In a crime scene examination, investigators are responsible for collecting items of evidence and processing the items for possible latent prints. Latent prints are left by chance on a surface when someone touches an item. The latent print represents a partial impression of the unique ridge pattern located on an individual’s fingers and palms.
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Evidence that is collected is categorized as nonporous, semi-porous or porous. Nonporous evidence can include weapons, vehicles, glass bottles, and plastic bags. Semi-porous evidence can include magazines, varnished wood, and some plastic materials. Porous evidence includes paper, unfinished wood, and fabrics.
Latent prints on nonporous surfaces can pose a challenge for investigators because they are very fragile. They consist of 99% water and approximately 1% amino acids, lipids, and other compounds that can easily be wiped away if the evidence is not handled carefully.
Technology Used to Identify Latent Prints
One of the most successful methods used to process nonporous items for latent prints is the superglue method. Superglue fuming involves placing evidence items in an airtight cabinet and using various heating methods to transform a few drops of cyanoacrylate adhesive (superglue) into a vapor. The vapors will adhere to fingerprint residue that may be present on the evidence items forming a white outline of ridge detail.
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The superglue fuming process can take up to 30 minutes from start to finish and results in the partial prints becoming visible. In order to see the print residue more clearly, enhancement techniques are used to create an image that is easier for latent print examiners to evaluate. Some of these techniques include black powder, fluorescent powders, and dye stains. When dye stains are used, the superglued evidence must be dipped in the stain, hung to dry, and visualized under an alternate light source. This extra step adds another day to processing. Additionally, the developed prints must be photographed. Superglue fuming produces excellent results in many cases, but is a very time consuming process.
New Advancements in Finding Latent Prints
New time saving technology has recently been developed by Dr. Kang Liang of the Commonwealth Scientific and Industrial Research Organization (CSIRO). The method involves identifying an item of evidence that may contain latent print residue and adding a small amount of metal-organic framework (MOF) crystals. The crystals bond with the fingerprint residue much like superglue fuming creating an outline of the ridge detail. The reaction happens within 30 seconds and the prints can immediately be viewed with ultraviolet light and digitally photographed.
This new technology has the potential to save crime scene investigators an enormous amount of time. Furthermore, the technique is not limited to a crime laboratory setting, but can be utilized at the crime scene. Rather than collecting multiple items and having to transport the evidence to the crime laboratory for processing, the crystals can be applied to surfaces such as windows, door knobs, and electronics at the actual scene.
About the Author: Dena Weiss is a full-time professor at American Military University, teaching courses in criminal justice and forensic science. She has been a crime scene investigator for more than 20 years and is currently a fingerprint expert for a central Florida police department. Prior to that position, she was a serologist for the Florida Department of Law Enforcement. Her court experience includes testifying in more than 200 federal and circuit court cases in over 15 Florida counties.
Dena has a bachelor’s degree in chemistry and sociology from Mary Baldwin College and a master’s degree in forensic science from Virginia Commonwealth University. She recently earned her Ph.D. in Business Administration with an emphasis in Criminal Justice.