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Unformatted text preview: Laboratory Exercise: Fingerprint Analysis Introduction: Fingerprints No two individuals have identical fingerprints and this uniqueness allows fingerprints to be used in all sorts of ways, including background checks, biometric security, mass disaster identifications, and criminal investigations. Fingerprint analysis has been used to identify suspects and solve crimes for more than 100 years, and it remains an extremely valuable tool for law enforcement and forensic science. One of the most important uses for fingerprints is to help investigators link one crime scene to another involving the same person. In addition, fingerprint identification helps investigators to track a criminal’s record (previous arrests and convictions). All fingers, palms, toes, and feet are covered in raised portions of the skin, arranged in connected units called friction ridges. When these ridges contact a surface, they leave a mark, or an impression called a fingerprint. A fingerprint usually appears as a series of dark lines that represent the high, raised portion of the friction ridge skin known as ridges, while the valleys between these ridges appear as white spaces and are the low, shallow portion of the friction ridge skin known as furrows. The imprint of a fingerprint consists of natural secretions (composed of mainly water, oils, and salts) of the sweat glands that are present in the friction ridge of the skin. Anytime an object is touched, traces of these substances are left behind in the unique pattern of an individual’s friction ridges. Fingerprints are grouped into three general patterns—
arches, loops, and whorls—depending on the shape of the ridges: Arches have ridges that enter from one side of the fingerprint, rise in the center of the fingerprint, and exit the opposite side from which it entered; this resembles a wave-‐like pattern. Tented arches rise to a sharper point than plain arches. Arches make up about five percent of all pattern types3 (see Figure 1). Figure 1: Arch Patterns. Loops enter from one side of the fingerprint, re-‐curve, and exit the same side from which they entered. Loops can be subdivided into two categories; ulnar loops and radial loops. Their designation is based upon if the loop opens toward the little finger or towards the thumb. If the opening is towards the little finger, it is known as an ulnar loop. If the opening is towards the thumb, it is known as a radial loop. Loops account for approximately 60 percent of all pattern types (see Figure 2). Figure 2: Loop Patterns. SCI 114: Summer 2020 -‐ Fingerprints 1 Whorls form circular or bulls-‐eye patterns, like tiny whirlpools, with at least two deltas (triangles). There are four categories of whorls: plain (concentric circles), central pocket loop (a whorl in which an imaginary line drawn between the two deltas does not touch or cross the central pocket), double loop (two loops that create an S-‐like pattern), and accidental loop (irregular shaped). Whorls account for approximately 35 percent of all pattern types (see Figure 3). Analysts use the general pattern type (loop, whorl or arch) to make initial comparisons and include or exclude a known fingerprint from further analysis. To compare a fingerprint, the analyst uses minutiae, or ridge characteristics, to identify specific points on a suspect fingerprint with the same information in a known fingerprint (see Figure 4). For example, an analyst comparing a crime scene fingerprint to a fingerprint on file would first gather known fingerprints with the same general pattern type, then compare the fingerprints side-‐by-‐side to identify specific minutiae that are consistent between the known and unknown print. If enough details correlate, the fingerprints are determined to be from the same person. Figure 4: Minutiae Patterns. There are three types of fingerprints found by investigators at a crime scene. Patent fingerprints, or visible fingerprints, are left on a smooth surface when blood, ink, or some other liquid comes in contact with the hands and is then transferred to that surface. Plastic fingerprints are indentations left in some soft material such as clay, putty, or wax. Latent fingerprints, or invisible fingerprints, are formed when the body’s natural oils and sweat on the skin are deposited onto another surface. Latent fingerprints can be found on a variety of surfaces; however, they are not readily visible. Their detection often requires the use of various methods to develop the fingerprint in order to become visible. For example, they can be visualized by dusting with powders or applying specific reagents. SCI 114: Summer 2020 -‐ Fingerprints 2 Latent Fingerprint Development Techniques Dusting: One of the most common methods for visualizing and collecting latent fingerprints is by dusting a smooth or nonporous surface with fingerprint powder. Powder brushed lightly over a latent-‐bearing surface will cling to grease or moisture in the ridges of a latent fingerprint, making it visible against the background. A powder that will contrast with the color of the surface must be used. If any fingerprints appear, they are to be photographed and then lifted with clear adhesive tape. The lifting tape is then placed on a latent lift card to preserve the fingerprint. Cyanoacrylate: Another common latent fingerprint development technique is cyanoacrylate (superglue) fuming of a surface, which is used prior to applying powders or dye stains. This process is typically performed on non-‐porous surfaces and involves exposing the object to cyanoacrylate vapors. The vapors will adhere to fingerprint impressions present on the object, creating a white impression. Several post-‐cyanoacrylate dye stains or powders may be applied to improve the visualization of the developed detail. Chemical Developers: Porous surfaces, such as paper, are typically processed with chemicals, including ninhydrin and physical developer, to reveal latent fingerprints. These chemicals react with specific components of latent fingerprint residue, such as amino acids and salts. Ninhydrin causes fingerprints to turn a purple color, making them easily visible and they can be photographed. When iodine crystals are subjected to a slight amount of heat, they vaporize rapidly and produce violet fumes. Upon contact with fatty or oily matter, the fumes are absorbed, which develops the fingerprint and it appears yellowish-‐brown against the background. Iodine-‐fumed fingerprints are not permanent and begin to fade once the fuming is stopped. Therefore, it is necessary for the operator to have a camera ready to immediately photograph the fingerprints. Other Collection Methods: In addition to the methods identified above, there are many other techniques for collecting fingerprints from wet surfaces, skin, clothing, wood, and other difficult surfaces. One of these alternative methods is the use of Crystal Violet dye, which can be useful on adhesive tapes since conventional powders adhere to the entire sticky side of the tape, regardless whether a fingerprint is present or not. SCI 114: Summer 2020 -‐ Fingerprints 3 Experiment: Analysis of an Unknown Fingerprint Objectives: Identification of an Unknown Procedure: 1. The students will receive a photograph of an unknown fingerprint as evidence. 2. Analyze the fingerprint(s) from the evidence for general classification (loop, whorl, arch, not identified). 3. Analyze the fingerprint(s) from the evidence for different minutiae. 4. Compare the unknown evidence to the suspect exemplars. Determine the fingerprints’ general classification to narrow down the suspect list. Next examine the minutiae to individualize the fingerprint. Make a conclusion to the identity of the fingerprint associated to your evidence and report your findings. 5. Incorporate the photographed unknown fingerprint and known comparison fingerprint into the laboratory analysis report. Using Microsoft Paint or similar a software program (i.e. Adobe Photoshop), use the highlighting tools (i.e. circles or squares) to highlight six minutiae points that are located in BOTH the unknown and the exemplar. Label the minutiae and classify the fingerprints in the laboratory analysis report. SCI 114: Summer 2020 -‐ Fingerprints 4 References A Simplified Guide to Fingerprint Analysis. (n.d.). National Forensic Science Technology Center (NFSTC). Retrieved from -‐scene-‐
investigator.net/SimplifiedGuideFingerprints.pdf Bertino, A., & Bertino, P. (2011). Forensic science: fundamentals and investigations. South-‐
Western Educational Pub. Division -‐ International Association for Identification (CBD-‐IAI). Retrieved from Federal Bureau of Investigation (U.S.) (1984). The Science of Fingerprints: Classification and Uses. U.S. Government Printing Office. Fingerprint Analysis. (2004). Bergen County Technical Schools. Retrieved from Fingerprint recognition. (n.d.). National Science and Technology Council (NSTC), Committee on Technology, Committee on Homeland and National Security, Subcommittee on Biometrics. Retrieved from -‐
recognition.pdf Fisher, B. A., Tilstone, W. J., & Woytowicz, C. (2009). Introduction to criminalistics: the foundation of forensic science. Academic Press. Holder, E. H., Robinson, L. O., & Laub, J. H. (2011). The fingerprint sourcebook. US Department. of Justice, Office of Justice Programs, National Institute of Justice. Retrieved from Latent Fingerprint Processing Techniques -‐ Selection & Sequencing Guide. Chesapeake Bay Lipton, J. (2014). Fingerprints: Unique to us all. Retrieved from -‐unique-‐to-‐us-‐all/ Saferstein, R. (2015). Criminalistics: An introduction to forensic science. SCI 114: Summer 2020 -‐ Fingerprints 5 ...
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- Fall '19
- Dr. Li
- analyst, developer, Cyanoacrylate, Bertino