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Chapter 6

Chapter 6. Fingerprints. Objectives. Students should gain an understanding of: The characteristics that permit fingerprints to be used for personal identification Methods used to develop latent fingerprints Methods used to visualize fingerprints The classification of fingerprints

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Chapter 6

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  1. Chapter 6 Fingerprints

  2. Objectives • Students should gain an understanding of: • The characteristics that permit fingerprints to be used for personal identification • Methods used to develop latent fingerprints • Methods used to visualize fingerprints • The classification of fingerprints • The use of fingerprints for biometric identification

  3. Introduction • Pattern evidence: items left at a crime scene that may have arisen from different events but that share an identifiable pattern • When pattern evidence is found, it often can be individualized. • The pattern may be so unique that it could be generated by only one source.

  4. History of Fingerprinting (1 of 3) • Alphonse Bertillon’s anthropometry system: • A system of personal identification developed in 1883 • Measurements of the bony parts of the body • Morphological description of the appearance and shape of the body • Description of marks observed on the surface of the body • Bertillon’s system was used until 1903, when it was proven to be unreliable

  5. History of Fingerprinting (2 of 3) • Authorities realized that two people could share identical measurements and facial features, but had unique fingerprints. • The first practical use of fingerprints (1858) occurred with illiterate Indians to prevent forgery on legal documents.

  6. History of Fingerprinting (3 of 3) • Sir Francis Galton developed the first classification system for fingerprints. • 1901: first U.S. use of Galton system (by New York City Civil Service Commission) • 1903: Galton system implemented at New York State Prison System and at Leavenworth Penitentiary • After 1903: Galton system used by police departments in major cities • 1924: records of FBI and Leavenworth Penitentiary merged and moved to Washington, D.C.

  7. Characteristics of Fingerprints (1 of 8) • Fingerprints are unique to a particular individual. • No two fingerprints have the exact same set of characteristics. • Fingerprints do not change over a person’s lifetime or with superficial injury. • Fingerprint patterns can be classified. • Fingerprints do not provide proof of genetic history or racial background. • It is not possible to change one’s fingerprints, although some have tried.

  8. Characteristics of Fingerprints(2 of 8) • U.S. courts rely on a certified fingerprint expert to establish that two prints came from the same individual. • United States v. Bryon Mitchell (1999): • U.S. District Court upheld the admissibility of fingerprint evidence • Fingerprints ruled admissible under Rule 702 and under Daubert v. Merrell Dow Pharmaceuticals

  9. Characteristics of Fingerprints(3 of 8) • Friction ridges do not run evenly across fingertips, but rather form identification point minutiae that can be easily categorized. • Pores on friction ridges emit perspiration that may leave fingerprints behind that are not visible.

  10. Characteristics of Fingerprints(4 of 8) • Fingerprint patterns • Delta: two lines diverge and form a triangle • Arch: lack of any deltas • Loop: only one delta • Whorl: two or more deltas

  11. Characteristics of Fingerprints(5 of 8) • Fingerprint pattern distribution in the general population • 65% are loops • 35% are whorls • 5% are arches

  12. Characteristics of Fingerprints(6 of 8) • Loops: friction ridges enter from one side of the print, curve around, and then exit the same side they entered • Ulnar loop (left hand): enters and exits from the left • Radial loop (right hand): enters and exits from the right

  13. Characteristics of Fingerprints(7 of 8) • Whorls: inner area of the pattern consists of one or more ridges that make a complete circuit between two deltas • Plain whorl: examiner draws a line between two deltas and the line touches the ridge lines • Central pocket loop: ridge lines are not touched • Double-loop whorl: two separate and distinct loop formations • Accidental whorl: more than two deltas

  14. Characteristics of Fingerprints(8 of 8) • Arches: no deltas and no significant core • Tented arch: ridge lines rise and fall rapidly

  15. Fingerprint Identification Points • A single fingerprint may contain as many as 100 or more minutiae that can be used for identification purposes. • Debate continues over how many details must be the same to declare two fingerprints a match.

  16. Methods for Developing Fingerprints (1 of 10) • Latent fingerprint: not readily visible to the naked eye • Patent fingerprint: visible to the naked eye • Plastic fingerprint: impression left on the surface of a soft material such as clay, tar, or wet paint

  17. Methods for Developing Fingerprints (2 of 10) • Finding latent prints requires the use of differing techniques to help visualize the print. • Powders are used when the surface is smooth. • Chemicals are used for soft and porous surfaces.

  18. Methods for Developing Fingerprints (3 of 10) • Recovery from hard surfaces • Black powder: applied to white or light-colored surfaces • Gray powder: applied to dark-colored surfaces, mirrors, and polished metal surfaces • Fluorescent powder: fluoresces when viewed under ultraviolet light • Carbon/charcoal and aluminum powders: applied with a fiberglass or camel’s hair brush • Magnetic-sensitive powders: spread with a Magna Brush

  19. Methods for Developing Fingerprints (4 of 10) • Recovery from hard surfaces • After dusting, the print should be photographed and lifted from the surface. • A hinge lifter includes an adhesive sheet for lifting the fingerprint, plus a backing sheet to seal and protect the fingerprint.

  20. Methods for Developing Fingerprints (5 of 10) • Small particle reagent (SPR) • Consists of finely ground particles suspended in a detergent solution • Used to recover fingerprints on oily or wax-covered surfaces

  21. Methods for Developing Fingerprints (6 of 10) • Recovery from soft surfaces • Iodine fuming • Ninhydrin • Silver nitrate • Super Glue fuming

  22. Methods for Developing Fingerprints (7 of 10) • Iodine fuming • Object is placed in an enclosed chamber with iodine crystals • Temperature is increased until iodine sublimes • Iodine vapors react with body oils and make print visible • Print must be photographed immediately • Print can be sprayed with 1% solution of starch in water to turn the print blue and make it last longer

  23. Methods for Developing Fingerprints (8 of 10) • Ninhydrin • 0.6% solution of ninhydrin powder is dissolved in acetone or ethyl alcohol and sprayed onto the surface • Prints appear in an hour or two • Reaction can be accelerated if the object is heated to 80–100 °C • Reaction of ninhydrin with amino acid from perspiration forms a purple-blue product called Ruhemann’s purple

  24. Methods for Developing Fingerprints (9 of 10) • Silver nitrate • Used after trying iodine fuming and ninhydrin • 3% solution of silver nitrate is brushed onto suspected object • When object is exposed to ultraviolet light, the print turns reddish brown or black

  25. Methods for Developing Fingerprints (10 of 10) • Super Glue fuming • Suspect material and super glue fumes react up to 6 hours in enclosed chamber • In automobiles, a wand can be used to direct fumes to the area of interest

  26. Preservation of Fingerprints (1 of 3) • Objects thought to hold latent prints should be carefully collected and submitted to the lab. • The investigator may have to develop prints at the scene if removal of the object is not possible. • Developed prints must be carefully photographed.

  27. Preservation of Fingerprints (2 of 3) • Photography of fingerprints • Still photography exploits the selective absorption of light by different colors on the surface of the object. • A clearly visible fingerprint can be photographed with a white light source (e.g., a tungsten light bulb). • Use an excitation filter in front of a white light source for a colored print on a colored surface. • Use a filter that is opposite in color to the color of the fingerprint, but close in color to the background substrate.

  28. Preservation of Fingerprints (3 of 3) • Digital imaging of fingerprints • Digital imaging’s higher resolution translates into more detail. • Most digital cameras use a charge-coupled device to produce high-quality images. • The fast Fourier transform (FFT) computer program can convert the digital image and eliminate background noise. • FFT is useful in developing a single print from a object containing multiple, overlapping prints.

  29. Classification of Fingerprints (1 of 2) • The Henry Classification System was Sir Edward Henry. • It was adopted by Scotland Yard in 1901. • It is still in use today. • The Henry system converts forensic ridge patterns in all 10 fingers into two numbers that are arranged as a fraction.

  30. Classification of Fingerprints(2 of 2) • Henry system: assigns a number to each finger • Right thumb = 1 • Left little finger = 10 • Fingers with a whorl pattern = a numerical value • Fingers with a non-whorl pattern = 0 • Primary classification: (1 + sum of the values of the whorl-patterned even-number fingers)  (1 + sum of the values of the whorl-patterned, odd-numbered fingers)

  31. Automated Fingerprint Identification System (1 of 2) • AFIS classifies fingerprints based on the distance between the core and delta, minutiae locations, and pattern type • The FBI released the Integrated AFIS in 1999 • Most modern AFIS systems compare fingerprint minutiae • The systems concentrate on points where forensic ridge lines end or where one ridge splits into two (bifurcation)

  32. Automated Fingerprint Identification System (2 of 2) • Having the same number of minutiae is not enough to declare a match; individual minutiae must also be located at the same place on each print. • The scanner system identifies matching minutiae patterns. • The exact number of matches needed for positive identification depends on the country; there is no set number for the United States or United Kingdom.

  33. Fingerprints for Biometric Identification (1 of 3) • Biometrics entails the authentication of the identity of an individual using fingerprints, palm prints, retinal scans, or other biological signatures. • The computer compares the applicant to a relatively small number of possibilities in its database of authorized users.

  34. Fingerprints for Biometric Identification (2 of 3) • Finger scanning • Most departments currently use optical finger scanners for scanning fingerprints. • Scanners can be adjusted to alter the exposure, reposition fingers, and assure clarity of scans. • A computer algorithm identifies minutiae points on the scanned print and locates them relative to other points on the print.

  35. Fingerprints for Biometric Identification (3 of 3) • Biometrics-related issues • If your fingerprints fall into the hands of a criminal, you could have serious problems for the rest of your life. • The Enhanced Border Security and Visa Entry Reform Act of 2002 mandated use of biometrics for issuance of a U.S. visa.

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