Ch 10 - Bloodstain Pattern Analysis

General Features of Bloodstain Formation

• direction from which the blood originated

• angle at which a blood droplet struck a surface

• location/position of victim at the time the wound was inflicted

• movement of a bleeding individual at the crime scene

• minimum number of blows that struck a bleeding victim

• approximate location of an individual delivering blows

Surface Texture

comparisons of patterns are only valid when identical surfaces are used

• harder and nonporous surfaces result in less spatter

• rough surfaces usually result in irregularly shaped stains with serrated edges

Satellite Spatter

• blood spatter around parent stain, with blood droplets whose pointed ends face against the direction of travel

Direction and Angle of Impact

• as a stain becomes more elliptical in shape, pointed end faces its direction of travel

• distorted or disrupted edge of an elongated stain indicates the direction of travel of the blood drop

  • satellite spatter pointed end will face against the direction of travel

Angle of Impact

the angle of the source of the blood to the surface where it was deposited

• can be estimated from width-to-length ratio

  • degree of circular distortion

Drop deposited at 90 degrees

• approx. circular in shape w/ no tail or buildup of blood

Impact Spatter

produced when an object makes forceful contact with a source of blood, projecting droplets outward from the source

• consists of many droplets radiating in direct lines from the origin of blood

• classification system based on velocity

Forward Spatter

blood that travels away from the source in the same direction as the force that caused the spatter

• E.g. exit wound

Back Spatter

blood directed back toward the source of the force that caused the spatter

• potentially deposited on the object or person who created the impact

• e.g. entrance wound

Low Velocity Spatter

created by a force traveling at 5ft/sec or less; drops with a diameter of greater than 4 mm

• large, separate, or compounded drops

• nromall produced by gravity alone, by minimal force, or by object dropping into blood pool

Medium Velocity Spatter

created by a force traveling at 5 to 25 ft/sec; drops with diameters between 1 and 4 mm

• small drops

• blunt force trauma

High Velocity Spatter

created by a force traveling at 100 ft/sec or faster; droplets with diameters of less than 1 mm

• very fine droplets

• gunshot exit wounds or explosions

• may not travel very far

Area of Convergence

point on a 2D plane from which blood drops originated

Area of Origin

area in a 3D space from which the blood was projected

• will show position of victim or suspect

• indication of distance from blood source to bloodstained surface

Gunshot Spatter

• characterized by both forward and back spatter

• location of injury, size of wound, and distance between victim and muzzle all affect amount of back spatter

  • “Drawback effect” and back spatter into muzzle of gun

Cast-off Pattern

created when blood is flung from blood-bearing object in motion onto a surface

• bloodstains will point in the direction the object was moving

• width may suggest the kind of object

• may show minimum number of blows

Arterial Spray

created when victim suffers from an injury to a main artery or the heart

• large spurted stains for each time the heart pumps

• victim movement

• vertical arcs show fluctuations in BP

Expirated Blood Patterns

blood expelled by the mouth or nose from an internal injury

• may be lighter in color

Void

when an object blocks the deposition of blood spatter on a surface/object

• may give a clue as to the size or shape of missing object/person

• may help establish body position of victim or assailant

Transfer Pattern

when an object w/ blood on it touches another object that did not have blood on it

• footprints/footwear prints

  • indication of direction of travel

  • indications speed of travel

Swipe Patterns

movement of a bloody object across a surface

• will lighten and “feather” as the pattern moves

  • “feathering” also indicates amount of pressure being applied to the surface

Flows

formed by the movement of small or large amounts of blood as a result of gravity’s pull

• single drops or large volumes of blood

• direction may show movements of objects or bodies

  • either while the flow was still in progress or AFTER the blood had dried

Pool

when blood collects in a level and undisturbed place

Skeletonization

process by which edges of a bloodstain dry to the surface in a specific period of time

• will remain apparent even after the rest of the bloodstain has been disturbed from the original position

Drip Trail Pattern

series of drops that is separate from other patterns; formed by blood dripping off an object or injury

• shows movement or provides blood ID

• shape can help determine speed at which person was moving

• tails indicate direction of movement

Grid Method

setting up a grid of squares of known dimensions over the entire bloodstain pattern

Perimeter Ruler Method

setting up a rectangular border of rulers around the pattern