Lasers in crime scene investigations
Lasers play a significant role in crime scene investigations by enhancing the detection and analysis of evidence. Their ability to focus sharply allows forensic scientists to uncover hidden materials, such as fingerprints and body fluids, more effectively than traditional optical methods. Techniques like laser ablation-inductively coupled plasma-mass spectrometry enable the rapid and accurate identification of substances by vaporizing small samples and analyzing their mass spectral patterns. Additionally, lasers facilitate noninvasive imaging, allowing for the reconstruction of cranial features and aiding in the identification of individuals. In cases of sexual assault, laser capture microdissection (LCM) isolates sperm cells from complex tissue samples, providing clearer forensic evidence. Raman spectroscopy further aids investigations by characterizing the chemical composition of various materials through frequency shifts in reflected laser light. However, a recent study highlighted that while three-dimensional laser scanning offers detailed crime scene documentation, it is less cost-effective and slower compared to traditional two-dimensional photography. Overall, the integration of laser technology in forensic science enhances the capabilities of crime scene investigations, although practicality and cost remain considerations for their use.
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Subject Terms
Lasers in crime scene investigations
DEFINITION: Sources of intense coherent, monochromatic electromagnetic radiation.
SIGNIFICANCE: Because laser light beams can be sharply focused in a given direction, lasers are very helpful in the detection of hidden evidence at crime scenes or related locations and for use in spectroscopic analysis of evidence samples.
In forensic investigations, the presence of such evidentiary materials as fingerprints, skin, hair, body fluids, and bone fragments is more easily detected with laser light than with other optical devices. When suspected matter in an investigation is coated or injected with fluorescent dyes and then illuminated with the spectral brightness of laser light, atoms in the dyes absorb photons and become excited. Upon de-excitation, the material fluoresces, and photons of a lower frequency are emitted. The fluorescence produces a sharp image of hidden evidence that can be captured on film.
The technique of combining laser technology with mass spectrometry, known as laser ablation-inductively coupled plasma-mass spectrometry, is an accurate, rapid method for identifying evidential substances. An extremely fine laser beam is used to vaporize small amounts of the material inside of a mass spectrometer. By analyzing the mass spectral fragmentation patterns of the components of this vapor, scientists can identify the constituent compounds. This method can be used to differentiate trace amounts of dirt, paint chips, clothing fibers, strands of hair, and pieces of glass. Forensic scientists can use this method to analyze rates of growth in a shaft of hair, which can indicate drug usage or exposure of the subject to materials used to manufacture chemical and biological weapons.
During studies, when it is difficult to obtain fingerprints or dental records of a subject, of the skull can provide important identification information, including information on the individual’s age, sex, height, and general level of health. Lasers can be used to scan skulls and generate three-dimensional reconstructed images of cranial morphology and facial features. Laser scanners do not release radiation, are noninvasive, are fast and accurate, and do not contact the subject material.
Laser capture microdissection (LCM) is used in the forensic investigation of sexual assaults. This method isolates spermatozoa from microscope slides that contain sperm and vaginal cells taken from complex tissue samples. Laser beam energy directed onto a slide can extract sperm cells from the sample and exclude the majority of female (deoxyribonucleic acid) that often contaminates sperm cell analysis in sexual assault cases. LCM may eventually replace preferential lysis as the standard forensic method for processing microscope slide samples.
Raman spectroscopy (RS) is a laser technique that enables forensic scientists to gather detailed information about the chemical composition of evidentiary material. When light from a high-intensity laser is reflected off a material, a small fraction of the reflected light is shifted to a slightly different frequency from the original laser light. The frequency shift identifies the molecular composition of the specimen. RS has proven very useful in identifying fiber, ink, dye, and resin evidence.
According to a 2022 analysis by the National Institute of Justice, the use of three-dimensional laser scanning to record crime scenes was found to be cost prohibitive while being outperformed by two-dimensional photography for accuracy. The study found three-dimensional laser scanning to cost about $852 a minute, while two-dimensional photography cost $126 a minute. At the same time, photography captured information at the scene far faster—an average of about seven minutes—than three-dimension laser scanning, which took an average of ninety-four minutes. When assessed for accuracy, two-dimensional photography was deemed the most accurate, followed by three-dimensional scanning.
Bibliography
Conn, Michael P., ed. Laser Capture Microscopy and Microdissection. Boston: Academic Press, 2002.
"Crime Scene Documentation: Weighing the Merits of Three-Dimensional Laser Scanning." National Institute of Justice, 17 Jan. 2022, nij.ojp.gov/topics/articles/crime-scene-documentation-weighing-merits-three-dimensional-laser-scanning. Accessed 15 Aug. 2024.
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.
Murray, Graeme I., and Stephanie Curran, eds. Laser Capture Microdissection: Methods and Protocols. Totowa, N.J.: Humana Press, 2005.