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Blood Spatter Evidence

Blood Spatter Evidence. A field of forensic investigation which deals with the physical properties of blood and and the patterns produced under different conditions as a result of various forces being applied to the blood. Blood, as a fluid, follows the laws of physics.

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Blood Spatter Evidence

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  1. Blood Spatter Evidence A field of forensic investigation which deals with the physical properties of blood and and the patterns produced under different conditions as a result of various forces being applied to the blood. Blood, as a fluid, follows the laws of physics.

  2. Blood Droplet Characteristics • A blood droplet will remain spherical in space until it collides with a surface • Once a blood droplet impacts a surface, a bloodstain is formed. • A droplet falling from the same height, hitting the same surface at the same angle, will produce a stain with the same basic shape. • How will the shape change as the height is increased or decreased?

  3. Conditions Affecting Shape of Blood Droplet • Size of the droplet • Angle of impact • Velocity at which the blood droplet left its origin • Height • Texture of the target surface • On clean glass or plastic—droplet will have smooth outside edges • On a rough surface—will produce scalloping on the edges

  4. Blood Pattern Analysis • The use of physics and math to interpret bloodstain patterns within a forensic setting • May show: • Activity at scene • Number of blows • Position of victim and assailant • Whether death was immediate or delayed • Weapon characteristics

  5. Blood Spatter Effect of Surface • Smooth surface = smooth sphere • Rough/porous surface may cause some splatter

  6. Bloodstain Terminology • Spines • Satellite Spatter

  7. Questions Answered by Blood Spatter Interpretation • The distance between the target surface and the origin of blood • The point(s) of origin of the blood • Movement and direction of a person or an object • The number of blows, shots, etc. causing the bloodshed and/or the dispersal of blood. • Type and direction of impact that produced the bloodshed • The position of the victim and/or object during bloodshed • Movement of the victim and/or object after bloodshed

  8. Blood Evidence • Class evidence for blood would include blood type. If you can determine the DNA you would have individual evidence. • Blood stain patterns are considered circumstantial evidence in a court room. Experts could argue many points including direction of travel, height of the perpetrator, position of the victim, left/right hand, whether the body was moved, etc.

  9. Blood Spatter Spattered Blood • In general, for higher impacts, the pattern is more spread out and the individual stains are smaller. • Low impact = beating • High impact = gunshot

  10. Blood Spatter Types of Spatter • Beating and Stabbing Spatter = larger individual stains • First blow usually doesn’t result in spatter since there is not yet any exposed blood.

  11. Blood Spatter Types of Spatter • Gunshot Spatter = can result in a mist-like spatter that indicates a gunshot. • Not all gunshots will result in misting. • If misting is present, it is most likely a gunshot.

  12. Determining Location of Blood Source • Direction of travel – tail will point in direction of travel • Angle of impact • Vertical drops are circular • Drop elongates as angle increases • Measure width and length then calculate angle it struck the surface • Attach string lines to each of the spatters and lines converge at the blood source

  13. Blood Spatter Determining Direction of Blood • Narrow end of a blood drop will point in the direction of travel.

  14. Image by Kevin Maloney

  15. Area of Intersectionand Convergence The location of the blood source can be determined by drawing lines from the various blood droplets to the point where they intersect. The area of convergence is the point of origin; the spot where the “blow” occurred. It may be established at the scene with measurement of angles by use of strings.

  16. Blood Spatter • For each blood drop, a string can be guided back to the point of origin.

  17. Blood Spatter Determining Direction of Blood • This is a 2-dimensional point of origin. • It is possible to determine the 3-D point of origin

  18. String Convergence in a 2 Dimensional Plane Convergence

  19. Point of Origin Localization

  20. String Method

  21. Other Patterns in Blood • Transfer patterns (gun, knife, hand, foot…) • Void patterns (indicating some object was removed or a person was hit by spatter) • Flow patterns (may indicate movement with change in flow)

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