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

What are the biological properties of

blood?

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

Are all blood drops the

same size?

Why?

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

What is the difference between forward and back

spatter?

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

Is the absence of evidence, evidence of

absence?

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

Chapter 4 Summary

Found at most violent crime scenes

Found, documented, analyzed, and interpreted

Scientific analysis = invaluableDates back to 1800’s