Bloodstain Pattern Analysis

Forensic Skills

• You need a variety of skills in order to be able to accurately interpret bloodstain patterns including:
• Knowledge of biology and how blood behaves in the body, as it exits the body and outside the body
• Ability to systematically document the evidence with photographs and scale drawings
• Knowledge of the physics of motion
• Good spatial reasoning and pattern recognition
• Math skills, most importantly trigonometry

Bloodstain Pattern Analysis

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• What kinds information can we infer from the patterns of bloodstains found at crime scenes?

Bloodstain Pattern Analysis

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• What do you think are the main goals of BPA?

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• What kinds of questions can we attempt to answer using BPA?

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• What is the role of BPA in crime scene reconstruction?

Bloodstain Pattern Analysis

• Did a crime occur?
• Where did the crime occur?
• Was there an altercation and if so, what were the dynamics?
• What kind of injury did a victim sustain?
• Does the blood prove that a particular suspect was/was not involved?

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Interpreting Bloodstain Patterns

• What direction did the blood come from?
• At what angle did the blood strike a surface?
• Did the suspect or victim move, leaving a trail of blood?
• What was the location/position of the body (standing, seated, kneeling, etc.)?
• If the victim was struck, how many times? Was the suspect left or right handed?
• Where was the suspect standing? In front, behind, or to the side of the victime?

Typical Bloodstain Patterns

WARNING

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DO NOT, under any circumstances, use the term “blood SPLATTER.” It’s not a thing!!!

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Say it with me now:

“BLOOD SPATTER”

BPA Resource for Lab

Great resource for info on the career, preferred terminology, training, and SOPs.

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http://www.swgstain.org/Home

Drip Stains

• Result from blood falling from a stationary object→ PASSIVE BLOODSTAIN
• The only force acting on the blood is gravity.
• Ex. Blood running down a victim’s arm and dropping on to the floor, blood dripping from a table top where the suspect dropped a bloody weapon.

Drip Stains

• A drop trail can show the direction a suspect/victim was moving in as they were bleeding/carrying a bloody object.
• Tails of the drops point in the direction the person was moving.

Satellite Stains

• A smaller bloodstain that originated during the formation of the parent stain as a result of blood impacting a surface.

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Angle of Impact

• Due to its surface tension, blood forms spherical drops as it travels through the air.

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• The shape of the stain once it strikes a surface depends on the ANGLE OF IMPACT and also the TYPE OF SURFACE.

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• The ANGLE OF IMPACT is the acute angle, relative to the plane of a target, at which a blood drop strikes the target.

Angle of Impact

• A drop that falls at a 90 degree angle to the surface will form a circular pattern.

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• The larger the diameter, the higher the drop origin.

Angle of Impact

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• The width and height of a blood drop can be used to determine the angle of impact.

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• The angle of impact is calculated using the following formula:

sin< = width / length

< = sin^-1 (width / length)

Impact Patterns

• Result from a forceful impact that will project the blood in a direction away from the source

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• FORWARD SPATTER: travels in the same direction and the force

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• BACKSPATTER: travels back toward the source of the force

Impact Spatter

• Low Velocity: gravity, minimal force, splashing
• Results in large, separate drops, generally greater than 4 mm

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• Medium Velocity: blunt force traumas or moderate forces
• Results in small drops, generally 1-4 mm

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• High Velocity: Gunshot wounds, explosives
• Results in very fine droplets, generally less than 1 mm, that may not travel far

Impact Spatter

• Low Velocity

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• Medium Velocity

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• High Velocity

Cast-off Patterns

• Blood that is flung from an object as it moves
• Classified as a PROJECTED BLOODSTAIN
• Bloodstain tails point in the direction of the force
• Ex. Swinging a bat, knife, hammer, sword

Cast-off Patterns

• The size of the blood droplets can provide lots of evidence useful for crime scene reconstruction:
• What was the weapon?
• Larger droplets imply a larger source
• Droplets in a neat line came from a small object (like the tip of a knife)
• Droplets with a wider pattern came from a large or blunt object.
• What is the minimum number of blows?

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Arterial Spray Spatter

• The heart and main arteries contain blood that is under high pressure.

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• Severing one of these arteries or damaging the heart itself can cause spray patterns on nearby surfaces.

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• PROJECTED BLOODSTAIN

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• Each time the heart beats,

a new spurt erupts

Expirated Blood Patterns

• Expirated blood is coughed up or expelled from the nose or mouth in response to certain internal injuries

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• May contain air bubbles

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• Varies depending on the velocity as it exits the body (cough, wheeze, normal breath)

Void Pattern

• If there is blood spatter all around an area that is clean, it tells us that most likely there was an object there the shielded the area from the spatter.

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• May establish body position of the victim or suspect or objects that have been taken from the room.

Transfer Stains

• Transfer patterns called “swipes” occur when a bloodied object comes in contact with a surface and drags across it.

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• Similarly, the blood can already be present and the object can smear or drag through it, which is know as a “wipe”.

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• Ex. Hand prints, signs of trying to clean up

Swipe or Wipe?

Flows and Pools

• Both patterns made from moderate to large amounts of blood in response to gravity → PASSIVE BLOODSTAINS

Other Patterns

• Insect stains- Bloodstains resulting from insects landing on a bloody surface and then landing on a clean surface, transferring blood to that surface

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• Saturation stains- When blood accumulates on and then soaks into an absorbant surface

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Area of Convergence �vs.�Point of Origin

Area of Convergence

• Area where the lines drawn back from the long axis of different stains all intersect

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• Shows the general area in 2D space where the blood originated.

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• Estimate, not a precise measure

Area of Origin

• Use trigonometry to calculate in 3D where the blood spatter came from

BPA Lab

• Tomorrow - Monday (3 days in the lab)

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• Due Tues Feb. 21

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• 10 pts Extra Credit if you turn it in

Fri 02/17!