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Bloodstain Pattern Analysis Guided Notes

Bloodstain Pattern Analysis Guided Notes. IRP 4 Forensics Mrs. Toth. BPA. Blood spatter examination is termed bloodstain pattern analysis (BPA)

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Bloodstain Pattern Analysis Guided Notes

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  1. Bloodstain Pattern Analysis Guided Notes IRP 4 Forensics Mrs. Toth

  2. BPA • 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

  3. Basic Blood Facts • 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”

  4. 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) • Large, slow drops relate to low-impact injuries (punches) while mid-speed droplets usually relate to a knife or blunt objects • The longer the droplet, the lower the angle of impact

  5. What do blood stains tell us? • 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)

  6. Blood Stains continued… • 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)

  7. What is blood spatter? • 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

  8. Forward vs. Backward Spatter

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

  10. 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)

  11. Wipe stain - created when an object moves through a preexisting bloodstain - Ex. Clean rag through a blood pool 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…

  12. Stains continued… • 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

  13. Stains continued… • 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

  14. 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 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…

  15. 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 • Satellite droplets - small amounts of blood that detach from “parent stains” and splash onto a surface

  16. Basic Measurements of BPA A = arc sin (width/length) • 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

  17. Determining Point of Origin • 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

  18. Documenting Blood Spatter • Size • Shape • Distribution of stains • Viscosity - blood is 3.6 to 5.4x more viscous than water

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

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