Latent evidence
Latent evidence refers to physical markings left behind unintentionally by individuals, primarily in the form of fingerprints, palm prints, and sole prints. This type of evidence, composed of naturally secreted materials such as sweat and skin oils, can be found on both porous surfaces, like fabrics, and nonporous surfaces, such as glass. Latent evidence is significant in criminal investigations as it provides crucial leads, particularly when traditional evidence is scarce. Unlike visible prints, which are easily seen, latent prints require special techniques for recovery and analysis.
Various methods exist to enhance and collect latent evidence, including physical, chemical, and instrumental techniques. Physical methods involve using powders and brushes, while chemical methods include dye-staining and reagents that react with biological materials. Each technique is chosen based on the type of surface where the evidence is found, and the prints are meticulously documented through photography. This sophisticated approach allows law enforcement personnel to maximize their chances of successfully retrieving vital evidence that could help solve crimes.
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Latent evidence
SIGNIFICANCE: Modern techniques of recovering latent evidence offer personnel in law enforcement increased opportunities to find evidence that can be used to solve crimes.
Fingerprints, palm prints, and sole prints are examples of latent evidence composed of naturally secreted materials, such as sweat, lipids, and sebum (skin oil) that human hands and feet may deposit on surfaces with which they come into contact. Latent evidence may be deposited on both porous surfaces, such as fabrics, and nonporous surfaces, such as glass. However, evidence on porous surfaces is generally likely to last longer than that on nonporous surfaces because it may soak into the porous surfaces.
Latent prints may be distinguished from visible prints, such as bloodstains that are transferred from nonporous sources to materials such as carpeting. Latent evidence also is distinguished from what are known as plastic, or three-dimensional, prints, which are created when friction ridges come into contact with softer surfaces and make three-dimensional impressions into the softer surfaces.
Collection Techniques
Latent prints are enhanced or visualized, prior to collection, using physical, chemical, or instrumental methods. All prints are photographed prior to performing other visualization techniques. Physical methods of collection include the use of certain colored powders and brushes. Prior use of cyanoacrylate (chemical adhesives such as superglue) fuming enhances the effectiveness of physical visualization methods. Physical methods are used for dry nonporous surfaces. Once visualized, the latent prints are photographed a second time. The latent prints are then lifted, placed on backing cards and documented.
Chemical methods can be used for processing prints on both dry and wet surfaces. For dry surfaces, certain dye-staining techniques, using substances such as gentian violet, fluorescent materials, and other laser-excitable materials, are used, followed by lighting or laser excitation, followed by photography of the developed prints. On wet surfaces, small-particle reagent sprays or physical developers are used. On porous surfaces, the chemicals react with the biological evidence, not with the surfaces. Numerous techniques and substances are used, including silver nitrate and ninhydrin.
Latent prints even can be lifted from the skin of victims of a homicide. Such prints are collected using glue fuming, with or without the transfer lift technique using magnetic fingerprint powder. This technique involves directing the fumes from heated glue onto the skin.
Bibliography
Baxter, Everett. Complete Crime Scene Investigation Handbook. Boca Raton: CRC P, 2015. eBook Collection (EBSCOhost). Web. 26 May 2016.
Cole, Simon A. Suspect Identities: A History of Fingerprinting and Criminal Identification. Cambridge, Mass.: Harvard University Press, 2001.
Gilbert, James N. Criminal Investigation. New York: Prentice Hall, 2004.
James, Stuart H., and Jon J. Nordby. Forensic Science: An Introduction to Scientific and Investigative Techniques. Boca Raton, Fla.: CRC Press, 2003.
Kasper, Stephen P. Latent Print Processing Guide. London: Academic P, 2016. eBook Collection (EBSCOhost). Web. 26 May 2016.
"Laboratory Operations Manual Examination of Latent Print Evidence." Drug Enforcement Administration, 20 Nov. 2023, www.dea.gov/sites/default/files/2023-11/LOM%207700%20-%20Examination%20of%20Latent%20Print%20Evidence.pdf. Accessed 8 July 2024.
Lee, Henry C., T. Palmbach, and M. T. Miller. Henry Lee’s Crime Scene Handbook. New York: Academic Press, 2001.
Zarwell, Lucas and Gregory Dutton. "The History and Legacy of the Latent Fingerprint Box Study." National Institute of Justice, 19 Sept. 2022, nij.ojp.gov/topics/articles/history-and-legacy-latent-fingerprint-black-box-study. Accessed 10 July 2024.