Analyzing Blood Evidence

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