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Bloodstains

Bloodstains. A field of forensic investigation that deals with: physical properties of blood patterns produced by forces being applied to blood Blood, as a fluid, follows the laws of physics . A blood droplet will remain spherical until it collides with a surface.

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Bloodstains

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  1. Bloodstains • A field of forensic investigation that deals with: • physical properties of blood • patterns produced by forces being applied to blood • Blood, as a fluid, follows the laws of physics. • A blood droplet will remain spherical until it collides with a surface

  2. What can bloodstains tell us? • The distance between the target surface and the origin of blood. • The point of origin of the blood. • Movement of a person or an object. • The number of blows, 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.

  3. Let’s take a closer look……

  4. Conditions Affecting Shape of Blood Droplet • Size of the droplet • Angle of impact • Velocity • 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:

  5. Shape of a Blood Drop • Round—if it falls straight down at a 90 degree angle. • Elliptical—blood droplets elongate as the angle decreases from 90 to 0 degrees.

  6. Bloodstains Exist in 3 forms: Passive; Impact; Transfer • Passive: when natural gravitational forces act on blood. • Can be in the form of: flows, pools, or drips. Ex.Nosebleed

  7. Bloodstains Cont. • Impact: when external forces, other than gravity, act on blood. • Can be in the form of: arterial spurts, castoff, and spatter. • Arterial Spurts • Also known as gushing • Blood exiting the body under pressure from a breached artery

  8. Arterial spurt

  9. Bloodstains Cont. Impact: Castoff • Castoff • Created when a volume of blood is flung from an object. Ex. A bloody object (like a hammer) being swung or coming to a sudden stop. • Stain starts out circular but becomes more elliptical at the end.

  10. Cast Off

  11. Bloodstains Cont. • Backspatter • Blood is acted upon by an outside force and broken into smaller stains. Low Velocity: Size is 4-6 mm in diameter • Occurs with a blunt object impact Medium Velocity: Size is 1-4 mm in diameter. • Generally seen in a beating or stabbing High Velocity: Size is < 1mm in diameter. Produces atomized mist (like hairspray). • Typical of gunshot wound

  12. Impact: Spatter (med velocity)

  13. Impact: Spatter (high velocity)

  14. Bloodstains Cont. • Transfer: when an object comes into contact with blood and transfers a patterned image in that blood onto another surface. Can be in the form of: • Contact • Bloody object comes in contact with a clean surface. • Wipes • Blood is on a surface (and beginning to dry) and is wiped or smeared. • Swipes • Blood is transferred from a moving source onto an unstained surface

  15. Transfer: Contact

  16. Transfer: Wipe

  17. Transfer: Swipe

  18. Bloodstain Pattern Analysis Measuring the Angle of Impact: • The more acute the angle of impact, the more elongated the stain and the easier it is to determine the direction of travel. • 90 degree angles are perfectly round drops • Acute degree angles (Ex. 30 degrees) have an elliptical shape and will begin to produce a tail/spine.

  19. 900 angle 300 angle Tail/Spine

  20. Stain tails point in the direction that the blood drop was traveling.

  21. W L Determining Angle of Impact • Identify the bloodstains you will use. • Measure the width and length of each stain. • Apply the following formula: width = sine of angle impact length inverse sine (arcsine) = Angle of Impact (in degrees)

  22. W L Determining Angle of Impact • The greater the difference between the width and length, the sharper the angle of impact. Ex. Imagine a bloodstain 2 mm wide and 4 mm long. • The width divided by the length is 0.5 • The arcsine of 0.5 is 30 • So the blood hit the surface at a 300 angle.

  23. Based on trig functions of right triangle • Angle of Impact will always be 90o or less. Determining Angle of Impact SIN = Opposite / Hypotenuse COS = Adjacent / Hypotenuse TAN = Opposite / Adjacent

  24. Area of Convergence • The area of convergence is the point of origin - the spot where the “blow” occurred. • The location of the blood source can be determined by drawing lines from the various blood droplets to the area where they intersect. ** Area of Convergence will NEVER come together at a single point.

  25. Point of Origin Determining Point of Origin Distance Area of Convergence Impact Site Tan of Angle of Impact x Distance to Convergence = Distance From Surface

  26. 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. • How will the shape change as the height is increased or decreased?

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