Bloodstain Pattern Analysis Notes
Bloodstain Pattern Analysis (BPA)
Introduction
Ted Selineks, a retired forensic scientist from the Forensic Science Centre of South Australia, specializing in bloodstain pattern analysis.
BPA involves examining bloodstained clothing and crime scenes to understand events.
The video contains bloodstained images; viewer discretion is advised.
BPA is popularized in television shows like Dexter, where the title character uses it to analyze crime scenes.
Dexter Example
A clip from Dexter illustrates the use of stringing to determine the point of origin of bloodstains.
Dexter uses bloodstain patterns to deduce the sequence of events and identify the shooter.
Definition of BPA
Bloodstain Pattern Analysis: Examination of the size, shape, and distribution of blood stains at a crime scene.
Underpinned by sciences such as physics, maths, and biology.
Information Provided by BPA
Sequence of events at a crime scene.
Location and orientation of individuals during bloodletting.
Movement of people through the crime scene.
Number of blows or shots.
Location of blows or shots on the body or within the scene.
Mechanisms that produced the bloodstains (e.g., impact, cast-off).
Types of injuries sustained (e.g., arterial severance).
Blood Basics
Blood is the most commonly encountered fluid at crime scenes.
Circulates through arteries, veins, and capillaries.
Cohesive properties: Surface tension draws blood into a droplet.
Adhesive properties: Blood adheres to various surfaces.
Blood Composition:
45% red blood cells (erythrocytes): no nucleus, but contain heme molecule targeted for forensic screening.
55% plasma.
White blood cells (leukocytes): contain a nucleus, targeted for DNA analysis.
Platelets: involved in the clotting process.
Blood Volume and Loss:
Average male: 5 liters of circulating blood.
70 ml of blood per heartbeat.
At 150 beats per minute, liters of blood circulate per minute.
Loss of over 40% (2 liters) can be fatal without immediate treatment.
Screening Tests
Sensitive but not specific; quick results.
Based on oxidation-reduction reactions catalyzed by the heme molecule.
May produce a colored precipitate, chemiluminescence (like luminal tests in Dexter), or fluorescence.
Common Tests:
Hemostix Test: A test strip with a chemical pad rubbed against a suspected bloodstain, add a drop of water, and look for a green color reaction.
Reaction time indicates blood dilution.
Castle-Mire Test: Chemicals are added to a blood sample, resulting in a pink coloration.
Requires regular validation and QA, which affects lab usage.
Confirmatory Tests
Navicar Hematrace Test: Uses antibodies to detect human hemoglobin.
Small piece of blood stain extracted with a buffer, then placed at the bottom well of test strip.
Potential for false positives exists.
Blood Enhancements
Used to locate and visualize latent or trace bloodstains.
Chemiluminescent reactions (e.g., luminal).
Hemosene: Requires an alternate light source at nanometers to make blood fluoresce.
Common enhancements: amido black and leuco-malachite green.
Examples:
Luminal: Used in the dark to visualize blood, such as a handprint on black clothing.
Amido Black: Enhances bloodstains on surfaces like wooden floors, revealing footmarks and drag marks.
Leuco-Malachite Green: Documents blood after hand washing to enhance documentation. *Near infrared detection: Useful for black clothing. Blood becomes black and dyes appear lighter.
SLR camera is modified for infrared.
Near Infrared Detection: Used for clothing, operates from to over nanometers. Blood appears black on black clothing due to differential light absorption.
Behavior of Blood
Adheres to the laws of physics; repeatable and predictable.
Blood impacting another droplet results in satellite spatter.
*Impact Spatter: hammer is used on blood to show sheeting, lattice, and droplet formation.Droplet Formation: Due to surface tension, blood forms a sphere and goes through sheeting, crowns and sheets, lattice formation, and satellite spatter.
Impact on Surfaces:
Contact phase, spreading, and retraction due to surface tension.
On angled surfaces, forms an ellipse.
*There are 4 main categories of blood stains which are passive, spatter, transfer, and altered stains.
Categories of Blood Stains
Passive: Gravity is the main force.
Spatter: Force applied to the blood.
Transfer: Direct contact.
Altered: Changed, diluted, or cleaned up.
Passive Blood Stains:
Drip stains, drip patterns, flow patterns, and blood pools.
Example:
Clotted blood with serum around outside.
blood is clotted at crime scene
Spatter Blood Stains:
Created when force acts on an exposed blood source, breaking surface tension.
Force + blood source causes smaller spherical droplets to form.
Impact spatter: Force from an implement or fist impacting a blood source.
Forward spatter: Associated with gunshot wounds.
Back spatter: Comes toward the person who fired the implement.
Cast off: Blood flung off an object (e.g., cardboard tube).
*Arterial Projected Spatter: Is often a wave pattern due to change in pressure as the heart beats.Arterial projected spatter: Results from injury to arteries, creating a wave-like pattern due to heartbeats.
Expiratory spatter: From injuries to airways, blood is coughed up.
Transfer Blood Stains:
Compression transfer: Direct contact.
Lateral transfer: Movement across a body.
Swipes: Bloodstained surface contacts another with movement involved.
*knife folder on a shirt is then wiped through.
Altered Blood Stains:
Diluted bloodstains or diffuse stains from diluted blood.
Clotted bloodstains or insect artifacts (fly feces or regurgitation).
Water can influence how bloodstains form.
Clotted blood spatter indicates an ongoing event.
Impact Spatter and Crime Scene Reconstruction
Directionality indicates the angle of impact which facilitates crime scene reconstruction.
Angle of impact discovered in 1895.
Width vs. length in a sine calculation to find the angle of impact (discovered in 1939).
*If looking at the angle of impact, you must look at the width of it
Angle of Impact Calculation:
Basic trigonometry is applied. The blood is reproducible so its angled and measured.
Factors Influencing Blood Droplet Flight: Gravity and air resistance.
Smaller mass = less distance.
Stringing Method:
Red strings used in the Dexter movie to determine the region of origin.
Tangent method is a mathematical calculation.
Computer-aided technology can pinpoint areas accurately.
Measuring Bloodstains:
Measure the width accurately, leading edge may be distorted so width is used.
Use well formed upward-traveling spatter stains.
Area of Convergence & Region of Origin
Area of Convergence: Draw lines along the long axis to find convergence in two dimensions.
Region of Origin: Add the angle of impact for a three-dimensional point in space.
*tangent method to move the 2d drawing of where the bloodstains from each impact converged into 3D space.
Clothing Examination
Difficult due to absorbent surfaces changing bloodstain shapes of the blood.
Textile science is helpful.
Information Gained:
Position of someone at the time of blood deposition.
Proximity between victim and suspect and indicate injury.
injuries may show that the body was upright for a time.
Curved surfaces can distort angles of impact.
Two-dimensional vs. three-dimensional examination (using a mannequin).
Analysis of bloodstains on jeans, showing flow patterns from a head injury while sitting or lying down.
Drip Stains: Can be simulated in a lab like in the example here to show the actual drip stains on jean
Analysis of hand marks, showing cast-off from the fingertips that indicates force of impact.
Analysis of spatter stains on clothing, using 3D reconstruction to determine the position of the person receiving impacts.
*If fighting with a defector who used a knife the victim must have let out across the person's leg.Pattern analysis of blood spatters due to bat beating to determin if left or right handed.
Conclusion
*Any Questions Please Email Me.