1. Bell Assignment Monday 10/27
List 5 common types of physical evidence.
In order to identify a substance, what must be done to it?
When comparing a piece of evidence, it must be compared to what 2 things?
Since you can’t calculate the exact probability, what do forensic scientists try to do with the evidence?

2. Blood-Drop Analysis

3. Why Analyze the Drops
Patterns left by falling or projected drops of blood can help determine where a crime took place
Blood drops and stains examined closely before evidence is collected to keep the perspective

4. Shape of Drops Indicates
Distance from which the blood fell
Angle of impact
While droplet is falling, it is primarily spherical in shape. Not tear-shaped like in cartoons
Smaller the drop, the more spherical the shape during fall

6. Drop Acceleration
As a drop falls it accelerates until it reaches a constant or terminal velocity
Measurements have shown that a blood drop, resulting from dripping at a height of 15 ft, has a volume of about 0.05mL and falls at a velocity of ~ 25ft/s.
Smaller drops have a terminal velocity less than 25 ft/s and larger drops are greater than 25 ft/s

7. Drop Acceleration, cont.
Individual blood droplet can give an investigator the following information:
The droplet’s speed at time of impact
Direction droplet travelled
Approximate size of blood drop
What could the droplet’s size tell an investigator about the wound it came from?

8. Round Drops
If you examine a blood droplet that struck a surface straight-on (90-degree angle from the surface), the droplet is generally round
Straight-on impacts on hard, smooth surfaces produce droplets with smooth edges
Higher velocities and rougher surfaces produce drops with more ragged edges

9. Elongated Drops Angle of impact affects the droplet’s shape
Droplets falling on surfaces at an angle that is greater than 90 degrees have elongated shapes.
The larger the angle, the more elliptical the droplet

12. Dripping and Spraying
A droplet that forms slowly, as in a dripping wound, has a volume of about 0.05 mL.
Smaller droplets are produced during active situation – fight or beating
Blood droplets as small as an aerosol spray indicate the wound was produced by a powerful force – gunshot or explosion

13. Bloodstain Pattern Analysis Tutorial
J. Slemko Forensic Consulting