TRAINING LAB BLOOD AS EVIDENCE ANALYZING BLOOD SPATTER NAME Background: You have learned how to analyze individual blood drops to determine the height a passive drop fell, the direction a moving drop was falling when it hit a surface, and the Impact Angle of a falling drop. It s now time to learn how to put it all together and interpret the blood spatter at a crime scene to find out where the blood drops came from, to move back in time to recreate what happened and tell the story of the crime. 1. You will be trained to analyze blood spatter pattern to determine the Point of Convergence. 2. You will be trained to analyze blood spatter pattern to determine the Point of Origin. Procedures: Part 1 The Appearance Of Blood Spatter 1. The initial blood spatter from a gunshot wound usually forms a collection of many, smaller blood droplets that fly outward from the wound and may land on walls, ceilings, or floors. 2. The initial blood spatter traveling from someone being hit usually forms average-sized blood drops that fly outward from the wound and may land on walls or floors. 3. Blood spatter from a swinging weapon usually forms a long line of average-sized blood drops that may land on walls, ceiling, or floors. 4. Blood spatter from a bleeding wound usually forms average-sized drops that drop to the ground. They can be round if the person is standing still, or oval-shaped if the person is moving. Part 2 Analyzing Blood Spatter To Determine The Point Of Convergence 1. A blood spatter pattern on the wall, floor, ceiling, or similar surface can help you find the location in a room where a victim was injured. 2. Your first step is to draw STRAIGHT LINES through all the blood drops that fell at an angle to see where they came from (you don t need to draw lines through the perfectly round blood drops you already know they came from a wound directly above the drop). A. Use a ruler/meter stick to draw your straight lines OR stretch out and tape down strings to form the straight lines. B. Draw lines through the Long Axis of the blood drops (see picture at right). C. Draw the line so it travels back toward where the drop came from (opposite the direction of travel). direction of travel 53
3. The collection of lines through several blood drops should intersect at some point. This area of intersection is called the POINT OF CONVERGENCE (see the diagram at the bottom of the page). The Convergence is the location where the injury must have taken place and it is always where your blood drop travel lines intersect. 4. Look at Figure 1 Training Lab Crime Scene. The Setup - This page represents a miniature version of a floor in a room. Everything is drawn to scale, exactly as it was found in the room. However, the blood drops have been enlarged so they will be easier for you to analyze. MAKE ALL MEASUREMENTS IN THIS MINIATURE ROOM USING MILLIMETERS. The Story - A male victim was found unconscious on the floor and had been hit in the head with a rock. Blood spatter evidence is present on the floor (the blood drops have been enlarged for your analysis). No suspects have been located. The Problem You must: 1. Find where the victim was located in the room when he was struck with the rock (the Convergence). 2. Determine the exact height of the victim s head when it was struck with the rock (was the victim standing, kneeling, or lying on the floor?). 5. Determine the Point Of Convergence in the Training Lab Crime Scene by drawing lines though the blood drops and looking for the point of intersection. This intersection point is where the victim was located in the room when he was struck with the rock. 6. To determine the height of the victim s head when it was struck will require a little more work. Move on to Part 3 to learn how to answer this problem. Part 3 Analyzing Blood Spatter To Determine The Point Of Origin 1. The Convergence is important when analyzing blood spatter it shows you the general location where an injury was inflicted at a crime scene. However, EXACTLY where along a line extending out from the Convergence did the injury occur close to the surface or far away from the surface? 2. The EXACT location of where the injury occurred along this Convergence line is called the POINT OF ORIGIN. Convergence IF BLOOD SPATTER IS ON A WALL The Origin How far away from the wall (out from the Convergence) did the injury occur? IF BLOOD SPATTER IS ON THE FLOOR The Origin How high above the floor (above the Convergence) did the injury occur? Convergence 54
THE POINT OF ORIGIN CAN BE EASILY CALCULATED 3. To calculate the Origin complete the following steps. Step #1 Determine the Convergence Step #2 Calculate the Impact Angle of one of the blood drops you used to find the Convergence (DO NOT measure tails!). Step #3 Accurately measure the distance from the FRONT EDGE of this same blood drop to the Convergence (see diagram at right). You can measure in any units, however, you should measure in millimeters in this activity. Step #4 Use the Trigonometry formula below to calculate the Origin. You front edge of blood drop Where did the injury occur along this line? measure this distance Origin is the exact distance along this Convergence line where the injury occurred Convergence is where all the blood drop travel lines intersect will need a scientific calculator OR trigonometry table to complete the Tangent of Blood Drop Impact Angle calculation (see your supervisor for help finding the correct buttons to push on your calculator for Tangent ). Tangent of Blood Drop Impact Angle Distance From Blood Drop To Convergence Example #1: Impact Angle of the blood drop 40 o and the front edge of the blood drop is 38.7cm away from the Convergence. Where is the Origin? BLOOD SPATTER ON THE FLOOR Distance To Point of Origin? Impact Angle 40 o front edge of blood drop Distance to Convergence 38.7cm Tangent of 40 o 0.84 38.7cm 38.7cm 32.5cm The injury occurred exactly 32.5cm above the Convergence! 55
Example #2: Impact Angle of the blood drop 70 o and the front edge of the blood drop is 28.5cm away from the Convergence. Where is the Origin? BLOOD SPATTER ON A WALL Distance to Point of Origin? Distance to Convergence 28.5cm Impact Angle 70 0 Tangent of 70 o 2.75 28.5cm 28.5cm 78.3cm The injury occurred exactly 78.3cm away from the Convergence 4. Look over the Reference Page Trigonometry And Blood Drops Part 2 to get a better understanding of why this Origin formula works. 5. Calculate the Origin for the Training Lab Crime Scene. Use Blood Drop #1 for your calculations. Record your results in Table 1 (located on the Training Lab Crime Scene ) 6. Calculate the Origin for the Training Lab Crime Scene using Blood Drop #2 for your calculations, and then repeat your calculations one more time using Blood Drop #3 for your calculations. Record all results in Table 1. 56
Figure 1 Training Lab Crime Scene Make all measurements in millimeters Table 1 Blood spatter analysis #1 #2 #3 Impact Angle Distance To Point of Convergence (mm) Origin Height (mm) #1 #2 #3 Rock 57
REFERENCE PAGE TRIGONOMETRY AND BLOOD DROPS PART 2 *Recall a Right Triangle and its labels: Angle B side a side c (hypotenuse) Angle C side b Angle A *A Right Triangle is defined when calculating the Origin from blood spatter. Origin Origin Distance (side a ) Distance from blood drop to Convergence (side b ) Convergence Blood Drops Impact Angle (Angle A) Blood Drop *This makes it very easy to calculate the Distance To The Origin for blood splatter! Simple use the Trigonometry Formula: Tangent of Impact Angle (Angle A) (side a ) Distance From Blood Drop To Convergence (side c ) *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 Origin of the blood spatter shown below? Tangent of 70 o 12 inches 2.75 12 inches 33 inches Origin? Blood Drop #2 Blood Drop #1 The injury occurred 33 inches above the Convergence Distance from the front edge of Blood Drop #1 to Convergence 12 inches Impact Angle of Blood Drop #1 70 0 58
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 Origin or the 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 Origin of this single blood drop. Why can t you determine the 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 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 Origin Heights in Table 2 (provided to the right). 5. All three of my Origin Height calculations were (check one): identical similar very different Table 2 - Calculated Origin Heights for Training Lab Crime Scene #1 #2 #3 Origin Height (mm) Average Point of Origin Height (mm) 59
6. Why should you complete calculations using several blood drops (like Blood Drops #1, #2, and #3) rather than simply calculating Distance To Point Of Origin from one drop (like Blood Drop #1 only)? 7. Calculate your Average 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 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) 60
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. The victim was hit times. 10. 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 ( Convergence), and how far away from the wall ( 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. W ALL FLOOR A. How far away from the wall (in inches) was the victim standing when he was shot? The 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 Origin becomes the distance AWAY FROM THE WALL (not the height). Height can simply be measured as the distance from the floor to the Convergence. 61