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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