first systematic attempt at personal fingerprints · detection of prints •latent prints must be...
TRANSCRIPT
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Fingerprints
Chapter 14
Criminalistics
History of Fingerprinting
– First systematic attempt at personal identification • Alphonse Bertillon in 1883
– Anthropometry: system of precise body measurements
• Included detailed descriptions of the subject
• Full-length and profile photographs • Accuracy of measurements were disproved
by the William West Case
History of Fingerprinting
• Francis Galton – 1892: Published Finger Prints
• Described the anatomy of fingerprints and suggested methods for recording them
• Acknowledged that no two prints are alike and do not change throughout a lifetime
• Three pattern types
– Loops, Arches, and Whorls
Fundamental Principles of Fingerprints
• First Principle – A fingerprint is an individual characteristic. No
two fingers have yet been found to possess identical ridge characteristics
– Individuality of a fingerprint is not determined by its general shape or pattern but by careful study of ridge characteristics or minutiae
• Examples: bifurcation, enclosures, islands, ridge endings, short ridges, ridge crossings, deltas
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Figure 14-1 Figure 14-2
Fundamental Principles of Fingerprints
• Second Principle – Fingerprints have been designed by nature to
increase grasp and to resist slippage and are formed in the fetal stage of development.
– Fingerprints are formed by: • Hills (Ridges): raised portions of the
epidermis • Valleys (Grooves): lowered portions of the
epidermis • IT IS THE RIDGES THAT ARE INKED
WHEN FINGERPRINTS ARE TAKEN
How are Fingerprints Formed?
• The Dermal Papillae is the boundary between the epidermis (outer skin) and the dermis (inner skin).
• The shape of this boundary is wavy. This wave pattern determines the pattern of the fingerprint and remains unchanged throughout your lifetime.
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Leaving Your Mark • Skin ridges have a single row of pores
that open from the sweat glands. • Perspiration is discharged through
the pores and oils from the body collect in the ridges and valleys.
• Impressions from the fingertips are transferred onto a surface, leaving a fingerprint. – Latent fingerprints are deposited in this
manner and cannot be seen with the naked eye.
Fundamental Principles of Fingerprints
• Third Principle
– Fingerprints have general ridge patterns that permit them to systematically classified.
Taking Fingerprints • Fingers are rolled in ink left-to-right,
careful not to adhere too much ink to the fingertips
• The fingertips are then rolled left-to-right on a Ten-Print Card in the appropriate place for each finger
• A straight down print is then taken for each of the four fingers simultaneously and for each thumb and recorded on the Ten-Print Card
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This is the original Ten-Print Card
of Rosa Parks after
the Montgomery Bus Boycott
Three Classes of Fingerprints
• Loops, Whorls, and Arches
– Loops: 65% of world’s population
– Whorls: 30-35% of world’s population
– Arches: 5% of world’s population
Loop Patterns
• One or more ridges entering from one side of the print, recurving, and exiting from the same side
Types of Loop Patterns • Ulnar Loop: loop opens toward little
finger
• Radial Loop: loop opens toward the thumb – Type Lines: pattern area of the loop
surrounded by two diverging ridges
– Delta: the point directly in front of the diverging ridges—loops MUST have at least one delta
– Core: the center of pattern
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Types of Whorl Patterns
• Four types of patterns – Plain Whorl
– Central Pocket Loop Whorl
– Double Loop Whorl
– Accidental Whorl
All whorl patterns must have type lines and a MINIMUM of two deltas.
Types of Whorl Patterns
• Plain and Central Pocket Loops
– Plain whorl and central pocket loops have AT LEAST one ridge that makes a complete circuit
– Ridge may be a spiral, oval, or any variant of a circle
Types of Whorl Patterns
• Plain Whorl: an imaginary line is drawn between TWO deltas and the spiral is crossed
• Central Pocket Loop: spiral is not crossed when imaginary line is drawn
Types of Whorl Patterns
• Double Loop: has two loops in one fingerprint
• Accidental Loop: has two or more patterns or is not classified into any other category
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Types of Whorl Patterns
Figure 14-6
Arch Patterns
• Plain arch: ridges entering one side of the fingerprint and exiting the other side
• Tented arch: this pattern rises sharply in the center
Arch Patterns
Figure 14-7
Classification of Fingerprints
• Original System: Henry System – Developed by Scotland Yard in 1901 – Converted ridge patterns on all 10
fingers into a series of letters and numbers arranged into a fraction
– Problem: could only classify fingerprints up to 100,000 files
– Evolved into the FBI System of Fingerprint Classification
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FBI System
• Primary System of Classification based on the Henry System
• All fingerprints in the world can be classified into 1,024 groups
How the FBI System Works • Fingers are given numbers based on whorl
patterns being present on each finger
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 0 Whorl Values
Zeros are assigned for loops and arches
Fraction gives individualized result for each person
+ + + + +
Problems with FBI System
• 25% of population falls into the 1/1 category
• Only useful when all 10 prints are available
• Cumbersome and Time Consuming to look through cards
• Often only one or two prints found at a crime scene
AFIS
• Automated Fingerprint Identification System
• Computer-scans and digitally encodes fingerprints based on minutiae of ridge endings and bifurications
• List of prints is generated then a fingerprint examiner confirms match
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Benefits of AFIS
• Computer can make thousands of accurate fingerprint comparisons in a second
• Can filter out imperfections in latent prints found at a crime scene
• Suspect lists are generated faster and investigators can spend more time focusing on suspects
A Typical AFIS Matching Screen
Types of Crime Scene Prints
• Three Types: – Visible Prints
– Plastic Prints
– Latent (Invisible) Prints
Visible Prints
• Can be seen with the naked eye
• Made by fingers touching a surface after ridges have been in contact with a colored material such as blood, paint, grease, ink, etc.
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Plastic Prints
• Can be seen with the naked eye
• Made by ridge impressions left on a soft material such as putty, wax, soap, dust, wet paint surfaces, etc.
Latent Prints
• Cannot be seen with the naked eye
• Made by impressions caused by transfer of body perspiration or oils present on finger ridges to the surface of an object
Detection of Prints
• Latent prints must be developed (found) through different methods
• The method used is dependent on the surface being examined
Surface Conditions
• Hard, nonabsorbent surfaces (glass, mirrors, tile, painted wood): Powders or SuperGlue Fuming
• Absorbent surfaces (paper, cardboard, cloth): One or more specific chemicals
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Fingerprint Powders • Non-absorbent surfaces only • Applied with a camel’s hair or fiberglass
brush • Color of powder chosen contrasts with
surface color • Powder adheres to oils and perspiration
left by ridges • Print can be lifted off the surface and
preserved
Iodine Fuming
• Oldest chemical method for developing latent prints
• Iodine is a solid crystal that, when heated, is transformed into a gas through sublimation
• Material is placed in a chamber and iodine is heated and latent prints are revealed
• Iodine prints are not permanent and must be photographed immediately or fixed with starch solution, which can last about 1 month
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Ninhydrin
• Chemical used to develop prints on porous material by reacting with amino acids in perspiration
• Developed prints appear purple-blue in color
• Prints appear within an hour or two and fully developed in 24-48 hours
• Commonly used on paper products
Latent Prints recovered on paper with Ninhydrin
Physical Developer • Silver-nitrate based chemical
• Useful for detecting prints that cannot be found by other methods or on objects that have been wet at one time
• Application of Physical Developer washes away any protein that may be present and MUST be used last
SuperGlue Fuming • Used on nonporous surfaces such as
metal, electrical tape, leather, and plastic bags
• Active ingredient: cyanoacrylate ester
• Evidence is placed in a fuming chamber and the cyanoacrylate is heated and covers the object and produces a white latent print
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Flashlight battery exposed to SuperGlue Fuming
Laser Light
• Perspiration contains a variety of components that fluoresce when illuminated by laser light
• Because of the fluorescence, latent prints can be seen with the naked eye
• Almost never used anymore with the invention of alternate light source latent print examination
Alternate Light Source
• Works because perspiration fluoresces under different wavelengths of light
• Can adjust the wavelength of light to be aimed through a fiber optic cable
• More commercially available than laser light setups
Alternative Light Source being used to detect latent prints
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Preservation of Prints
• Common fingerprint methods do not interfere with further DNA analysis
• However, when biological material remains, fingerprints should be developed at the crime lab instead of at a crime scene
Preservation of Prints
• After prints have been found, photos must be taken
• If object is small enough to be transported without destroying the print, it should be preserved intact
• Cellophane should cover the print to protect from damage
Preservation of Prints
• Prints on immovable objects should be lifted
• Lifted prints should be preserved on a card that provides contrast