chapter 4 pwpt
TRANSCRIPT
Forensic Science: An Introduction to Scientific & Investigative Techniques
Section 2: The Crime Scene
Section 2: The Crime Scene
Chapter 3: Crime Scene Investigation
Chapter 4: Recognition of Bloodstain Patterns
Chapter 4: Recognition of Bloodstain Patterns
4.1 Bloodstain Pattern Evidence 4.2 History of Bloodstain Pattern Analysis 4.3 Properties of Human Blood 4.4 Formation of Blood 4.5 Altered Bloodstains 4.6 Analysis of Bloodstains on Clothing and Footwear 4.7 Documentation of Bloodstain Evidence 4.8 Absence of Evidence Is Not Evidence of Absence 4.9 Training and Education
Bloodstain Pattern Evidence
Forensic tool to assist Used to:
Corroborate statements Apprehend suspects Interrogate suspects Reconstruction of scene
Strengths and weaknesses Only as valid as
information available and examiners abilities
History of Bloodstain Pattern Analysis
1895 Dr. Eduard Piotrowski
1939 Dr. Victor Balthazard
1955 Dr. Paul Kirk
1971-73 Herbert Leon MacDonell
2002 SWGSTAIN
Properties of Human Blood Biological Properties:
To tissues – Oxygen, electrolytes, nourishment, hormones, vitamins, antibodies
From tissues – Waste products
Plasma → Red and White blood cells and platelets Clotted plasma = serum Nuclei of WBC = DNA
Healthy adults contain 4.5 – 6.0 liters
Physical Properties of Blood Held together by molecular
forces Surface tension = Force
Slightly less than water
To create spatter surface tension must be overcome by an external force
Shape of drop in air is dependent upon the molecular forces acting upon its surface
Physical Properties of Blood
Physical properties allow stability. Viscosity = Resistance
More viscous = moving more slowly
Specific Gravity = weight compared to H2O
Terminal VelocityForce down = force up
Formation of Bloodstains and Bloodstain Patterns – Target Considerations
Big Small Unless disruption of
surface tension
Target texture Smooth – no spatter Rough – spatter
Size, Shape, and Directionality
Directionality Direction of travel Determined through
geometry of stain
Edge Characteristics Narrow end = direction
of travel
Size, Shape, and Directionality
Area of Origin Location of blood source
2D: Long Axes Draw straight lines through
long axes where they converge is the relative source location
3D: Impact Angles Est. angles and project
trajectories back to common axis, 90o from the 2D area of convergence
Size, Shape, and Directionality
Angle of Impact Ratio: Width ÷ Length
Circular →Ratio = 1 → impact 90o
Elliptical → Ratio >1 → impact >90o
Example: Width = ½ Length Ratio = 0.5 Sin-1(0.5) = 30o
Spattered Blood
Identify stain as spatter before determining mechanism
Determining mechanism usually requires more information
Factors Quantity Force Texture
Random distribution of bloodstains created when sufficient force is available to overcome surface tension of blood
Impact Spatter Associated with Gunshot
Mist-like dispersions Wide size range
Factors: available blood, caliber, location, number of shots, and impeding factors
Similar patterns produced by power tools, explosions, machinery injuries, automobile collisions
Impact Spatter Associated with Beating and Stabbing
Size: 1 to 3 mm in diameter
Exposed blood must be present
Number of blows inflicted have effects on the resulting pattern
Significance of Satellite Spatters Resulting from Dripped Blood
Size: 0.1 to 2.0 mm in diameter
Factors: volume, freshness, surface, and distance
Mechanism of spatter causing these stains should be thoroughly explored
Satellite spatter - Smaller droplets of blood that have detached from the main blood volume at the moment of impact
Castoff Bloodstain Patterns
Size: varies greatly Appear linear in
distribution Seen in conjunction with
impact spatters NOT possible to
determine with certainty the object used
Castoff patterns - created with subsequent blows to the same general area where a wound has occurred and blood has accumulated
Bloodstain Patterns Resulting from Large Volumes: Splashed and Projected Blood
Splashed - excess of 1.0 mL subjected to minor force
Ricochet – secondary blood splashing
Projected - blood is projected or released as the result of force
Expirated Bloodstain Patterns
Similar to those of impact spatter from beatings or gunshots
Specific features: Vacuoles – ruptured
air bubbles Dilution from saliva or
nasal secretions
Expirated bloodstain pattern – forcefully expelled blood from the nose or mouth that has accumulated in the lungs, sinuses, and airway passages of the victim as a result of trauma
Arterial Bloodstain Patterns
Size: varies from large gushing to small spray
Factors: severity of injury, size and location, position of victim, and clothing
Very distinctive due to the overall quantity of bloodstains observed.
Transfer Bloodstain Patterns
Experimentation with objects
Chemically enhancing Minute transfer vs.
impact
Transfer pattern – occurs when an object wet with blood comes in contact with an object or secondary surface
Altered Bloodstains
Factors of drying: volume, surface texture, and environmental conditions
Accelerated by increased temperature, low humidity, and increased airflow
Drying visualized from the outside inward
Altered Bloodstains
SKELETONIZED Center of a dried
bloodstain flakes away and leaves a visible outer rim
Central area of a partially dried bloodstain is altered by contact or a wiping motion that leaves the periphery intact
Altered Bloodstains
CLOTTING Initiated when blood
exits the body and is exposed to a foreign surface
Normal clotting time: 3 to 15 minutes
Occurrence of movement after a significant interval of time from the initial bloodshed
Altered Bloodstains
MOISTURESource:
Outside elements Heat, fire, or smoke Cleaning with water or detergents or painted
Moisture dilutes existing bloodstains Use of chemical enhancement to locate
Altered Bloodstains
VOID AREAS Absences of
bloodstains in otherwise continuous patterns of staining
Source: Removal of items
Analysis on Clothing and Footwear
Two questions arise with bloodstained garments: Whose blood is on the garment? DNAHow was the blood deposited onto the
garment? Pattern analysis Passive bloodstaining Active bloodstaining
Analysis on Clothing and Footwear
Steps for Examination: Establish the manner in which the garments were
collected, documented, and preserved prior to their examination.
Document the garments while the victim or suspect is still wearing them, when possible.
Allow the bloodstain analyst an opportunity to examine the stains before their removal for DNA analysis.
Take photographs Obtain a history of garment
Documentation
More than one form of documentationPhotographs, video, diagrams and notes
Size, shape, distribution, overall pattern Measuring devices within the photographs Microphotography Document to allow third party to utilize More is always better!
Absence
Not uncommon for an assailant to have little if any blood on themselves
Absence should neither exonerate nor implicate involvement
Possible explanations: Protective outerwear Removed clothing Directionality away from the assailant
Training and Education
Wide range of backgrounds Required 40 hour course
Key is hands on laboratory experiments
Memberships IABPA
Est. 1983 with ~800 Members Journal of Bloodstain Pattern Analysis
THIS INSTRUCTIONAL UNIT IS NOT A BLOODSTAIN PATTERN COURSE