Fingerprints - Formation - Fingerprints are a reproduction of friction skin ridges that are on the palm side of fingers and thumbs - these skin surfaces have been designed by nature to provide our bodies with a firmer grasp and resistance to slippage - composed of a series of lines corresponding to hills (ridges) and valleys (grooves) - skin is composed of a layer of cells - epidermis: outer portion of skin - dermis: inner skin - dermal papillae: boundary of cells separating the dermis and epidermis - shape of this boundary determines the form and pattern of ridges on the surface of the skin - fingerprints are formed in the fetus and remain unchanged
Fingerprints - Formation (cont) - each skin ridge has a single row of pores that are the openings of ducts for sweat glands and deposit perspiration on the skin - when a finger touches a surface, perspiration and oils are transferred to the surface leaving an impression of the finger's ridge pattern (or fingerprint)
Types of Fingerprints - all fingerprints are divided into 3 classes based on their general pattern: loops, whorls, and arches Loops: - 60-65% of population have loops - must have one or more ridges entering from one side of the print, recurving, and exiting from the same side ulnar loop: loop opens toward the little finger radial loop: loop opens toward the thumb type lines: pattern area of loop is surrounded by diverging ridges delta: ridge point at or nearest the divergence core: approximate center of the pattern
Whorls: - 30-35% of the population - divided into four distinct groups: plain, central pocket loop, double loop and accidental - all whorls must have type lines and at least two deltas - plain whorls and central pocket loop have at least one ridge that makes a complete circuit (may be spiral, oval or any variation of a circle) - if an imaginary line drawn between the two deltas within these two patterns touches any one of the spiral ridges, the pattern is a plain whorl - no ridge touched it is a central pocket loop
Line drawn between two deltas touches spiral ridges Line drawn between two deltas does not touch spiral ridges
Whorls (cont): - double loop is made of two loops combined into one fingerprint - classified as a whorl bc there is no core as is required by a loop classification - accidental either contains two or more patterns (not including plain arch) or is a pattern not covered by other categories - may consist of a combination loop and plain whorl or loop and tented arch
Arches: - 5% of the population - least common - no type lines, deltas or cores - plain arches: simplest of all fingerprint patterns - formed by ridges entering from one side of the print and exiting from the other side - ridges tend to rise in the center of the pattern - tented arches: like a plain arch, but instead of rising smoothly at the center, there is a sharp upthrust or spike
Fundamental Principles of Fingerprints #1: A fingerprint is an Individual Characteristic - no two fingers have yet been found to possess identical ridge characteristics - individuality of a fingerprint is determined by a careful study of its ridge characteristics (minutiae) - identity, number and relative location of characteristics impart individuality to a print - point-by-point comparison must be demonstrated in court proceedings Characteristics: 1. Bifurcation 2. Enclosure - if enclosure is present, has a bifurcation 3. Ending Ridge (has a dead end or a terminal) 4. Short Ridge (start and stop --> short - has a terminal) 5. Ridge dot
Fundamental Principles of Fingerprints(cont.) #2: A fingerprint remains unchanged during and individual's lifetime - formed as a fetus and do not change, only grow larger - must cut 1-2mm deep into fingerprint to get a scar #3: Fingerprints have general ridge patterns that permit them to be systematically classified - can classify prints into loops, whorls or arches
Classification of Fingerprints: Henry Number System Primary Classification: (purpose is to provide print examiner with a number of candidates) - first step is to pair up fingers, placing one finger in the numerator of the fraction the other in the denominator: R Index R. Ring L. Thumb L Middle L Little R Thumb R Middle R Little L Index L Ring - presence or absence of a whorl is basis for determining primary classification - if a whorl is present on any finger in the first pair, it is assigned a value of 16; second pair 8; third pair 4; fourth pair 2; and last pair 1 - any finger with arch or loop is given a 0 - after values for all ten fingers are obtained, they are totaled and 1 is added to numerator and denominator - fraction obtained is primary classification
Visible vs Plastic vs Latent Prints Visible Prints: made by fingers touching a surface after the ridges have been in contact with a colored material such as blood, paint, grease or ink Plastic Prints: ridge impressions left on a soft material such as putty, wax, soap or dust Latent (invisible) Prints: impressions caused by the transfer of body perspiration or oils present on finger ridges to the surface of an object
Detection of Latent Prints - several methods to make latent prints visible - choice depends on surface being examined (porous vs nonporous) - porous surfaces (paper, cardboard, cloth) generally require treatment with chemicals - nonporous surfaces (glass, mirror, tile, painted wood) generally work with the application of powder or treatment with Super Glue - RUVIS (reflected UV imaging system): a device that can locate prints on most nonabsorbent surfaces without the aid of chemical or powder treatments
Powders: - available in a variety of compositions and colors - used on nonabsorbent (nonporous) surfaces - adhere to perspiration and/or deposits of body oils left on surface - examiner picks the powder with the best color contrast with the surface being dusted Powder Types: - gray powder: aluminum dust; dark-colored surfaces, mirrors, metal surfaces - black powder: carbon or charcoal; white or light colored surfaces - fluorescent powders: fluoresce under UV light
October 29, 2014
Iodine Fuming: - makes latent fingerprints appear by exposing them to iodine vapors - suspect material is placed in an enclosed cabinet with iodine crystals and as iodine is heated vapors fill cabinet and make print visible - iodine prints are not permanent and begin to fade once fuming process is stopped - must photograph immediately Ninhydrin: - a chemical that reacts with amino acids in perspiration - creates a blue-purple color - used on porous surfaces - prints appear within an hour or two after application - can speed up by placing in an oven
Super Glue Fuming: - develops latent prints on nonporous surfaces - exposes prints to cyanoacrylate vapors - fumes and object are placed in an enclosed chamber for up to 6 hours - fumes from the glue adhere to the print, producing a white-appearing latent print October 29, 2014
Preservation of Developed Prints - once latent print has been visualized, it must be permanently preserved - prints are usually photographed - prints developed with powder can be "lifted" - involves adhesive tape similar to clear tape - when the powdered surface is covered with the adhesive side of the tape an pulled up, powder is transferred to the tape - tape is then placed on a labeled card that provides a good background contrast with powder
AFIS (Automated Fingerprint Identification Systems) - FBI has a system that links state AFIS computers with FBI database - FBI database has approx 50 million fingerprint records - AFIS uses automatic scanning devices that convert the image of a fingerprint into digital minutiae that contain data showing ridges at their points of termination (ridge endings) and the branching of ridges into two ridges (bifurcations)