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Bloodstain Pattern Analysis

Bloodstain Pattern Analysis. Bloodstain Patterns. What are they? What do the patterns mean?. Use the size , shape , and distribution of bloodstains to determine how bloodshed happened. Was bleeder standing or on the ground? What type of weapon or object was used?

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Bloodstain Pattern Analysis

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  1. Bloodstain Pattern Analysis

  2. Bloodstain Patterns • What are they? • What do the patterns mean? Use the size, shape, and distributionof bloodstains to determine how bloodshed happened. Was bleeder standing or on the ground? What type of weapon or object was used? Where did bleeding occur and in what order?

  3. Information from Bloodstains • Direction • Angle of Impact • Origin • Applicable Forces • Object Identification • Number of Blood Initiating or Altering Events • Actors Positions • Sequence of Events • Left Handed/Right Handed • Clothed/Unclothed

  4. Analysis of Bloodstain Patterns • Analysis involves an understanding of the physical properties of blood- • High Surface Tension • High Viscosity • Internal Cohesion • Volume Dependent • Reaches Terminal Velocity Gravity Air Resistance

  5. General Characteristics of Blood • Tend to adhere to an external surface. • Spatters when sufficient external forces overcome surface tension. • During free fall drops moves in an oscillating spherical configuration. • The size of a blood drop depends on the size of the surface it fell from. • The longer a distance a drop falls, the larger the diameter of the stain.

  6. Terminal Velocity • Blood falling under the influence of gravity will accelerate like any other falling object. • At some point the force of gravity will equal the frictional force of the air on the droplet. • At this point the drop will no longer accelerate and will reach terminal velocity. • Terminal velocity is dependent on the volume of the drop.

  7. Terminal Velocity

  8. Impact Surface Considerations • Coarse surfaces cause irregularities in patterns. • Blood may break up on impact, and may follow the contour of a surface. • Impact angle and directionality become less reliable as a surface becomes more porous.

  9. Surface Texture Considerations • Nonporous vs. porous • Degree of Stain Absorption • Edge characteristics may be masked

  10. Surface Texture Effects • Harder and NonporousSurfaces (glass or smooth tile) • Less spatter • Rough Surfaces (carpeting or wood) • Irregularly shaped stains with serrated edges and satellite spatter.

  11. “Directionality” • Direction of Travel • Angles of Impact

  12. Direction and Angle of Impact • As the angle of impact deviates from 90° the stain becomes elongated in shape. • The pointedend of a bloodstain faces the direction of travel. • Distorted or disrupted edges of an elongated stain indicates direction.

  13. Direction of Travel • “Tails point to the direct of travel” • What angle?

  14. Angle of Impact a c i b Angle of impact = arcsin i = distance ab/distance bc

  15. Measuring the bloodstains

  16. Changing the Angle of Impact

  17. Confirmation of Sine

  18. Impacted Blood- “More than drops of blood” • Blood source given more force than gravity.

  19. 2D Point of Convergence • Established by drawing straight lines through the long axis of several individual bloodstains. • The intersection or point of convergence of the lines represents the origin point.

  20. 3D Point of Origin “Blood Impacted Here”

  21. Point of Origin of Bloodshed

  22. Impact Bloodstain Spatter • Common Bloodstain that occurs when an object impacts a source of blood. • Forward Spatter – spatter projected outward and away from the source. • Back Spatter – blood projected backward from the source such as an entrance wound.

  23. Classifying Impact Spatter Types • As the force of the impact on the source of blood increases, so does the velocity of the blood drops • Low-Velocity Spatter • Produced by minimal force • Drop diameters of ≥3 mm or more. • Medium Velocity Spatter • Blunt-force trauma • Drop diameters of 1-3 mm • High Velocity Spatter • Gun shot wounds • Drop diameters of ≤ 1 mm

  24. Impacted Blood Types Medium Force High Force

  25. More Bloodstain Spatter Patterns • Gunshot Spatter • Cast-Off Spatter • Arterial Spray Spatter • Expirated Blood Patterns • Void Patterns

  26. Gunshot Spatter • Leaves a pattern of fine drops radiating out in a cone-shaped pattern. • Produces High-Velocity Spatter • May produce both a forward spatter (exit wound) and back spatter (entrance wound)

  27. Cast-Off Spatter • Created when a blood-covered object flings blood in an arc onto a nearby surface. • Occurs when a person pulls a bloody fist or weapon back between blows. • The width of the cast-off pattern may suggest the kind of object that produced the pattern.

  28. “Cast-Off Bloodstains”

  29. Cast-Off Bloodstain Patterns

  30. Arterial Spray Spatter • Occurs when a victim suffers an injury to a main artery or the heart. • Produces a pattern of large spurted stains each time the heart pumps. • The lineup of the stains shows the victim’s movement. • Vertical arcs or waves show fluctuations in blood pressure.

  31. Large Volume of Blood with Force- “Arterial Gushes”

  32. Expirated Blood Patterns • Created by blood expelled from the mouth or nose from an internal injury. • Bubbles of air in the drying drops will be present. • Can be lighter in color due to the dilution with saliva.

  33. Void Patterns • Created when an object blocks the deposition of blood spatter. • The blank space on the surface or object may give a clue as to the size and shape of the missing object or person. • Voids may be used to establish the body position of the victim or assailant.

  34. Other Bloodstain Spatter Patterns • Contact / Transfer Patterns • Flows • Pools • Drip Trail Patterns

  35. Transfer Patterns • When an object with blood on it touches one that does not have blood it produces a transfer pattern. • Simple transfer patterns – when an object makes contact with the surface and is removed without movement. • Swipe pattern – Movement of a bloody object across a surface.

  36. Contact or Transfer Patterns • Bloody object contacting a non-bloody object

  37. Contact or Transfer Patterns • Assume the shape of the original bloody object

  38. Flows • A bloodstain pattern formed by the movement of blood as a result of gravity. • Flow direction may show movements while the flow was still in progress or after the blood has dried. • If a flow does not appear consistent with the direction of gravity, one may surmise the object/body was moved.

  39. Flow Pattern

  40. Pools • Occurs when blood collects in a level and undisturbed place. • An analyst may be able to estimate the drying times of stains of different sizes. • Skeletonization – The edges of a stain dry to the surface. It will remain apparent even after the rest of the blood stain has been disturbed.

  41. Determination of Blood Volume • Use area of a bloodstain to estimate volume of blood present.

  42. Drip Trail Patterns • A series of drops that are formed by blood dripping off an object. • The stains form a line or path usually made by the suspect after injuring or killing the victim. • The shape of the stains can help determine the direction and speed at which a person was moving.

  43. Blood in Horizontal Motion Faster Slow

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