Metal detectors in crime scene investigations
Metal detectors are electronic devices designed to detect hidden metal objects, playing a crucial role in crime scene investigations and security operations. These devices operate on the principle of electromagnetic induction, which allows them to locate metallic items buried in various materials, including soil. Law enforcement personnel frequently utilize metal detectors to find stray bullets, cartridge cases, and even buried human remains, as well as personal items that may be significant to a crime scene. Their ability to map the positions of metal objects enhances the investigative process.
In addition to their use at crime scenes, metal detectors are employed in airport security to screen passengers for concealed weapons and contraband. Some schools in the United States are also adopting metal detectors to prevent the entry of weapons on campus, reflecting a growing focus on safety in educational environments. Modern metal detectors have become more sensitive, lightweight, and energy-efficient compared to earlier models, featuring advanced capabilities such as metal discrimination and depth detection. Underwater metal detectors are particularly useful for recovering evidence in bodies of water, showcasing the versatility and importance of these devices in various investigative scenarios.
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Subject Terms
Metal detectors in crime scene investigations
DEFINITION: Electronic devices used to detect hidden metal objects.
SIGNIFICANCE: Metal detectors are invaluable tools for law-enforcement and security personnel, enabling the location of hidden metallic objects at crime scenes and related areas as well as the screening of individuals for possible possession of weapons or contraband.
At crime scenes, investigators often need to find metallic objects buried in soil or hidden in other materials. Metal detectors use the principle of electromagnetic induction to detect metal. The simplest detector consists of an oscillator that generates an alternating current that passes through a coil of wire. This produces an alternating magnetic field. When a piece of metal is relatively close to the coil, eddy currents are generated in the metal. The eddy currents produce their own alternating magnetic field, which is detected by a receiver in the metal detector.
Law-enforcement investigators often use metal detectors to locate stray bullets that may have become embedded in flooring, walls, furniture, and other objects at crime scenes and related locations, as well as to find cartridge cases that may have been left behind by perpetrators. Metal detectors are routinely used to map the locations and positions of buried human remains, as such devices can document the spatial positions of coins, belt buckles, eyeglasses, key rings, watches, and other items containing metal that people routinely carry with them. Metal detectors deployed in aircraft are particularly advantageous for locating metallic objects within soils that are underwater or otherwise inaccessible by road or by foot, perhaps because of steep terrain or vegetation cover.
Airport security personnel employ metal detectors as part of airline passenger screening, as the devices enable the detection of concealed weapons and contraband. Handheld detectors can be used to determine the precise locations of metal objects on a person. Although the use of metal detectors for security purposes in public schools is not a standard practice in the United States, some American school districts have begun using the devices as part of their efforts to prevent students from bringing onto school grounds weapons that could be used to commit crimes against other students and faculty.
Since the mid-1990s, metal detectors have become increasingly sensitive and light in weight. Compared with earlier models, the metal detectors available in the early twenty-first century use less battery power, discriminate better among different metals, and locate metallic targets at greater depths. Detectors have been developed that have the ability to indicate the approximate length of metallic objects, enabling security personnel to locate the objects more rapidly and take appropriate action. The best metal detectors are fully computerized. They use microchip technology for setting sensitivity, metal discrimination, tracking speed, filtering of noise, and threshold volume. Values for these parameters are stored in memory for future use. Forensic teams have used underwater metal detectors to discover evidence related to crimes, such as cell phones, that criminals had tossed into swamps, lakes, oceans, and other bodies of water.
Bibliography
Baker-Jarvis, James, et al. Metal Detector Studies: Research Materials. Washington, D.C.: National Institute of Standards and Technology, 2002.
James, Stuart H., and Jon J. Nordby, eds. Forensic Science: An Introduction to Scientific and Investigative Techniques. 2d ed. Boca Raton, Fla.: CRC Press, 2005.
Paulter, Nicholas G. Users’ Guide for Hand-Held and Walk-Through Metal Detectors. Washington, D.C.: National Institute of Justice, 2001.
"Underwater Metal Detectors Help Solve Crimes." Marine Technology News, 5 Mar. 2024, www.marinetechnologynews.com/news/underwater-metal-detectors-solve-635051. Accessed 15 Aug. 2024.