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BLOODSTAIN PATTERNS

BLOODSTAIN PATTERNS. BLOOD COMPONENTS. Plasma fluid portion of normal unclotted blood red blood cells, white blood cells, and platelets are suspended in it. BLOOD COMPONENTS. Serum liquid portion of clotted blood. SURFACE TENSION OF BLOOD.

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BLOODSTAIN PATTERNS

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  1. BLOODSTAIN PATTERNS

  2. BLOOD COMPONENTS Plasma • fluid portion of normal unclotted blood • red blood cells, white blood cells, and platelets are suspended in it

  3. BLOOD COMPONENTS Serum • liquid portion of clotted blood

  4. SURFACE TENSION OF BLOOD • held together by strong cohesive molecular forces • “outer skin” • Surface tension lightly less that that of water • Liquid mercury is about 10x greater • Blood does not fall in teardrop configuration

  5. SURFACE TENSION • To create splatters, an external force must overcome surface tension of blood

  6. SURFACE TENSION Surfaces • Generally, clean glass or smooth tile, very little splatter • Rough texture, wood or concrete, significant splatter

  7. GEOMETRY OF BLOODSTAIN • Can determine direction of flight by examining edge characteristics

  8. GEOMETRY Angle of impact 90 degrees • results in circular shape

  9. GEOMETRY Angle of impact Less than 90 degrees • Elongated

  10. GEOMETRY • If you measure width & length of an elliptical bloodstain you can calculate angle of impact • Divide width by length • take sin-1 • gives angle of impact

  11. Geometry • Once get angle of impact for each bloodstain • 3D origin may be determined

  12. DIRECTION OF TRAVEL • Narrow end of elongated blood stain points in direction of travel

  13. SPATTERED BLOOD • random distribution of bloodstains that vary in size that may be produced buy a variety of mechanisms

  14. SPATTERED BLOOD Examples: • Gunshot • Beating • Stabbing • power tools • Arterial • cast-off • passive

  15. SPATTERED BLOOD • may allow determination of an area • or location of origin of blood source

  16. SPATTERED BLOOD • If found on a suspect’s clothing, it may place that person at scene of violent altercation

  17. SPATTERED BLOOD • May allow determination of mechanism by which pattern was created

  18. SIZE, QUANTITY AND DISTRIBUTION OF SPATTER DEPENDS ON • Quantity of blood subjected to impact • Force of impact • Texture of surface impacted by blood

  19. GUNSHOT • High Velocity Spatter • Misting effect • Varying sizes of impact spatters • Depend of caliber of weapon, location, number of shots, etc.

  20. Gunshot

  21. EXAMPLE BACK SPATTER

  22. EXAMPLE GUNSHOT IMPACT SPATTER

  23. Beating and Stabbing Impact SpatterMedium Velocity Spatter • Generally size range 1-3 mm in diameter

  24. Castoff Bloodstain PatternsLow Velocity Spatter • Blood flung from object – such as bat or knife

  25. Passive BloodstainsLow Velocity • Blood dripping from injured person

  26. What happens when blood hits blood? • Drip patterns

  27. Large Volume Bloodstains • Splashing and ricochet • Often from victim with large wound or vomiting

  28. EXPIRATED BLOODSTAIN PATTERNS • Blood accumulates in lungs, sinuses, airway passages of victim • Forcefully expelled from living victim • Can look similar to other bloodstain patterns • can only be explained if victim has blood on face

  29. ARTERIAL BLOODSTAIN PATTERNS • Can be very large gushing or spurting patterns to very small spray types

  30. OTHER BLOODSTAIN PATTERNS • Transfer bloodstain patterns • Altered bloodstains • Void areas or patterns

  31. INTERPRETATION OF BLOODSTAINS ON CLOTHING AND FOOTWEAR • Whose blood is it? • How did it get there?

  32. LUMINOL • Used for latent bloodstains at crime scene

  33. CHALLENGES • Bloodstain pattern interpretation can be very complex Need solid grasps of: • Mathematics • Physics • scientific method • practical experience

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