6. Fingerprints

6. Fingerprints Fingerprints Historical Facts • 1883: Alphonse Bertillon: Anthropometry • Chinese used to sign legal documents • Indians used to sign contracts • 1880: Henry Fauld: Ridge patterns could be used for identification • 1901: Sir Edward Richard Henry (1897): Henry system of classification General Facts • Minutiae: Ridge characteristics • Point by point comparison (8-16 points) • 150 individual characteristics on each finger (average) • 1973 International Association for Identification: No predetermined number of points required Essential Principles 1. Formed during fetal life; remain unchanged Types Latent, Visible, Plastic 7. Fingerprints are unique 8. Can be classified systematically • Pattern of friction ridges • Present on fingers, palms, toes Patterns • Loop (1 Delta): Ulnar, Radial Different Fingerprint Patterns (Deltas Are Circled) • Whorl (2 Deltas): Plain, Central Pocket Loop, Double Loop, Accidental • Arch (0 Deltas): Plain, Tented Latent Fingerprint Locating Tools Components • Water, Salts, Oils, Amino Acids Powders, Chemicals, Alternate Light Sources, Oblique Lighting Ideal Surface • Hard, Smooth, Non-Porous (e.g. Glass) Latent Print Locations • Walls, Tables, Windows, Cars, Tools, TV Remote, Guns, Knives, Destroyed Material, Items at Scene, Cell Phones, Bathrooms Latent Fingerprints on a Glass Shown by ALS Chemical Methods (Absorbent Surfaces) Iodine Fuming • Oldest Chemical Method • Iodine: Solid Crystal; Sublimates • Combines with Fatty Oils • Possibly Combines with Residual Water Iodine Fumed Print • Rust Color • Fades Over Time Li/d2d781ca7b284a165f943de696610f5491e69015/figure/9"htt Ninhydrin • Forms Purple-Blue Color • Reacts with Amino Acids • Sprayed onto Porous Surfaces • Usually Mixed with Acetone • Prints Appear Within 1-2 Hours • Heat Speeds up Reaction • Can Locate Prints up to 15 Years old Silver Nitrate Print Ninhydrin Print Silver Nitrate • Reacts with Salts • Chloride Ion; Forms Silver Chloride • Prints Develop by Exposure to UV Light • Prints turn Brown Cyanoacrylate (Super Glue Fuming) • Workers at Super Glue Factory found white fingerprints on the walls of the factory • When heated it vaporizes; vapors adhere to fatty oils Super Glue Fumed Prints • Prints are white and permanent Lasers & Alternate Light Sources • Cause objects to fluoresce when illuminated by lasers and viewed through barrier filters. • Many times fluoresces off of perspiration. • Prints can also be treated with chemicals to help them fluoresce. • Quartz, Xenon monochromatic light sources. • Portable Adermatoglyphia Rare genetic disorder where people are Chemicals born without fingerprints. • Leuco Crystal Violet (LCV): Blood • Crystal Violet: Blood • Amido Black: Blood • Adhesive Side Developer: Tape • Small Particle Reagent: Glass The Fingers of a Person with Adermatoglyphia Scientific Reliability of Fingerprints • Fingerprint examiners have not adopted a single standard for determining when a fragmentary latent fingerprint is sufficient to permit a comparison. • Unique nature of fingerprints is counterintuitive to the establishment of such a standard. • Through experience, each examiner develops a comfort level for deciding how much of a fragmentary print is necessary for comparison. AFIS: Automatic Fingerprint Identification System • Images are scanned and marked by a technician. • Computer makes matches based on where points are plotted. • Can do in 20 minutes what one detective looking at 1.7 million print cards would need 67 years. • Look at a full set or individual prints. • Creates digitally recorded geometric patterns (like a graph). ACE-V Analysis • Condition of Skin, Type of Residue, Mechanics of Touch, Nature of Surface Touched, Development Technique, Capture Technique, Size of Latent Print, % of Surface Available. • If the latent print does not have sufficient detail for either identification or exclusion, it does not undergo the remainder of the process and ends the examination. Comparison • Discerning, visually measuring and comparing the details that correspond. • Shape, Anatomical Aspects, Ridge Flows and Counts, Core, Delta Location, Scars etc. Evaluation • Point by Point • The agreement of the friction ridge formations in the two prints. • The sufficiency of the detail present to establish an identification. Verification • Another qualified examiner repeats the observations and comes to the same conclusion. • Confirmation Bias: Tendency to seek confirming rather than disconfirming evidence Reporting of Results • SWGFAST: 3 acceptable conclusions resulting from latent print comparison. • Individualization: Latent was left by the same ‘person of interest’ who provided the known. • Exclusion: Latent was left by another person other than the ‘person of interest.’ • Inconclusive: Insufficient information in the latent or known print (or both) to conclude as to the source of the latent. ACE-V does not specify particular measurements or a standard test protocol, and examiners must make subjective assessments. Classification of Fingerprints • Henry system: Scotland Yard 1901 • Converts ridge patterns on all 10 fingers into a series of numbers to form a fraction. • Can only accommodate 10,000 files. • FBI System Primary Classification • Part of the original Henry System. • First step in the FBI System. • Using this classification alone, all fingerprint cards in the world could be divided into 1024 groups. • R. Index + R. Ring + L. Thumb + L. Middle + L. Little + 1 • R. Thumb + R. Middle + R. Little + L. Index + L. Ring + 1 • 16 + 8 + 4 + 2 + 1 + 1 • 16 + 8 + 4 + 2 + 1 + 1 • Only Whorles Get Points Ridge Characteristics 1. Ridge Endings: When a ride suddenly stops between 2 other ridges. • AFIS automatically flags ridge endings. 2. Bifurcation: A split in the ridge (like Y) 3. Short Ridge: Short friction ridge with 2 ends between 2 other friction ridges. 4. Enclosure: 2 Bifurcations back to back. • Usually found towards the center of print. 5. Island: A dot between 2 ridges. 5. Ridge Crossing: 2 ridges cross over each other (like X).