Blood Stain Patterns

Introductory Material

• The shape and location of bloodstains provide clues to where the crime happened and the movement of the suspect and the victim.

• Blood also reveals disease, drugs, alcohol, and identity of a victim and/or the suspect

Bloodstain Pattern Analysis

• Examination of the shapes, locations, and distribution of bloodstains in order to provide information on the physical events that are the origin of the stains

• Holding true that all bloodstains and patterns are characteristic of the forces that have created them

Information from bloodstain patterns• Origin of blood• Type of instrument

causing the stain• Direction of strike on

victim• Relative position of

victim, assailant (s), and bystanders

• Movement of victim and assailant during attack

• Number of strikes on victim

• Truthfulness of suspects and witnesses

Surface Texture

• Soft, porous surfaces provide good blood spatters

• The harder and less porous the surface, the less of a spatter will be present

Directions

• You can tell the direction of blood’s travel by the shape of the spatter. The pointed end of the spatter is the direction of travel.

• You can determine the angle of impact by measuring the degree of circular distortion. At a right angle, a blood drop will create a circular pattern, the lesser the angle, the more elongated the spatter is

Determine axis

• The origin of a spatter can be obtained by drawing straight lines through the widest and longest part of the spatter. The intersection or point of convergence is the point of origin for the spatter.

Determine Angle of Impact

• Using trigonometric ratio of sin = opp/hyp

• Sin= width/length

• Width(1.5cm)/Length(3.0cm) = sin

• Sin = 0.5

• Angle = 30

Angle of Impact“The tail tells the tale”

• 90 degrees –

• 60 degrees –

• 30 degrees –

• 10 degrees –

What does trigonometry prove?• Confirms or refutes:

– Position of victim (sitting, standing, lying)– Evidence of struggle (blood smears, blood

trails)

• Confirms or refutes:– If stain patterns are in accordance with

statements given by suspects or witnesses– If stain patterns on clothing of suspect are

consistent with reported action of suspect

Point of Convergence

• A common point on a 2-D surface over which several bloodstains can be retracted

Blood Behavior

• Important to understand movement and clotting

• These characteristics combine the composition of blood and the physics of liquid

Blood Behavior

• Liquid and solid • Liquid behavior

– Flows and pools– Spreads across flat surface and sticks

to containers– Viscosity- measure of thickness of

liquid– Surface tension- tendency of liquid

molecules to be attracted to one another and hold shape

Clotting

• When blood leaves the body it begins to clot

• Normal clotting time is 3-15 minutes

• Although clotting time is dependent on the individual– Dependent on

medical conditions, medications such as blood thinners

Clotting

• When blood clots, a dark shiny jelly-like mass separates from the yellowish serum

• This allows a rough time frame of how long the blood has been outside the body– Minutes- still liquid– Less than an hour- shiny gelatinous pool– Hours later- clot and serum have separated

Clotting

• Spurting or gushing blood stains occurred before death

• If spatters and splashes have not clotted and pool has, the victim was struck after death– These stains can only be caused by

an assailant

Blood Facts

• On average- 8% of body weight

• 5-6 liters in males• 4-5 liters in

females• If you lose 40% of

total volume, it results in irreversible shock and death (1.5L)

Oozing, Gushing, and Dripping…

• Each kind of blood movement leaves a specific stain

• If a person is left unchecked, exsanguination will occur (bleed to death)

Categories of Bloodstains

• Transfer

• Passive

• Projected

Transfer stain

• Bloody object comes in contact with non-bloody object– Bloody handprint,

shoe print in blood

• Subcategories:– Contact bleeding– Swipe or smear– Wipe– Smudge

Passive Stain

• Due to gravity• Blood flowing into the

lowest elevation of the crime scene

• Fast flowing blood moves far away

• Slow ooze clots close to the body

• Subcategories:– Passive drop- fall due to

gravity– Drip pattern- blood into

blood– Flow pattern- downhill

or due to object

Projected Stain

• Energy source applied to blood

• Several variations

Projected Stain• Low Velocity Impact

Spatter (LVIS)- low impact to blood source

• Medium Velocity Impact Spatter (MVIS)- medium force, usually from beating

• High Velocity Impact Spatter (HVIS)- high force, usually from gunshot or heavy machinery

• Cast-Off Pattern- blood is released or thrown from a blood bearing object in motion

Projected Stain

• Arterial Spurting Pattern- blood exiting the body under pressure from a breached artery

• Back spatter- blood directed back towards energy source

• Expiratory Blood- Blood blown out of nose, mouth or wound due to air pressure

Void Pattern

• Absence of blood spatter where you would expect one to be

• Often results from the position of the assailant

• Spatter occurs around the position of the attacker

Blood Spatter on Clothes

• If spatter is on clothes then the person was present at the time of the incident

• If no spatter, but smear or smudge, then the person was not present when blood was sprayed, but came in contact with blood after the incident