Directed Research Project
Dr. Marilyn Miller
Latent prints can be a valuable source of forensic evidence when solving a crime. They can verify if a person was at a specific scene, identify unknown individuals to connect them to a scene, and help to corroborate eyewitness accounts. Latent prints, however, are not always visible until they have undergone enhancement or visualization techniques. When fired cartridge cases are suspected of containing latent prints, they are brought in for latent print processing before any firearm analysis is performed. As a result, these cartridges are often coated in various residues or dyes when they arrive for firearm examination. In response, this study aimed to determine the visual impact superglue fuming and dye staining visualization methods have on firing pin and breechface impressions.
Two-hundred cartridges were used in this study. Of these, one-hundred cartridges were 9mm and one-hundred cartridges were .40 Smith and Wesson (S&W) caliber. In controlling for material, fifty cartridges of each caliber were brass cartridges, and fifty cartridges of each caliber were nickel. These cartridges were superglue fumed, and dye stained with either Basic yellow, Rhodamine 6G, or MBD to determine the influence these processing methods had on the visibility of firearm impressions. The visibility of firing pin and breechface impressions was dependent upon which dye stain was used after the cartridges have been superglue fumed, and what caliber and material the cartridges were made out of. With nickel .40 S&W cartridges, the use of MBD would be favorable when compared to Basic yellow or Rhodamine 6G to preserve as much fine detail as possible. Oppositely, the use of Basic yellow or Rhodamine 6G would be preferable to MBD when analyzing brass .40S&W cartridges. All three dye stains could be used when processing nickel 9mm cartridges, as none of them significantly obscured the striations or shearing found on the cartridge. However, when used on the brass 9mm cartridges, all three dye stains significantly concealed the fine details needed to successfully compare the cartridge to potential test fires. It is important to note that cleaning the cartridges with acetone did effectively eliminate the influence of these visualization methods on breechface impressions and recoil action striations.
Overall, this study was an introductory look into the influence latent print processing techniques have on firearm analysis. Moving forward, studies should be conducted using different enhancement techniques, such as black powder, to determine the impact they have on firing pin and breechface impressions. Eventually, a study in which processed cartridges can be entered into NIBIN would be beneficial to determine if NIBIN technology is able to differentiate between latent print dye residue and firearm toolmarks.
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VCU Master of Science in Forensic Science Directed Research Projects
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