Download - Blood pattern analysis
Blood Pattern Analysis
Pre-Lab Information
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
• The elastic like property of the surface of the liquid that makes it tend to contract, caused by the forces of attraction between the molecules of the liquid.
• The cohesive forces tend to resist penetration and separation.
Categories of Bloodstains
• PASSIVE
• TRANSFER
• PROJECTED
TRANSFER BLOODSTAINS
• A transfer bloodstain is created when a wet, bloody surface comes in contact with a secondary surface.
TRANSFER STAINS SUBDIVISIONS
• CONTACT BLEEDING
• SWIPE OR SMEAR
• WIPE
• SMUDGE
PASSIVE BLOODSTAINS
• Passive bloodstains are drops created or formed by the force of gravity acting alone.
PASSIVE PATTERNS
• DROPS
• DRIP PATTERNS
• POOLS
• CLOTS
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.
LARGE VOLUMES OF BLOOD
• Patterns created by same volume of blood from the same source to target distance.
DRIPPED BLOOD
SPILLED BLOOD
PROJECTED BLOODThrough Syringe
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.)
PROJECTED BLOOD
• The size, shape, and number of resulting stains will depend, primarily, on the amount of force utilized to strike the blood source.
ARTERIAL SPURT/GUSH
• Bloodstain patterns resulting from blood exiting the body under pressure from a breached artery.
ARTERIAL SPURT/GUSH
CAST-OFF STAINS
• Blood released or thrown from a blood-bearing object in motion.
CAST-OFF STAINS
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.
LOW VELOCITY IMPACT SPATTER
• Gravitational pull of up to 5 feet/sec
• Relatively large stains 4 mm in size and greater.
LOW VELOCITY IMPACT SPATTER
MEDIUM VELOCITY IMPACT SPATTER
• Force of 5 to 25 feet/sec.
• Preponderant stain size 1 to 4 mm in size.
MEDIUM VELOCITY IMPACT SPATTER
HIGH VELOCITY IMPACT SPATTER
• Force of 100 feet/sec and greater.
• Preponderant stain size 1 mm in size and smaller.
• Mist like appearance.
HIGH VELOCITY IMPACT SPATTER
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.
DIRECTIONALITY OF BLOODSTAINS
DIRECTIONALITY OF BLOODSTAINS
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.
• By utilizing trigonometric functions its possible to determine the impact angle for any given blood droplet.
• SIN < = opp (a)/hyp (c)
IMPACT ANGLE DETERMINATION
IMPACT ANGLE DETERMINATION
• By accurately measuring the length and width of a bloodstain, the impact angle can be calculated using the Sine formula
IMPACT ANGLE DETERMINATION
IMPACT ANGLE DETERMINATION
• SIN < = width (a) 1.5 cm/length (c) 3.0 cm
• 0.5 = SIN <• < = 30 degrees.
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
POINT OF CONVERGENCE AND ORIGIN DETERMINATION
POINT OF CONVERGENCE AND ORIGIN DETERMINATION
VOIDS
• Void in otherwise uniform splatter - something blocked the blood spray
VOIDS