backspatter—blood that is directed back toward the source of energy

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

Bloodstain Terminology, continued

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

Bloodstain Patterns

The harder and less porous the surface, the less the blood drop will break apart.

The softer and more porous the surface, the more the blood drop will break apart.

The pointed end of the bloodstain faces the direction of travel.

Types of Cast off Stains

• Drip: falls away from the object or blood source, very round in shape, found at Nicole Simpsons condo

• Swing: Falls off the weapon as it is in motion toward the target (unless backswing). Round linear pattern with the drops being close to the same size

• Cessation – falls off the weapon after it strikes the target – away from the target ALWAYS!!

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:

Bloodstain Terminology, continued

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

Terminal velocity—the greatest speed to which a free-falling drop of blood can accelerate in air. It is dependent upon the acceleration of gravity and the friction of the air against the blood—approximately 25.1 feet/second.

• High velocity—greater than 25 feet per second, usually 100 feet per second; gives a fine mist appearance• Medium velocity—5 to 25 feet per second• Low velocity—5 feet per second or less

3 Types of Arterial Blood Spatters

• Gush – similar size drops/ the linear pattern is usually horizontal unless the victim is falling.

• Spurt – similar size drops with spacing between them. Linear pattern going up and down.

• Rain – blood mess (artery is completely severed)

Non-Impact Spatters

• Blockage – absence of a stain where there should be one• Simple direct transfer – laying something down or

stepping into something• Wipe – non-bloodied surface rubs across a bloodied one

(The most blood is where you first touched it.)• Swipe – bloodied surface rubs against (or across) a non-

bloodied one. (The most blood is where you LAST touched it.)

• Smudge – when a moving object passes through a blood stain. (Hard to identify)

Impact

The more acute the angle of impact, the more elongated the stain.

90-degree angles are perfectly round drops; 80-degree angles take on a more elliptical shape.

At about 30 degrees the stain will begin to produce a tail.

The more acute the angle, the easier it is to determine the direction of travel.

Types of impact spatters

• Gunshot – mist, small drops, very elongated (Distinct area of convergence)

• Blunt object – no mist, small drops, more cylindrical

• Exhalation – mist, can look like gunshot (Cough, breath)

Area of Intersection and Convergence

The location of the blood source can be determined by drawing lines from the various blood droplets to the point where they intersect.

The area of convergence is the point of origin—the spot where the “blow” occurred. It may be established at the scene by measurement of angles with the use of strings.

String Reconstruction

• Only with impact spatters• Can assist with reconstruction• Can reveal origin of force