Fingerprints Fall 2019_SAR FINAL.pdf - SCI 114 u2013...

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SCI 114 Scientific Principles of Forensic Science Page 1 Laboratory Exercise: Fingerprint Analysis Name: ______________________________ Date:___________________ Section# ________ 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). i,ii 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 . iii 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 . iv,v 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. 3 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 types 3 ( see Figure 1 6 ). Loops enter from one side of the fingerprint, recurve, 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 3 ( see Figure 2 6 ). Figure 2: Loop Patterns. Figure 1: Arch Patterns.
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SCI 114 Scientific Principles of Forensic Science
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