Make all measurements in millimeters
Impact Angle Distance To Point of Convergence (mm) Point of Origin Height (mm) Evidence #1 Evidence #2 Evidence #3
Table 1 – Blood spatter analysis
Rock
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REFERENCE PAGE – TRIGONOMETRY AND BLOOD DROPS – PART 2 *Recall a Right Triangle and its labels:
*A Right Triangle is defined when calculating the Point of Origin from blood spatter.
*This makes it very easy to calculate the Distance To The Point of Origin for blood splatter! Simple use the Trigonometry Formula:
*Tangent works like a conversion factor to convert “degrees of an angle” into units of length so the problem can be worked correctly.
*PROBLEM – What is the Point of Origin of the blood spatter shown below?
Angle A Angle B Angle C side “c” (hypotenuse) side “b” side “a”
Impact Angle (Angle A)
Point of Convergence
Distance from blood drop to Point of Convergence (side “b”) Point of Origin Distance (side “a”) Point of Origin Blood Drop Blood Drops Tangent of Impact Angle (Angle A)
Distance To Point of Origin (side “a”) Distance From Blood Drop To Point of Convergence (side “c”)
=
Distance To Point of Origin 12 inches
Tangent of 70o = Point of Origin?
Impact Angle of Blood Drop #1 = 700
Blood Drop #1 Blood Drop #2
Distance from the front edge of Blood Drop #1 to Point of Convergence = 12 inches Distance To Point of Origin
12 inches 2.75 =
33 inches = Distance To Point of Origin The injury occurred 33 inches above
the Point of Convergence
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QUESTIONS – BLOOD AS EVIDENCE – ANALYZING BLOOD SPATTER
NAME________________________________ 1. A victim was shot and found at the bottom of a ladder. You are preparing to analyze blood spatter at the crime scene to determine if the victim was on the ground or on the ladder when they were shot. What do you need to find first – the Point of Origin or the Point of Convergence?
_________________________________________________
2. You enter a crime scene and discover one, single blood drop. You immediately measure the drop and calculate it’s Impact Angle. However, you will not be able to determine the Point of Origin of this single blood drop. Why can’t you determine the Point of Origin from a single blood drop?
3. Think back to the first Training Lab you completed on blood drops (passive blood drops falling straight down to the ground – not at an angle). How did you determine the Point of Origin Height for these round, passive blood drops?
Use your Figure 1 - “Training Lab Crime Scene” results to answer Questions #4 – #8. 4. List your calculated Point of Origin Heights
in Table 2 (provided to the right). 5. All three of my Point of Origin Height calculations were (check one):
identical similar very different Point of Origin Height (mm) Average Point of Origin Height (mm) Evidence #1 Evidence #2 Evidence #3
Table 2 - Calculated Point of Origin Heights for “Training Lab Crime Scene”
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6. Why should you complete Distance To Point of Origin calculations using several blood drops (like Evidence Blood Drops #1, #2, and #3) rather than simply calculating Distance To Point Of Origin from one drop (like Evidence Blood Drop #1 only)?
7. Calculate your Average Point of Origin Height and record in Table 2.
For Questions #8
**Every 1mm of measurement you make in the miniature crime scene = 1 inch of measurement in the actual room where the crime occurred (scale is 1mm = 1 inch). 8. Remember, blood spatter analysis can help you move back in time to recreate what happened at a crime scene. Let’s give it a try!
About how tall is the victim of the crime? Use a ruler and measure his height. Remember, the scale is 1mm = 1inch.
____________________
What is the Average Point of Origin Height in inches? (scale is 1mm = 1 inch)
____________________
Was the victim most likely: standing / on their knees / on their hands and knees / or lying down near the ground when struck with the rock?
______________________________________________________________ Based on the evidence was the victim likely struck: once / twice / three or more times? ______________________________________________________________
How far did the victim move after being struck before collapsing? (scale is 1mm = 1 inch)
____________________________
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9. Use the blood spatter evidence below to determine how many times the victim was hit (find the Points of Convergence only – you do not need to determine Points of Origin). Also, DRAW A SMALL CIRCLE at each location in the room where the victim was hit.
10.
The victim was hit _________ times.
A victim was shot and you are analyzing the crime scene. You find blood spatter on the wall. You must calculate where along the wall (Point of Convergence), and how far away from the wall (Point of Origin), the victim was standing when they were shot. In this crime scene 1mm = 1 inch, however, the blood drops have been enlarged so they will be easier for you to analyze. PLEASE SHOW YOUR WORK.
A. How far away from the wall (in inches) was the victim standing when he was shot?
The Point of Origin = ________________ B. How far above the ground was the gunshot wound on the victim’s body (in inches)? Simply measure the height._____________ C. What part of the victim’s body was likely shot?__________________________________ HINT - When working with blood spatter on a wall the Point of Origin becomes the distance AWAY FROM THE WALL (not the height). Height can simply be measured
FLOOR
WAL L
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TEACHER NOTES
Lab/Activity:
Training Lab – Blood As Evidence – Analyzing Blood Spatter
Equipment To Prepare:
small millimeter ruler (clear works best)/student
1 scientific calculator OR provided “Table of Sine and Tangent Values”/student or group
Comments/Problems:
This Training Lab usually takes 2 days to complete.
This is a paper and pencil lab activity. Students will be solving simulated crimes by measuring and analyzing simulated blood spatter. This lab requires more Trigonometry, however, students have few problems putting it all together.
Students will obtain the most accurate results if they complete their measurements to the nearest 0.5mm.
Don’t forget to run off the Reference Page – “Trigonometry And Blood Drops – Part 2” for students. This Reference Page will help students understand why they are using
Trigonometry to find the Point of Origin for blood spatter.
Students can use the “Table of Sine and Tangent Values” they received in the previous Training Lab to look up the Tangent values of their Impact Angles (necessary to calculate the Point of Origin) OR students can also use a scientific calculator to find Tangent. You might want to carry around the Key to “Figure 1 – Training Lab Crime Scene” and check student’s work as they are completing it – just to see if they are on the right track. Some students will mistakenly measure the blood drop “tails” when calculating the Impact Angles of Blood Drops “Evidence #1” and “Evidence #3” (they were taught in an earlier Training Lab NOT to measure the “tails”). This will result in an incorrect Impact Angle and incorrect Point of Origin Height.
Students sometimes have a difficult time understanding the concept of Point of Origin. Point of Origin will be HEIGHT above the Point of Convergence when working with blood spatter on the floor. Point of Origin will be DISTANCE AWAY FROM THE WALL when working with blood spatter on a wall. Students will get practice with both floor and wall blood spatter when completing their questions. Make sure students feel comfortable with the concepts of this Training Lab. The upcoming Job will require these exact same skills.
Typical Results:
The Key to “Figure 1 – Training Lab Crime Scene” can be found following these “Teacher Notes”.
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Evidence #2 Evidence #1 Evidence #3 Length = 29mm Width = 7.5mm Length = 27mm Width = 11mm Length = 37mm Width = 8mm 94mm 57mm 108mm
RESULTS WILL VARY SLIGHTLY DEPENDING ON WHERE STUDENTS DRAW POINT OF CONVERGENCE LINES AND HOW THEY MEASURE BLOOD DROPS.
Impact Angle Distance To Point of Convergence (mm) Point of Origin Height (mm) Evidence #1 Evidence #2 Evidence #3 15o 24o 13o 94mm 57mm 108mm 25.2mm 25.4mm 24.9mm