Bloodstain Pattern Analysis

1. Bloodstain Pattern Analysis

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

4. 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

5. What can we learn about blood stains at a crime scene? • The velocity of the blood • The direction of the blood – swing cast off • If the victim was standing, sitting, or laying when beaten or shot • If the victim received the mortal injury where he was found • If the assailant is left or right handed • If there was more than one assailant

6. What can we learn about blood stains at a crime scene? • If the assailant was also wounded • The sequence of wound inflicted • The direction the victim moved after an artery was breached • If the assault occurred before or after the victim was dressed • If the fatal action was a homicide, accident, or suicide

7. To be a spatter pattern, there must be 3 things: • Force – breaks blood source • Flight path • Appearance – at least 3 measurable stains

8. Blood spatter has 3 groups • Impact – needs force • Castoff – no force • Arterial – need force (sharp force trauma) Impact spatters: force + mass + blood source = blood spatter

9. IMPORTANT! • Be able to show any origin of force if you have an impact spatter. • Be able to show any movement through the scene. • What was the weapon used? Tie it to the suspect!