Abstract

When investigating crimes involving gunshots and bullet holes, crime scene technicians must be cognizant of holes and defects in rubberized plastic-composite materials used in most new cars' bumpers, fascias and guard strips and investigate accordingly to determine if the damage was caused by a bullet. Accurate measurements of well-formed bullet holes are necessary to properly determine the angle of impact.

Scenario

An argument in a crowded shopping center parking lot leads to an exchange of gunfire between two rivals that resulted in the death of one of the men. Witnesses at the scene provided conflicting accounts of the incident. Some said each man fired one shot at close range. Others reported hearing only one shot. The surviving participant claimed the victim fired at him first. Crime scene techs who processed the scene recovered and documented evidence accounting for the shot fired by the first man but cannot account for the shot fired by the second man, the victim of the homicide.

Overview

During a recent crime scene tech training session on shooting incident reconstruction, an interesting facet of bullet holes in the plastic-composite door guard strip on the car door panels used for the training session was noticed. In preparation for the training, instructors fired several bullets at different angles, known and unknown, at car door panels. After classroom lecture and exercises, the crime scene tech "students" examined the holes in the door panels to determine the trajectory and angle of impact of the fired bullets.

The door panels used during the training session were scrap parts from old, accident-damaged Lincoln police cruisers. The panels were equipped with rubber-plastic composite bumper guard strips. These strips run the length of the door panel just under the "LINCOL" decal.

While these bumper guards were not the specific intended targets of the test-fired bullets, a few of the shots struck and penetrated these plastic-composite strips. In examining this damage more closely, several techs noted the entrance "wounds" in the plastic material appeared markedly different than the bullet strikes in the metal door panel. The elasticity of the plastic material did not leave what would be considered a characteristic bullet hole.

To determine the approximate angle of impact and trajectory, the crime scene techs used the trigonometric relationship of the width and the length of the bullet hole.

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Related Content

• A Practical Guide to Shooting Scene Preservation for Crime Scene Investigators, by Charles S. DeFrance and Carlo J. Rosati
• Bullet Trajectories at Crime Scenes, by Don Penven
• A "Hands On" Approach to Understanding Gunshot Residue, by Missouri State Highway Patrol
• Firearm Identification in the Forensic Science Laboratory, by Robert M. Thompson