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Trigonometry in Blood Spatter
Transcript of Trigonometry in Blood Spatter
-determine the point of origin for a blood spot
-determine the weapon
-determine the extent of the attack
-determine the height and dominant hand of a criminal
Trigonometry in Blood Spatter Analysis
By: Brittany Dorsett
The point of origin of a blood spatter
1. Determine the direction of blood flow in the drops that follow with an arrow next to the droplet.
a. If the blood drop is circular, then the blood fell at a 90 degree angle.
b. If it is not circular, then the angle of impact was less than 90 degree.
c. The elongated end of a drop of blood points to the direction in which the blood was moving
From several drops of blood, determine the area of convergence by drawing lines through each of the blood droplets and noting where the lines intersect
Once you have determined the area of convergence, you will measure the distance from the area of convergence to the edge of the drop of blood when it first impacted a surface.
Next determine the angle of impact for each droplet of blood.
a. Select one of the blood droplets and determine the angle of impact for that drop of blood.
b. To calculate the angle of impact, you will need to use the Law of Sines.
c. Remember, when you measure the length of the blood droplet, do not include the thin extension of the leading edge (tail).
Sin of the angle of impact = width of the blood / length of the blood drop
Use right triangle trigonometry to solve for height.
a. Going back to the right triangle and adding the angle of impact, we can determine the height from where the blood originated.
b. The height of the source of blood is the side opposite the angle of impact.
c. To solve for the height (or side opposite the angle of impact), we apply right triangle trigonometry.
Tangent of angle of impact =
opposite / adjacent = height / distance
Height = tangent of angle X distance
Width of spot: 2"
Length of spot: 5"
Angle of Impact: 24 degrees
distance from spot to point of convergence: 115"
Height(excluding box): 51"
Point of origin: 68"