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October 29, 2014
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 dermisand 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
October 29, 2014
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)
October 29, 2014
October 29, 2014
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 fingerradial 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
October 29, 2014
October 29, 2014
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 orany 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 acentral pocket loop
October 29, 2014
Line drawn between two deltas touches spiral ridges
Line drawn between two deltas does not touch spiral ridges
October 29, 2014
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 othercategories - may consist of a combination loop and plain whorl or loop and tented arch
October 29, 2014
Arches:- 5% of the population - least common- no type lines, deltas or cores
- plain arches: simplest of all fingerprint patterns - formedby ridges entering from one side of the print and exiting fromthe 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
October 29, 2014
Fundamental Principles of Fingerprints#1: A fingerprint is an Individual Characteristic
- no two fingers have yet been found to possess identicalridge characteristics
- individuality of a fingerprint is determined by a carefulstudy of its ridge characteristics (minutiae)- identity, number and relative location of characteristicsimpart individuality to a print- point-by-point comparison must be demonstrated in courtproceedings
Characteristics:1. Bifurcation2. Enclosure - if enclosure is present, has a bifurcation3. Ending Ridge (has a dead end or a terminal)4. Short Ridge (start and stop --> short - has a terminal)5. Ridge dot
October 29, 2014
October 29, 2014
October 29, 2014
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
October 29, 2014
Classification of Fingerprints: Henry Number SystemPrimary 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 LittleR 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 totaledand 1 is added to numerator and denominator - fraction obtained is primary classification
October 29, 2014
October 29, 2014
Visible vs Plastic vs Latent PrintsVisible 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
October 29, 2014
Detection of Latent Prints- several methods to make latent prints visible - choicedepends 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 aidof chemical or powder treatments
October 29, 2014
Powders:- available in a variety of compositions and colors- used on nonabsorbent (nonporous) surfaces- adhere to perspiration and/or deposits of body oils left onsurface- 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 coloredsurfaces- fluorescent powders: fluoresce under UV light
October 29, 2014
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 oncefuming 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
October 29, 2014
October 29, 2014
Super Glue Fuming:- develops latent prints on nonporous surfaces- exposes prints to cyanoacrylate vapors- fumes and object are placed in an enclosed chamber forup 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 adhesiveside of the tape an pulled up, powder is transferred to thetape- tape is then placed on a labeled card that provides a goodbackground contrast with powder
October 29, 2014
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)
October 29, 2014
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