Forensic Shooting Reconstruction Laboratory Exercise

Laboratory Exercises Angle Calculations Angle Measurements Distance Determination Based on Angle of Impact Angle Determination Based on Shotgun Pattern Distance Determination Based on Shotgun Pattern

Angle Calculations When measuring the angles of impact using a trajectory rod and protractor, it is important to have the protractor in a horizontal position. Use the level to ensure the protractor is horizontal.

Angle Calculations After the protractor has been leveled, a plumb bob can be dropped from the trajectory rod past the protractor. Using a ruler, the opposite (O) side (string) can be measured. The distance from the impact to where the trajectory rod and string intersect is the hypotenuse (H). The vertical angle can be calculated using the formula: Sin Θ = O/H The horizontal angle can be read directly from the protractor. Two strips of tape should be used to secure the blocks to the wall. Use caution when placing the blocks in the classroom for the exercise because the tape may remove paint from the wall. Tape residue can be removed with Goo Gone or similar solvent. Marks may be made on the wall to locate the blocks in case they fall off. Remind students that a +/- 5% variance should be incorporated in their results. Note: Angle measurements should be reported with a variance of +/- 5%

Angle Measurements The horizontal angle is measured using the same technique as demonstrated previously. The vertical angle of the impact can be measured with an angle finder.

Distance Determination Based on Angle of Impact Once the angle has been determined, it can be plotted on graph paper to determine the possible distance of the shooter. The measurements must be to scale. In this example, the impact is two feet from the ground. Two blocks on the graph paper equals one foot.

Distance Determination Based on Angle of Impact In this example, the vertical angle was measured at 32 degrees +/- 5 degrees. On graph paper, project the cone of variance of the angle of impact.

Distance Determination Based on Angle of Impact The distance from the wall can now be plotted to the same scale used to locate the impact height. x x x x x x x x 2 4 6 8 10 12 14 16

Distance Determination Based on Angle of Impact Now the height can be plotted to scale on the Y axis. 6 x 4 x 2 x x x x x x x x x 2 4 6 8 10 12 14 16

Distance Determination Based on Angle of Impact The height of the rifle will be based on witness information that the suspect was shooting from the shoulder and that he was 5 foot tall. The max height the rifle could be positioned would be 5 feet. The minimum height for the rifle would be 3 feet. Those ranges can be plotted on our graph. 6 x 4 x 2 x Students may want to use colored pencils on the graph for clarity. x x x x x x x x 2 4 6 8 10 12 14 16

Distance Determination Based on Angle of Impact The overlapping areas of the rifle height and cone of variance demonstrate possible ranges of the rifle. In this example, the shot could have been fired from 1 to 5 feet away. 6 x 4 x 2 x x x x x x x x x 2 4 6 8 10 12 14 16

Angle Determination Based on Shotgun Pattern In the first part of this exercise you will be presented with a shot pattern recovered from a house. By taking measurements of the Height and Width of the shot pattern, the angle can be calculated. Calculate the angle by using the formula: Sin Θ = Height/Width

Angle Determination Based on Shotgun Pattern Once the angle of the shot has been calculated, you will have to determine if the evidence supports the claim of the home owner. The possible angles of the shot must be determined by examining the diagram provided by the police. This can be done using a protractor.

Angle Determination Based on Shotgun Pattern The first measurement is from the right side of Home Owner A’s window. This angle measures 45 degrees from left to right.

Angle Determination Based on Shotgun Pattern The second measurement is from the left side of Home Owner A’s window. This angle measures 60 degrees from left to right. Therefore, if the angle falls within 45 and 60 degrees from right to left, it is possible that the shot came from the direction of the window.

Distance Determination Based on Shotgun Pattern After determining the angle of the shot, we can approximate the distance of the shotgun to the wall. To do this, we use the measurement of the height The height will be considered the radius and used to compare to our known test patterns. Remember that distances are given in ranges, not exact feet. During this time, you can show students the test patterns that were printed from the CD. It is important that the patterns were printed in a 1:1 scale. This can be verified with a ruler. If the PDF files printed smaller than expected, the printer settings were incorrect. When printing in Adobe, the print properties must have the “Page Scaling” set to NONE.