Bloodstain Pattern Analysis Guided Notes IRP 4 Forensics

Bloodstain Pattern Analysis Guided Notes IRP 4 Forensics Mrs. Toth

BPA v v Blood spatter examination is termed bloodstain pattern analysis (BPA) Defined as the analysis and interpretation of the dispersion, shape characteristics, volume, pattern, number, and relationship of bloodstains at a crime scene to reconstruct a process of events

Basic Blood Facts v v Blood has 4 components: 1. RBC 3. WBC 2. Platelets 4. Plasma Blood is under high pressure in arteries and low pressure in veins Blood types include A, B, AB, and O (Landsteiner) Blood contains hemoglobin which is important for chemical testing to identify liquids as “blood”

Basic Blood Facts Continued… The smaller the blood drop, the faster the velocity of it; a fog of tiny droplets indicates high velocity (gunshot or explosive device) v Large, slow drops relate to low-impact injuries (punches) while mid-speed droplets usually relate to a knife or blunt objects v The longer the droplet, the lower the angle of impact v

What do blood stains tell us? v v v Point of origin and the direction of blood travel Type of force and number of blows Sequence of events and the position of the victim and the perpetrator The movement of people/objects Confirm/refute assumptions and witness accounts Blood spatter does NOT tell age, sex, disease, alcohol level, temperature, or humidity (serology does this)

Blood Stains continued… v To determine if a stain is blood, 4 general reagents are used: - phenolphthalein (called Kastle-Meyer test) - leucomalachite green (swab turns greenish/blue) - tetramethylbenzidine (swab turns intense blue color) - luminol (sprayed on; viewed in darkness with UV light)

What is blood spatter? v v Definition: - in blood pattern analysis, it describes a stain that results from blood hitting a target Two types of spatter: 1. Forward spatter: results when blood droplets are projected away from the item creating the impact Ex. Hammer 2. Back spatter: caused by droplets being projected toward the item; generally lighter and stains are smaller

Forward vs. Backward Spatter

Types of Bloodstains 1. 2. 3. Passive: clots, drops, flows, pooling Transfer: wipes, swipes, pattern transfers, general contact stains Projected/Impact: spatters, splashes, castoff stains, arterial spurts or gushes - other stains include fly spots, voids, and skeletonized stains

Bloodstain Types A. Passive Bloodstain B. Impact Bloodstain (medium velocity) C. Cast-off Bloodstain D. Arterial Gush (Spurt) Bloodstain E. Wipe bloodstain F. Transfer bloodstain (knife blade pattern)

Stains continued… v Wipe stain - created when an object moves through a preexisting bloodstain - Ex. Clean rag through a blood pool v Swipe stain - transfer of blood onto a target by a moving object that is itself bloodstained - Ex. Blood-soaked clothing being dragged over unstained vinyl flooring

Stains continued… v Cast-off stains - result of blood being flung or projected from a bloody object in motion or one that stops suddenly - these stains are linear and reflect the position of the person moving the bloody object

Stains continued… v Arterial spurts/gushes - stains that are a result of the pumping action and variable pressure of blood as it exits a wound, producing an up-and-down pattern

Stains continued… v Fly spots - stains resulting from fly activity - flies may regurgitate and defecate when consuming blood at a crime scene - these can be misleading to investigators v Voids - outlined or shadowed bloodstain patterns on a wall or object that was behind the object of impact - indicate some secondary object came between a blood spatter and the final target - important because can tell investigators if items were moved or discarded after the attack

Stains continued… Skeletonized stains - wiped bloodstains where the edges have dried leaving behind edges and borders - these stains retain the size and shape of the original stain and indicate time has passed v Satellite droplets - small amounts of blood that detach from “parent stains” and splash onto a surface v

Basic Measurements of BPA A = arc sin (width/length) v v v Angle of impact: the acute angle created by the intercept of the target with the droplet’s vector Direction angle: angle between the long axis of the stain and a standard reference point, usually 0º vertical Directionality: the vector of a droplet when it hit the target; the tail points in the direction of travel

Determining Point of Origin v v Where lines converge at a common point indicates the possible point of origin Visual aids such as string; rulers, protractors, and lasers help analysts determine lines of convergence

Documenting Blood Spatter v Size v Shape v Distribution of stains v Viscosity - blood is 3. 6 to 5. 4 x more viscous than water

Documenting Blood Spatter continued… v Diameter of blood depends on: - volume - distance of fall - surface texture of what it falls on