TRAINING LAB BLOOD AS EVIDENCE BLOOD DROPS FALLING AT AN ANGLE NAME

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Lucy Taylor
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1 TRAINING LAB BLOOD AS EVIDENCE BLOOD DROPS FALLING AT AN ANGLE NAME Background: You just completed studying the behavior of passive blood drops that drip straight down from a wound, but not all blood drops fall straight down. Blood drops often travel at angles before hitting a surface and forming blood spatter. For example: blood drops flying away from a wound just made by a gunshot or blow. blood drops falling from a moving victim. blood drops that are flying from a swinging weapon. d blood drops appear oval in shape when they hit a surface and their unique shape can help you determine the direction they were flying. A collection of angled blood drops (blood spatter) in a room can help you determine where a victim was injured in a room even if the victim is no longer present. In this Training Lab you will be investigating the behavior of d Blood Drops falling at different angles. 1. You will be trained to observe a blood drop that fell at an angle and determine the direction it was moving. 2. You will be trained to observe a blood drop that fell at an angle and determine its of Impact or Impact. Procedures: Part 1 Collecting Blood Drops Released From Different s 1. You will need a clipboard, NINE large note cards, a covered beaker of simulated blood, a dropper, a meter stick, a protractor, a roll of masking tape, and a small stack of books. 2. When a blood drop falls straight down, or hits a wall 90 o straight on, it contacts the surface at a 90 o angle. 90 o floor wall A blood drop striking the floor or wall at a 30 o angle would look something like this: 30 In this Training Lab you will observe blood drops striking a surface o at several different angles. To simulate blood dropping at different angles you will adjust the angle of the surface the blood drops are hitting. 3. Place the clipboard on a flat table. Tape the LONG EDGE of the clipboard to the table (using pieces of tape like hinges) so you can tilt the clipboard up and down at different angles (see Figure 1 below). read angle here Figure 1 How to set up the clipboard to test angled blood drops protractor in correct position note card tape hinges floor 30 o 10 o 20 o note card wall place clipboard clip on opposite side from protractor place books behind to support the clipboard 37

2 4. Tape TWO of the large note cards on the clipboard, side by side. Orient the cards on the clipboard as shown in Figure Label one of the note cards 10 o in the upper right corner along with your name. Label the second note card 20 o in the upper right corner along with your name. 6. Place the EXACT CENTER of the protractor s flat edge (usually indicated by a line coming from a hole) next to the hinged edge of the clipboard (see protractor in correct position in Figure 1). The numbers along the curved edge of the protractor will tell you the angle the clipboard is raised (see read angle here in Figure 1). This number is NOT the angle the blood drop will be falling. 7. Carefully tilt the clipboard so it is tilted at an 80 o angle in relation to the tabletop (almost straight up and down). The edge of the clipboard should be next to 80 on the protractor. Place books behind the clipboard to hold it in position at this exact angle. 8. A drop of blood released from above the 80 o tilted clipboard will hit the note card at a 10 o angle (see the diagram at right). 9. Suck up simulated blood into the dropper (avoid sucking up bubbles). All drops will be released from EXACTLY 15 inches above the tabletop (hold a meter stick upright on the table next to the clipboard to measure 15 inches high). 10. Hold the open end of the dropper over the 10 o note card. Gently squeeze the dropper to release THREE separate drops of blood from 15 inches each drop falling on a different location of the 10 o card (the drops should not touch or overlap). You should NOT allow bubbles to form as you release drops. Add additional drops if any bubbles are present, or any drops overlap. 11. Leave the card on the clipboard and lower the clipboard slightly so it is now tilted at 70 o (measured with the protractor) and support from behind with books. This means falling blood drops will hit the note card at a 20 o angle. 12. Release three drops of blood from 15 inches above the tabletop clipboard blood drop so they will hit the 20 o note card. Add additional drops if any bubbles are present, or any drops overlap. 13. Lower the clipboard and carefully remove the two note cards with blood drops. Place the note cards with wet blood drops on a flat surface where they can dry without being disturbed. 14. Repeat the above steps to drop blood on labeled note cards from the remaining angles: 30 o note card clipboard set to a 60 o angle 40 o note card clipboard set to a 50 o angle 50 o note card clipboard set to a 40 o angle 60 o note card clipboard set to a 30 o angle 70 o note card clipboard set to a 20 o angle 80 o note card clipboard set to a 10 o angle 90 o note card clipboard flat on the table (0 o angle) 16. Clean up your lab station and make sure all your note cards with wet blood drops are in a flat, safe area while they dry. 80 o clipboard 70 o 10 o 20 o table blood drop table 38

3 Part 2 Analyzing Blood Drops Released From Different s IT IS POSSIBLE TO DETERMINE IF A BLOOD DROP WAS TRAVELING AT AN ANGLE WHEN IT HIT THE SURFACE 1. Observe the shapes of your blood drops that fell straight down ( 90 o angle card) and compare them to the shapes of your other blood drop cards that fell at an angle ( 80 o to 10 o angle cards). You should be able to look at the shape of a blood drop and tell if it fell straight down or fell at an angle. Draw a neat sketch, in Table 1, to show the characteristic shape of one of your blood drops that fell straight down. For comparison, also draw a neat sketch, in Table 1, to show the characteristic shape of one of your blood drops that fell at an angle. IT IS POSSIBLE TO DETERMINE THE DIRECTION A BLOOD DROP WAS TRAVELING WHEN IT HIT THE SURFACE 2. Draw arrows on your 80 o to 10 o note cards to indicate the direction the blood drops were traveling when they hit the card at an angle. 3. Observe the shapes of the blood drops that fell at angles. You should be able to tell the direction a blood drop was traveling by the general shape of the blood drop. Blood drops that fall at an angle are stretched out, with one end more rounded and the opposite end more pointed. The pointed end will be pointing in the direction the blood drop was traveling when it hit the surface (the pointed end will be pointing AWAY from the source of the blood drop). The pointed end may also have a drip or tail extending beyond the blood drop. Also, if there are any satellites present they will be located around the pointed end of the blood drop (pointing AWAY from the source of the blood drop). 4. Draw TWO neat sketches, in Table 2. One sketch should show the characteristic shape of one of your 20 o angled blood drops, and the second sketch should show the characteristics of one of your 50 o angled blood drops. Label each sketch with its correct angle, and include an arrow next to each sketch to show the direction the blood drop was traveling when it hit the surface. IT IS POSSIBLE TO DETERMINE THE IMPACT ANGLE OF A BLOOD DROP 5. Pull out your 10 o note card. You should be able to look at the shapes of the blood drops on this card and tell the drops fell at an angle, and even use drop shape to determine the direction the blood drops were falling when they hit the card. But, what if you wanted to know the ANGLE OF IMPACT or IMPACT ANGLE of the drops (both names simply mean the angle that the drop hit the surface). Of course, you know the Impact is 10 o because you set it up this way. But, what if you didn t know the angle? The shape of the drop can also help you determine the Impact. 6. Use a small millimeter ruler and accurately measure, in millimeters to the nearest 0.5mm, the WIDTH (at the drop s widest point) and length LENGTH of each of the three blood drops you dropped at a 10 o Impact. DO NOT include spikes, satellites, or tails in your length measurements length (see sketch at right). Record these measurements in Table 3 Calculating The Impact Of Blood Drops. 39

4 7. Repeat Step #6 and measure the WIDTH and LENGTH of all blood drops collected on all your note cards. Record all measurements in Table Calculate and record (in Table 3) the Average Blood Drop WIDTH (from your three width measurements) and Average Blood Drop HEIGHT (from your three length measurements) for the drops collected on your 10 o card. Round your calculations to hundredths (2 decimal places). 9. Repeat Step #8 and calculate the Average WIDTH and LENGTH for the drops collected on all your note cards. Record these calculations in Table Finally, use the Trigonometry Formula below to calculate the Impact for the drops on your 10 o card. Use your Average Width and Average Height numbers when completing this calculation. You will need a scientific calculator to complete the Inverse Sine calculation (see your supervisor for help finding the correct buttons to push on your calculator for Inverse Sine ) OR simply use a Trigonometry Table that contains Inverse Sine. Round your Impact calculations to the nearest, whole degree. Record your Calculated Impact in Table 3. Impact of Blood Drop (Approximate) = Inverse Sine of Width of Blood Drop Length of Blood Drop Example: The width of the blood drop = 5mm, the length of the blood drop = 36mm 5mm Impact of Blood Drop = Inverse Sine of 36mm Impact of Blood Drop = Inverse Sine of 0.14 Impact of Blood Drop = 8 o (the blood drop hit the surface at an 8 o angle) 11. Repeat Step #10 and calculate the Impact for the drops collected on all of your note cards. Record these calculations in Table Look over the Reference Page Trigonometry and Blood Drops Part 1 to get a better understanding of why this strange Impact formula works! 40

5 Table 1 How to tell if a blood drop fell at an angle by its shape Characteristic Shape Of On Of My Blood Drops That Dropped Straight Down Characteristic Shape Of One Of My Blood Drops That Fell At An Table 2 How to tell the direction a blood drop was moving by its shape Characteristic Shapes Of Two Of My Blood Drops That Helps Indicate The Direction It Was Moving Table 3 Calculating the Impact of blood drops Actual Impact Drop 1 Width Drop 2 Width Drop 3 Width Average Width Drop 1 Length Drop 2 Length Drop 3 Length Average Length Ave. Width Ave. Length Calculated Impact 10 o 20 o 30 o 40 o 50 o 60 o 70 o 80 o 90 o 41

6 REFERENCE PAGE TRIGONOMETRY AND BLOOD DROPS PART 1 *Trigonometry is a useful math that can help you determine unknown angles and unknown side lengths around a Right Triangle (a triangle with one of its angles being 90 o ). *A Right Triangle is usually labeled like this: B side a side c (hypotenuse) 90 o angle a Right Triangle C side b A *PROBLEM - If you knew that A = 10 o and that side c was 1 foot long you could easily calculate the length of side a using the trigonometry formula: sine of A = length of side a length of side c sine of 10 o = length of side a 1 foot 0.17 = length of side a 1 foot 0.17 feet = length of side a Think of sine in the above formula like a conversion factor that converts the unit degrees of an angle (10 o in this problem) into units of length (0.17 in this problem) so the problem can be worked correctly. *Scientific calculators have a sine button that will complete the conversion for you otherwise you would have to look up the conversion on a chart. *You may have also heard of cosine, and tangent. These also work like conversion factors to convert degrees of an angle into units of length in trigonometry formulas. We will only be using sine and will NOT be using cosine or tangent in this Training Lab. *PROBLEM If you knew that side a was 5cm long and that side c was 15cm long you could easily calculate A using the trigonometry formula: A = Inverse sine of length of side a length of side c A = Inverse sine of 5cm 15cm A = Inverse sine of 0.33cm A = 19 o Inverse sine in the above problem is just the opposite of sine. It converts the unit of length (0.33cm in this problem) into the unit degrees of an angle (19.3 o in this problem). *Scientific calculators have an Inverse sine button that will complete the conversion for you. The Inverse sine of 0.33 = 19.3 o SO what does all this have to do with blood drops?? Flip over to the next page and see! 42

7 *When a blood drop hits a surface at an angle, it can be defined by an upside-down, right triangle! direction the blood drop was moving C side a B blood drop side c side b A A = blood drop s Impact side c = Length of blood drop side a = Width of blood drop *This makes it very easy to calculate the Impact of any blood drop you find! Simply use the formula: IMPACT ANGLE ( A) = Inverse sine of width of blood drop side a length of blood drop side c *What is the Impact of this blood drop? length = 12mm width = 5.5mm IMPACT ANGLE ( A) = Inverse sine of 5.5mm 12mm IMPACT ANGLE ( A) = Inverse sine of 0.46mm find the Inverse sine of 0.46 IMPACT ANGLE = 27 o 43

8 Table of Sine and Tangent Values 1. To find the Sine or Tangent of an, simply look up the angle and move over to the correct column. 2. To find the Inverse Sine of a number, simply look up the number in the Sine/Inverse Sine column and move over to the column. Sine Inv. Sine Tangent Sine Inv. Sine Tangent Sine Inv. Sine Tangent

QUESTIONS BLOOD DROPS AS EVIDENCE BLOOD DROPS FALLING AT AN ANGLE

Draw a neat arrow next to each blood drop to indicate the

Which group of blood drops do you think is easier to tell their

blood drops that fell at a 10 o to 40 o angle B.

Why do you need to use Inverse sine rather than just sine when

Complete the following table by writing in your Calculated Impact

Actual Impact s Of Blood Drops 10 o 20 o 30 o 40 o 50 o 60 o 70 o

9 QUESTIONS BLOOD DROPS AS EVIDENCE BLOOD DROPS FALLING AT AN ANGLE NAME 1. Observe the eight blood drops below. Draw a neat arrow next to each blood drop to indicate the direction the blood drop was traveling when it hit the surface. 2. Which group of blood drops do you think is easier to tell their direction of travel? (circle one) A. blood drops that fell at a 10 o to 40 o angle B. blood drops that fell at a 50 o to 80 o angle 3. Why do you need to use Inverse sine rather than just sine when calculating the Impact of a blood drop? 4. Complete the following table by writing in your Calculated Impact s for your blood drops. Actual Impact s Of Blood Drops 10 o 20 o 30 o 40 o 50 o 60 o 70 o 80 o 90 o My Calculated Impact s For Blood Drops Draw a neat STAR below the Calculated Impact s you think were the most accurate. Draw a neat FROWNY FACE below the Calculated Impact s you think were the least accurate. 45

10 5. List TWO errors that could possibly account for any inaccurate Calculated Impact s while completing this Training Lab. 6. Determine the Impact s of the following blood drops. Remember you DO NOT include tails when measuring length! PLEASE SHOW YOUR WORK. Impact = Impact = Impact = Impact = Use the blood drops below to answer Questions #7 - #10. A B C D E F 7. A victim is bleeding from their shoulder and left behind blood drops B, D, and E. Which of these blood drops came from this victim when they were: running fast, walking, and running medium? Choose from drops B, D, and E only! running very fast? walking? running medium speed? 8. Which blood drop came from a person standing still and bleeding from their head? 9. Which blood drop came from a person standing still and bleeding from their knee? 10. A victim, bleeding from both their head and their knee, is running and leaving blood spatter drops D and F behind on the tile floor. Which drops most likely came from : their head? (choose D or F) their knee? (choose D or F) 46

OFFICIAL POLICE REPORT

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