Unit 2 Notes: Fingerprints

(1) What Is A Fingerprint? Impression left on objects from the ridges on the surface of skin. Composed of oil secretions from skin. Often mixed with different concentrations of water, salt, and dirt. Function to increase grip friction.

(2) Fingerprint Formation: Layers of skin: Epidermis / Basal Dermis  Subcutaneous Skin cells actively divide within the basal layer… This is the first layer in the skin to divide during fetal development. Because basal layer divides and thickens unevenly, and faster than epidermis, it creates bumps/ridges under epidermis.

(3) Fingerprint Characteristics Loops: A turn-around shape (Like a loop of string). Approximately 65% of population. Whorls: Circular-Maze like pattern. Approximately 30% of the population. Arches: Bent line pattern. Approximately 5% of the population.

(4) Core & Delta Structures: Core: The center of a loop or whorl. Delta: A triangular region located near a loop or whorl. Formed by the rising of some ridge patterns, and the falling of others. Forms a noticeable gap in the ridges.

(5) Ridge Count: Example: Procedure: Draw a straight line from CORE  center of DELTA. Count the number of ridges intersecting line. Example:

(6) Whorl Details: Plain Whorl: (24% of population) 1 or more ridges that make a spiral. 2 Deltas. Line between Deltas should intersect central pattern. Central Pocket Loop Whorl: (2% of population) 1 or more ridges that make a complete circle. Line between Deltas does not intersect central pattern. Double Loop Whorl: (4% of population) 2 separate loop formations. Accidental Whorl: (0.01% of population) 2 or more Deltas. Combination of 2 of the other patterns (loop or arch), but not a plain arch.

(7) Arch Details: Plain Arches: (4% of population) Ridges appear to enter one side, and exit the opposite side. Ridges appear to rise in the central pattern. No loop characteristics or patterns. Tented Arches: (1% of population) Central pattern forms a shape similar to a Delta. More pointed central pattern.

(8) Minutiae of Ridge Patterns: Looking at small details, their relative location, and relationship with other details/patterns. 150 total unique ridge patterns found in EACH fingerprint. Common Ridge Patterns: Ending / Broken Ridge  Plain straight lines. Fork Ridge / Bifurcation  Y-shape (like fork in road). Island Ridge / Short Ridge  2 Straight lines with a dash (island) in between. Dot Ridge / Very Short Ridge  2 Straight lines with a small dash (island) in between. Bridge Ridge  2 Straight lines with a dash (bridge) connecting them in between. Spur / Hook Ridge  2 Straight lines with an angled dash (hook) in between them. Eye / Enclosure Ridge  1 Straight line with a bubble in the middle. Double Bifurcation Ridge  1 Straight line that breaks off into several uneven branches/forks. Delta Ridge  Y-shape with a small dot (island) in between fork. Trifurcation Ridge  Like a Y-shape but with 3 prongs instead of 2.

(9) Types of Fingerprints: Patent / Visible Prints: Left on a smooth surface. Usually when blood, ink or some liquid is transferred on the hands to a surface. Plastic Prints: Actual Imprint left in a material. Materials are usually softer like clay, putty, wax, sand, mud. Latent Prints: Hidden prints Caused by the transfer of oils and other body secretions. Usually visible when mixed with a dry powder or a chemical reaction which reveals the patterns.

(10) Collecting Fingerprints: Each finger rolled in ink and then rolled onto a ten card. A ten card is the data sheet used to organize each finger. Collecting Latent Prints: (Application of…) Metal / Magnetic Powder Dust on powder Dust adheres to surface of ridge patterns Lift with tape Ninhydrin  Used for paper surfaces Spray or dip surface in chemical Reacts with amino acids in sweat Leaves a purple-blue print Cyanoacrylate Vapor  Used for plastics, metals, glass, skin Enclose surface in a heated chemical tent. Reacts with amino acids adhering to ridges. Leaves a white print. Silver Nitrate  Used for wood or styrofoam Salt in sweat combines with silver nitrate to form silver chloride. Leaves a black/red-brown print under UV light. Iodine Fuming  Used for cardboard and unpainted surfaces Iodine reacts with carbohydrates in ridges. Leaves a brown print which can be photographed.

(11) Fingerprint Analysis: Most analysis is NOT done by computers, but by people. People have to manually analyze fingerprints collected, 1 at a time. People have to them manually search the database 1 print at a time for comparison. Usually takes 3-6months to find a match. AFIS (Automated Fingerprint Identification): People still have to manually analyze fingerprints collected. Takes 2-24hours to find matches. People then have to manually compare matches. Most offices do NOT have full access to AFIS.