Blood spatter 1939spatter patterns first analyzed Blood may spatter when a wound is inflicted Blood spatter patterna grouping of blood stains Patterns help to reconstruct the events surrounding a shooting stabbing or beating ID: 408137
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Blood SpatterSlide2
Blood spatter
1939—spatter
patterns first
analyzedBlood may spatter when a wound is inflictedBlood spatter pattern—a grouping of blood stainsPatterns help to reconstruct the events surrounding a shooting, stabbing, or beating
Forensic Science: Fundamentals & Investigations, Chapter 8
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Blood spatter Analysis
Analysis of a spatter pattern can aid in determining the:
direction blood traveled
angle of impactpoint of origin of the bloodvelocity of the blood
manner of death
Forensic Science: Fundamentals & Investigations, Chapter 8 3Slide4
Blood spatter Analysis
Natural cohesiveness of blood
Forensic Science: Fundamentals & Investigations, Chapter 8
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How Surface texture affects SpatterSlide6
Blood spatter Analysis
Satellite droplets
—
When blood falls from a height, or at a high velocity,It overcomes its natural cohesiveness, and Separates from the main dropletSpiking patterns—Form around the droplet
edges when blood falls onto a less-than-smooth surface
Forensic Science: Fundamentals & Investigations, Chapter 8
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Blood spatter Analysis
—Directionality
The shape of an individual drop of blood provides clues to the direction from where the blood originated.
How will the point of impact compare with the rest of a blood pattern?
Forensic Science: Fundamentals & Investigations, Chapter 8
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Calculating angle of impact
Mathematically, the angle of impact can be calculated by the equation and determining the inverse of Sine A:
Width of blood stain Sin A = -----------------------------
Length of blood stain Slide12
Classifying Impact Spatter
The droplet size can be used to determine the speed in which the impact occurred
Provides insight to crime but not specific eventsSlide13
Impact Velocity vs. size of droplet
Low Velocity Spatter:
Drops with diameters of 4 mm or more normally produced by an applied force of up to 5
ft/sec.Medium Velocity Spatter:Drops with diameters from 1-4 mm with an applied force of 5 to 25 ft/secHigh Velocity Spatter:Drops with diameters of less than 1 mm from an applied force of 100
ft/sec or faster. Slide14
Blood spatter Analysis
—Six Patterns
Describe each of these:
Passive drops Arterial gushes
Splashes Smears Trails Pools
Forensic Science: Fundamentals & Investigations, Chapter 8
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Impact spatterSlide16
Blood spatter Analysis
—Impact
Patterns can help investigators determine the type of weapon used
What kind of a pattern is produced by a gun shot? What kind of a pattern is produced by a hammer blow?
Forensic Science: Fundamentals & Investigations, Chapter 8
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Cast-off spatterSlide18
Arterial spurt spatterSlide19Slide20
Expirated blood patterns
An
expirated blood pattern is created by blood that is expelled from the mouth or nose from an internal injury.
The presence of bubbles of oxygen in the drying drops or a lighter color as a result of dilution by saliva can differentiate a pattern created by expirated blood.The presence of expirated blood gives an important clue as to the injuries suffered and the events that took place at a crime scene.Slide21
Blood spatter Analysis
Forensic Science: Fundamentals & Investigations, Chapter 8
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Lines of convergence
—two or blood
spatters
can pinpoint the location of the blood sourceSlide22
Gunshot spatter
Gunshot spatter is fine forward spatter from an exit wound and back spatter from an entrance wound. However, the gunshot produces only back spatter if the bullet does not exit the body. Slide23
Void patterns
A void is created when an object blocks the deposition of blood spatter onto a target surface or object and the spatter is deposited onto the object or person instead. Slide24
Transfer patterns
A contact or transfer pattern is created when an object with blood on it touches one that does not have blood on it.Slide25Slide26
Skeletonization
The phenomenon of
skeletonization occurs when the edges of a stain dry to the surface.
This usually occurs within 50 seconds of deposition of droplets, and longer for larger volumes of blood.Slide27
Documenting
Investigators should note, study, and photograph each pattern and drop to accurately record the location of specific patterns and to distinguish the stains from which laboratory samples were taken
.
When photographing be sure to include a scale.Slide28
Techniques of Documentation
Two techniques used to document bloodstain patterns are:
Grid methodA grid of squares of known dimensions are set up over the entire pattern.
Perimeter ruler methodA rectangular border of rulers is set up around each pattern and a smaller ruler next to each stain. Slide29Slide30Slide31
Crime Scene Investigation
of Blood
Search for blood evidence
Determine
Is the evidence blood?Is the blood human?What is the blood type?Interpret the findings: Does the blood type match a suspect’s blood?If not, exclude that suspectIf yes, decide if DNA profiling is necessary
Forensic Science: Fundamentals & Investigations, Chapter 8
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