Gunshot residue has long been recognized as one of the most prevalent and analyzed types of evidence in violent crime investigations. GSR is the term used to describe the collection of material left behind by a firearm when it is fired. The three main components of GSR are powder, metal, and glass. When firearms are discharged, all three components are ejected from the weapon at high velocity. It is these ejecta that can be found at the scene of the crime.
Guns are an essential tool for self-defense. However, guns also have the potential to cause injury or death if not handled properly. Police departments across the country are trained in gun safety and crime scene photography. They also use laboratory analysis tools to identify the type of weapon used based on physical characteristics of the projectile recovered at the scene. Gunshot residue patterns can also help police investigators determine how many people were present during the crime and possibly even their emotional states (if they had reason to shoot someone). Finally, guns can be cleaned with various substances which may be useful to trace back to its owner.
Evidence collected at the scene of the crime consists mainly of physical items that were touched or handled by persons who were involved in the incident. These items may include bullets, shell casings, knives, hammers, and other weapons.
Forensic Science and Gunshot Residue As a result, investigators must be educated in evidence collecting and have some knowledge of forensic science. Investigators can utilize gunshot residue evidence to corroborate or refute a series of events in which there are no witnesses or clues. For example, if an officer on duty is shot and killed at work but his gun is not found at the scene, gunshot residue evidence could help prove or disprove that he was actually shot by someone else at work.
Gunshot Residue Basics: Powder burns and metal fragments from the projectile cause gunshot residues to become airborne when it enters the body. These particles remain in the air for several minutes and can be captured with various types of equipment. The three main components of gunshot residue are barium, antimony, and copper. Barium is used to mark the location of a firearm within its firing chamber, while antimony is used to identify the type of ammunition fired. Copper is present in both silver and lead bullets because it is part of the alloy used to make the bullet core. When recovered at the crime scene, gunshot residue is often found around the head and shoulder blades because these areas of the body are closest to the source of fire when the gun is discharged.
Crime Scene Photos: Forensic photographers record many details about a crime scene, including the position of the body, the direction of blood spatter, and the presence of any weapons at the scene.
During an inquiry, three major areas are inspected for gunshot residue: the shooter's hands, clothes, and the surroundings surrounding the shooter. Investigators check for gunshot residue on the clothing of everyone who was present during the shooting scenario. They also look for signs that might indicate where on a person it came from. Finally, they search for physical evidence such as shell casings or other objects that may have been fired.
Gunshot residue is made up of particles of metal that come from the gun when it fires. These particles include silver and copper. When firearms fire their ammunition, they expel these metals into the air where they can be spread around the crime scene. The presence of this material doesn't necessarily mean that gunpowder was used in the firearm but not all guns produce gunshot residue.
Copper and silver particles stay in the environment for only about two days, so if you're looking at old gunshot residue evidence, you won't be able to make much of an assessment about what happened recently. However, if you find traces of copper and/or silver on items that were stored away from direct sunlight, then they could still provide information about events that took place more than two days ago.
Investigators use a microscope called a light microscope to view small quantities of materials under low magnification.
Unburned gunpowder, explosive primer, and bullet or cartridge fragments make up the majority of gunshot residue. The issues with the general trustworthiness of gunshot residue stem from the ease with which it may be tampered with and manipulated, rather than the testing or identification of its particles. Gunshot residue can be cleaned off a weapon using soap and water or other cleaning agents, therefore erasing any possible evidence that it was used in a crime.
In addition, because it is present in such low levels, there are many ways to produce it artificially. Laboratory experiments have shown that it is possible to create patterns with shotgun shells similar to those found at crime scenes. This means that if firearms experts cannot find any physical evidence that a gun was fired, they could still conclude that it happened based on the presence of gunshot residue on someone involved in the incident.
Gunshot residue tests themselves have been criticized for being unreliable due to variations in particle size, density, and color between weapons and between shots within one weapon. Because of this, some investigators will fire multiple rounds into evidence to obtain samples large enough for analysis. These concerns can be addressed by using microscopy to analyze sub-samples from around the projectile or about 1/8th of an inch in diameter, which will contain more consistent elements.
The American Society of Crime Lab Directors (ASCLD) reports that gunshot residue tests are considered laboratory quality controls for police laboratories nationwide.