Bloody Trig

Being a blood spatter analyst is not all fun and games, it's all crime sciences at every hour of the day and night.

It does help when you have an expert team like I do, my forensics team consists of me, Jocelyn Guzman, Natalie Costa, and Coleman Richard.

We just got called into a crime scene (go figure just when I started my lunch break). The scene was located inside an apartment that belonged to our victim, Jenny Fern. Our witness, Fern's ex fiancé Joshua Miller, found Fern splayed out on her side on the floor. In this crime scene there were two main locations of blood spatter.

The first location was from a 90˚ angle.

And the second location was from a non-90˚ angle.

We know the location because if the blood drop is circular, then the blood fell at a 90˚ angle. If it is not circular, then the angle of impact was less than 90˚ angle. The elongated end of a drop of blood points to the direction in which the blood was moving

Through trigonometry our team is able to identify: the point of origin for a blood spot, the weapon, the extent of the attack, and the height and dominant hand of a criminal.  

90˚ Blood Spatter

Blood analyst Coleman Richard chose 3 different blood spots from the first location, the 90˚ angle blood spatter, and measured the angle of elevation. To calculate the the angle of elevation you need to use the Law of Sines. 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

Spot 1-Width= 2cm Length= 2cm Calculated Angle= 90˚

2cm/2cm = 1cm

Inverse sin of 1cm= 90˚
Spot 2-Width= 4cm Length= 5cm Calculated Angle= 53.13˚

4cm/5cm = .8cm

Inverse sin of .8cm = 53.13˚
Spot 3-Width= 1cm Length= 1cm Calculated Angle= 90˚

2cm/2cm = 1cm

Inverse sin of 1cm= 90˚

Non-90˚ Blood Spatter

This time our other blood analyst, Natalie Costa, chose 3 different spots from the other location, the non-90˚ blood spatter, to calculate the angle of elevation.

Spot 1-Width= 1cmLength=1.5cmCalculated Angle= 41.8˚

1cm/1.5cm= .66cm

Inverse sin of .66cm = 41.8˚

Spot 2-Width= 1.5 cmLength=2.5cmCalculated Angle= 36.9˚

1.5cm/2.5cm= .6cm

Inverse sin of .6cm = 36.9˚

Spot 3-Width= 1.5cmLength= 2cmCalculated Angle= 48.6˚

1.5cm/2cm= .75cm

Inverse sin of .75cm = 48.6˚

The Murder

Through the measurements and calculation, and the help of our forensics team, we were finally able to solve the murder. The murderer was Jenny Fern's ex fiancé, Joshua Miller.


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