Date of Graduation
Eberly College of Arts and Sciences
Forensic and Investigative Science
Trajectory determination is a very important part of understanding and reconstructing a shooting scene. Conditions for the scene vary for each crime committed, but the evidence left at the scene required to make a reconstruction remains similar. The job of the examiner is to collect the evidence left at the scene and use that evidence to establish what may have happened during the commission of the crime. There is also important information that an examiner may not be privy to, e.g., the firearm and cartridge used. In this case, the evidence that is present, and other gathered information can be used to estimate certain required conditions such as muzzle velocity. There are many external elements that can affect the trajectory of a bullet, such as air resistance, lift, and wind. There are also characteristics of the bullet such as weight, caliber, and shape that can affect the trajectory. At the scene, most often an examiner will collect a bullet and gather impact angle information from a bullet hole to help with trajectory determination.
This project examined the determination of possible trajectories based on examiner measurements at a ‘scene’. A Glock 19 (G19) pistol was used to fire into plywood squares at various angle combinations. This helped to simulate different target placements found at a shooting scene. A combination of four different vertical angles and three different azimuthal angles were for the shooting of the twenty-four boards. Factors such as ricochet and damage resulted in measurements being performed on sixteen boards. Eighteen participants repeated the measuring process three times. All the measurements were analyzed to determine reproducibility. These measurements were used to reconstruct the trajectories. The effect of error in angular measurement on trajectory reconstruction was evaluated.
The results from this study demonstrated that the largest error was associated with the measurement of the azimuthal angles. This is likely due to method of measurement and the skill of the participant. In all but one board the quasi-ground truth measurements were within the 95% confidence ellipse of the data. The study also demonstrated that small changes in the angle measurements can result in a large variations in potential shooter positions as determined by the trajectory calculation.
Poulton, Baillie E., "Computerized Trajectory Analysis for Firearms Examiners" (2023). Graduate Theses, Dissertations, and Problem Reports. 12082.
Available for download on Wednesday, July 24, 2024