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Bloodstain pattern analysis can assist in:
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corroborating statements,
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apprehending a suspect,
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reconstructing past events,
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exonerate the accused
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Properties of Human Blood
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Blood is a fluid which circulates throughout body and transports oxygen, electrolytes,
nourishment, hormones, vitamins and antibodies to tissues and organs
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Composed of red blood cells (erythrocytes) and white blood cells (leukocytes), plasma and
platelets
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Properties of Human Blood
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Blood is held together by strong cohesive molecular properties
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These properties create surface tension within each drop and on external surfaces
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Surface tension of blood is slightly less than that of water
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Blood does not fall in tear drop configuration
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Properties of Human Blood
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Volume of typical drop of blood = .05 ml, with an average diameter of 4.56 mm
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Blood is six times more viscous than water
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Specific gravity of blood is slightly higher than water
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These properties tend to allow blood to remain stable and resist alteration or disruption
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Properties of Human Blood
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Blood falling through air increases velocity until force of air resistance that opposes the drop
equals downward gravitational pull – at that point, it reaches terminal velocity
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Estimate for maximum terminal velocity for free falling drop of blood was 25.1 ft per second
(McDonell)
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Properties of Human Blood
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Diameter of bloodstain is due to:
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Function of volume of drop
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The surface texture it impacts
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Up to a point, the distance the blood falls.
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Target Surface Considerations
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Blood will not break apart unless an exterior force disrupts it
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Hard smooth surfaces (glass, smooth tile) create little spatter
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Wood or concrete create significant spatter
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Size, Shape and Directionality
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Geometry of bloodstains will generally allow for determination of their flight
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Narrow end of elongated bloodstain usually points in direction of travel
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After directionality has been determined, an area or point of convergence may be established
by drawing straight lines through long axis of bloodstains
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Size, Shape and Directionality
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Points where lines converge represents the relative location of blood source in a two
dimensional x and y axis
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This convergence location is an area, not an exact point
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Area of Origin – location of blood source, can also be determined three dimensionally
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Size, Shape and Directionality
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Impact angles are done by projecting their trajectories back to a common axis
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If angle of impact is 90 degrees, bloodstain is generally circular
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Impact angles of less than 90 degrees generally result in elliptical bloodstains
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Size, Shape and Directionality
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Width and length of elliptical bloodstain allows for calculation of angle of impact of original
blood drop
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Width is divided by length to produce a ratio number
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Ratio is sine of impact angle: angle can be determined using a scientific calculator or sine
function in trigonometric table
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Example of measurements
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Circular bloodstain: w =1.0, l =1.0 = ratio of 1, which corresponds to impact angle of 90 degrees
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Elliptical bloodstain: w = 1.0, l = 2.0 = ratio of .50, corresponds to impact angle of 30 degrees
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Spattered Blood
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Defined as a random distribution of bloodstains that vary in size and that may be produced by a
variety of mechanisms
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Quantity of available blood can influence spatter
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Amount of force applied also influences spatter
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Spatter is created when sufficient force is available to overcome surface tension of blood
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Spattered Blood
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Spattered blood is significant because:
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Allows for determination of an area or location of the origin of blood source
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If found on suspect’s clothing, may place person at scene of violent altercation
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May allow the determination of the mechanism that created the pattern
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Classification of Blood Spatter
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LVIS - Low-velocity impact spatter – force of up to 5 ft/sec and stains are 4mm in diameter or
greater
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MVIS – Medium-velocity impact spatter- force with velocity of 5-25 ft/sec. diameters of spatter
1- 3mm generally
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HVIS – High-Velocity Impact Spatter – force with velocity above 100ft/sec. diameters are
predominantly smaller than 1 mm
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Classification of Blood Spatter
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Some analysts have discontinued prior terminology and focus on a more conservative approach:
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Identifying spatter created by an impact mechanism
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Identifying spatter created by a projection mechanism
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Spatters are dependent upon quantity of blood, force of impact and texture of surface impacted
by blood
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Impact Spatter Associated with Gunshot
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Mistlike dispersions (less than .1 mm) are associated with spatter associated with gunshot
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May also be a wide size range from .1 mm up to several millimeters or more
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Size range is dependent on quantity of available blood, caliber of weapon, location and number
of shots, and impeding factors, such as hair, clothes.
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Impact Spatter Associated with Gunshot
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Back spatter or blowback- associated with entrance wound and may be found on shooter or
weapon, especially hand and arm area
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Forward spatter – associated with an exit wound
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Impact Spatter Associated with Beating and Stabbing
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Generally exhibits a size range from 1 to 3 mm
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Depends on force of impact and quantity of available blood
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First blow rarely produces spatter- Exposed blood must receive impact
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Type of weapon and number of blows have effects on patterns
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Satellite or secondary spatter: single drops of blood producing small spatters around parent
stain as a result of striking a rough target surface – circular and oval, .1 to 1 mm
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Drip patterns: multiple free-falling drops of blood produced from a stationary source onto a
horizontal surface
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Dripped Blood
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Factors affecting this are:
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blood drop volume
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freshness of blood
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surface texture
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distance of vertical target from impact site
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Castoff Bloodstain Patterns
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Patterns are created by subsequent blows to the same general area where a wound has
occurred and blood has accumulated
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Blood adheres to object producing injuries
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Centrifugal force generated by swinging of weapon is great enough to overcome adhesive force
of blood, thus creating a castoff bloodstain pattern
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Splashed and Projected Blood
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Splashed bloodstain pattern- when quantity of blood in excess if 1.0 ml subjected to low velocity
forces, or allowed to freely fall to surface.
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Secondary ricocheting may occur as a result of deflection
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Expirated Bloodstain patterns
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Expirated bloodstain patterns- blood which accumulates in lungs, sinuses and airway passages
forcefully expelled
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May appear diluted if mixed with saliva or nasal secretions
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Air bubbles or vacuoles are not always present in this type of pattern
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Arterial Bloodstain Patterns
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Arterial bloodstain patterns are caused by breaching of artery and subsequent gushing or
spurting.
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Pattern depends on:
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Severity of injury to artery
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Size and location of artery
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Whether injury is covered by clothing
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Position of victim at time of injury
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Usually large quantity of bloodstains
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Other Bloodstain Patterns
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Blood transfer pattern occurs when an object wet with blood comes into contact with an
unstained object
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Altered bloodstains – are subject to change due to quantity of blood present, and temperature,
humidity and air currents
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Other Bloodstain Patterns
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Skeletonized bloodstain - occurs when central area of a partially dried bloodstain is altered by
contact or wiping motion
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Dried bloodstains age and go through color changes- red to reddish brown to black
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Clotting time assists in measuring amount of elapsed time since injury
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Other Bloodstain Patterns
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Clotted impact spatters may indicate additional activity, such as movement or further injury,
occurred after initial bloodshed
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Evidence of coughing or exhaled blood may be associated with post injury survival time
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Bloodstains can be altered by wiping, smudging, wiping, or effects of moisture
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Other Bloodstain Patterns
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Suspected cleaned areas of bloodstains may be visualized with luminol
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Heat, fire or smoke may also alter bloodstain patterns
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Heat and fire can destroy bloodstain patterns
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Interpretations of Bloodstains on Clothing and Footwear
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Two questions arise with bloodstained garments:
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Whose blood is on garment?
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How was blood deposited on garment?
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DNA technology has assisted in identification of whose blood is present
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Interpretations of Bloodstains on Clothing and Footwear
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Two categories of bloodstain deposition onto garments
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Passive bloodstaining – transfer, flow patterns, saturation stains, and stains from
dripping blood
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Active bloodstaining – impact spatter, arterial spurts, expirated bloodstains, and castoff.
Interpretations of Bloodstains on Clothing and Footwear
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Bloodstain patterns must be identified and documented
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Serological findings should be reviewed before drawing conclusions
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Interpretation of bloodstain patterns centers on substantiating or refuting suspect’s version of
events
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Interpretations of Bloodstains on Clothing and Footwear
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To facilitate examination of clothing by bloodstain analyst:
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Establish manner garments were collected, documented and preserved
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Document garments while victim or suspect is still wearing them
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Allow bloodstain pattern analyst to examine garments before removal for DNA analysis
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Interpretations of Bloodstains on Clothing and Footwear
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Take photomacrographs and photomicrographs of before cuttings or stains are removed
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Obtain a history of garment handling and where it has been – check for contamination or
compromise of garment
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Documentation of Bloodstain Evidence
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Degree of significance of bloodstain pattern analysis can be enhanced by:
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Accurately documenting size, shape and distribution of the individual stains and
patterns
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Including measuring devices within photographs
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Using more than one mechanism for documentation; photographs, video, diagrams,
and notes
Documentation of Bloodstain Evidence
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Collect articles of evidence that may contain significant or questionable bloodstain
patterns, if possible
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Utilize overall, mid-range and close-up macrophotography when documenting
bloodstain patterns – overlap photographs
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Documentation of Bloodstain Evidence
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Complete documentation in a manner which allows 3rd party to utilize the photographs,
notes, diagrams, and video to place eh bloodstain patterns and articles of evidence back
in their original location
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Remember, you can never take enough photographs
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The Use of Luminol Photography for Bloodstain Pattern Analysis
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Luminol is a chemiluminescent reagent that can be utilized both as a presumptive test for blood
as well as a method of chemical enhancement of impressions in blood on various surfaces
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Used to check for latent prints or bloodstains where area has been cleaned by suspect or others
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The Use of Luminol Photography for Bloodstain Pattern Analysis
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Luminol is not specific for human blood- also reacts with animal blood
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Should be used in darker conditions
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Special photography should be used – 35 mm camera with a wide open aperture – f-2.8 or f-3.5
with an exposure time of 40 to 80 seconds
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Color film is preferred
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Photograph before and after application
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Absence of Evidence Is Not Evidence of Absence
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Absence of bloodstaining on an active participant can be explained by:
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Directionality of blows may direct spatters away from assailant
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Site of injury covered with clothing reduces spatter
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Assailant may clean up or change prior to being apprehended
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Assailant may have worn protective outerwear
Absence of Evidence Is Not Evidence of Absence
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The assailant may have removed his clothing prior to assault
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Amount of blood present (bloodbath) may be due to active bleeding from victim who is
still alive or draining of blood from wounds of a deceased victim
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Individuals have been known to confess to crimes they did not commit
Report Writing
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Purpose of bloodstain pattern report is to convey findings of analyst to attorneys, court, and
jury
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Report should include all overall observations and experiments from which final conclusions are
rendered
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Report Writing
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Report should contain introduction, body and conclusions.
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Report Writing
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Introduction - name of victim, suspects, case number, location of crime scene, list of
materials and evidence, and who requested analysis
Body of report – crime scene description, physical evidence collected at scene, victim’s
body and autopsy information, victim’s clothing and footwear, suspect’s body, suspect’s
clothing and footwear, reconstruction, chemical enhancement techniques, experiments
Report Writing
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Conclusion – findings should be listed in sequential order, limited to scientific
foundations, fall within bloodstain analysis discipline, and expertise of analyst.
Photographs and diagrams may accompany the report
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Training and Education
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There are a variety of experts from disciplines such as chemistry, biology, and physics
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It is highly recommended individuals enroll in a forty hour basic bloodstain interpretation course
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IABPA- International Association of Bloodstain Pattern Analysts, formed in 1983, is organization
for this field of study.