Blood Splatter Identification
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Why is impact splatter important?
○ Indicated a force has been applied to liquid blood ○ Indicated direction and can be used to reconstruct scene
What are blood droplets influenced by?
○ The forces of gravity and air resistance
What are the types of Scene reconstruction methods?
○ Stringing method (manual) i. Uses impact angles and direction of flight to determine the region of origin ○ Tangent method (mathematical) ○ Computer Aided technology
How are blood stains Documented at a crime scene?
○ Photographs, documenting the entire scene ○ When reconstructing point-of-origin, document individual stains used in the reconstruction
What is the difference between a wipe stain and a swipe stain?
The difference is based on the initial location of the blood prior to the contact between the two surfaces. ○Wipe: When an object moves through a pre existing bloodstain. ○Swipe: Transfer of blood onto a target by a moving object that is itself bloodstained.
What is BPA and what can it tell us?
Examines the Blood Pattern Analysis of bloodstains and blood stain patterns: Size Shape Distribution Location Provides information on the event or sequence of events (HOW-activity evidence) that resulted in the deposition of these bloodstains or bloodstain patterns
What kind of science is used in bloodstain pattern analysis?
Physics Maths Biology Anatomy Ballistics Fluid Dynamic
What is serology?
The study of bodily fluids left at crime scenes
What is a presumptive test?
• A Test for blood presence • A highly sensitive that but NOT SPECIFIC for a specific substance • Can identify blood but not if it is human blood or non-human • Instant results • Most of theses tests are based on oxidation-reduction reaction that reacts to the haemoglobin in blood.
Describe the process of a presumptive test
(Screening) The testing chemical is first added, followed by an oxidant (such as 3% Hydrogen peroxide) Types of chemicals used include Phenolphthalein, benzidine, Leucomalachite green and tetramethylbenzidine
What chemicals are used to find the blood pattern or distribution of blood in large areas?
Enhancements such as luminol and amido black
What is a confirmatory test?
Tests for the substance in question and only the specific substance Utilises the formation of crystals through the application of heat and testing chemicals.
What kind of blood enhancements are available?
Luminol Hemascein (fluorescein based test) Amido Black Leuco Malachite Green
What colour clothing can you see blood on using Near Infrared Detection?
Black clothes
What are the compositions and properties of blood?
Composed of Red blood cells and white blood cells
What is plasma?
It is the matrix found in blood Contains 90% water
How is blood used for DNA?
The red blood cells do not contain a nucleus. Whereas the white blood cell has a nucleus, making it possible to extract DNA from
How much blood loss leads to death?
40%, around 2 litres of blood loss
How is blood tested?
Using presumptive (screening) and confirmatory tests Screening Test: TMB (The Hemastix Test) & Kastle Meyer Test Confirmatory Test: Immunochromatographic assays The ABACard Hema-Trace® Test (Abacus Diagnostics)
What are the behaviours of blood outside the body?
Repeatable and predictable
What are the sequences of blood droplet formation?
Sheet > Lattice> Ligaments> Beading> Droplets
What causes the blood droplet formation to form?
Bloods passively onto the surface. Explain how surface tension creates spherical blood drops. The formation of the sphere is a result of surface tension and cohesion that binds the molecules together.
What are the Sequences of Droplet to BLOODSTAIN transition?
Contact/Collapse Displacement/ Spreading Dispersion/Relaxation Retraction/ Equilibrium Wetting
What are the 4 main Categories of bloodstains?
• Passive- by gravity- blood pools • Splatter-w force-create impact pattern • Transfer- fr contact: Compression & Lateral Movt = swipe & wipe. • Altered- changed= diluted or diffused.