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Analyzing Blood Evidence

Analyzing Blood Evidence. Biological Evidence Unit Notes #2. Visual observations: fresh or dried blood should look like blood. If blood has been cleaned up, traces may still be present Luminol will make blood visible under UV light Luminol can contaminate any blood still present

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Analyzing Blood Evidence

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  1. Analyzing Blood Evidence Biological Evidence Unit Notes #2

  2. Visual observations: fresh or dried blood should look like blood. • If blood has been cleaned up, traces may still be present • Luminol will make blood visible under UV light • Luminol can contaminate any blood still present • Cleaned traces can identify a crime scene, but cannot be tested as blood evidence Finding Blood Evidence

  3. Document the location of each piece of blood evidence. • Distance from the victim • Large pool or isolated drips • Collect and package each piece of blood evidence separately to prevent contamination. • Dried blood can be cut out, scraped, or lifted with tape (like a fingerprint). • Wet blood can be collected on the original object (if small) or soaked into a sterile cotton pad. • Allow wet blood to dry as soon as possible. Collecting Blood Evidence

  4. Blood type • Extraction of DNA • Blood location • Drips away from victim could be from the attacker • Blood trails • Blood spatter Analyzing Blood Evidence

  5. When blood drips or splashes onto a wall or floor, the drops can tell us about where the blood came from Blood Spatter

  6. If a drop hits the floor at 90° (straight down), it will form a perfect circle • If a drop hits the floor at an angle, the circle will stretch out Angle of Drops

  7. To calculate the angle that the drop came from: • Measure the width and length of the drop • Divide: width/length • Take the inverse sine (sin-1) of the answer • Your final answer should be between 0-180° Width: 2 cm Length: 5 cm 2 cm/5 cm = 0.4 Sin-1(0.4) = 24° Angle of Drops

  8. Length: • Width: • Width/Length: • Sin-1(width/length): Practice

  9. Stab wounds produce large drops, spread out in clumps • Gunshot wounds produce a fine mist, spread out evenly Type of Weapon

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