Gunshot Residue

N. Pianelli, D. Martinez, A. Hull, R. Park

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Physical Properties

Gunshot residue often leaves a dark brown or black residue on the shooter's clothes or hands and smells just like gunpowder. It is hard to get this residue off of skin or clothing so it is considered good trace evidence.

Chemical Properties

Gunshot residue is composed of mainly three different elements; barium, lead, and antimony. Less common elements that are found in gunshot residue include aluminum, sulfur, tin, potassium, zinc, and so on. The cartridge case, bullet, bullet coating, and metal jacket also contain specific elements that can be detected. Virtually all cartridge cases are made of brass (70% copper and 30% zinc).

Types of Gunshot Residue

After a gun has been fired it leaves back residue, this residue can be put into one of three categories: degressive/regressive burning, neutral burning and progressive burning. Degressive burning is when the gunpowder forms into flakes, balls and/or sticks. When the grains are single perforated the burning is neutral, but if the grains are multi-perforated the residue is progressive.

How Forensic Analysts analyze gunshot residue

Major methods for detection of GSR are analytical and qualitative. Analytical inclue methods include: Neutron Activation Analysis (NAA), Atomic Absorption Spectrophotometry (AAS), and Inductively Coupled Plasma Mass Spectroscopy (ICP-MS). These methods are used to identify the qualities in the residue, and the elemental composition of the particles of the residue is generated when these methods are used.

In the field 2 main methods are used to collect gunshot residue: the two methods are either using a carbon-coated adhesive stub or an alcohol swab. The stub has fewer false negatives, and the swab is best used for smooth surfaces. The advantages of the stub are that it can directly be applied to the surface to be tested, and the stub with the residue on the surface can be directly prepared to be analyzed to find the surface details for comparison with other known GSR, also pictures can be taken of this.

Crime Lab Gets International Attention

Case Study

The case is called “The Mysterious Case of a Hollywood Star’s Wife.” May 4, 2001, Robert Blake (famous actor) took Bakley to a restaurant for dinner. Later, Bakley was murdered by a gunshot to the head while sitting in Blake’s car, which was parked on a side street around the corner from the restaurant. Bakley was shot once in the right cheek and once in the shoulder. Blake told the police that he had walked his wife to his car and then returned to the restaurant because he had left his revolver (which he carried for protection) under a booth. He said that, when he returned to the car, he found Bakley dead.

No witnesses of the shooting were available. No one at the restaurant remembered seeing Robert Blake return to get his gun.

Detectives swabbed Blake for gunshot residue about two and a half hours after the murder. Five particles of gunshot residue were found on his hands, and more residue was found on his black T-shirt, blue jeans, belt, and boots.

The murder weapon was found the next morning in a garbage dumpster about 6 m from Blake’s car. It was an antique 9 mm Walther P-38 double-action, semi-automatic pistol that had been standard issue for the German army in World War II. The gun had no registered owner, and no fingerprints were found on it.

Months into the investigation, police interviewed two retired stuntmen. Both claimed that Blake tried to hire them to kill his wife.

After nearly a year of investigation, Robert Blake was arrested and charged with the murder of his wife. His long-time bodyguard, Earle Caldwell, was also arrested and charged with conspiracy to commit murder.