Fingerprints

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PRENTICE HALL ©2007 Pearson Education, Inc. Upper Saddle River, NJ 07458

CRIMINALISTICS An Introduction to Forensic Science, 9/EBy Richard Saferstein 1

Chapter 14Fingerprints

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History• Alphonse Bertillion

– French police expert– First systematic attempt at personal

identification was• Bertillion system

– Relied on a detailed description of the subject

– Combined with full length and profile photographs

– System of precise body measurements called anthropometry

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History

• Francis Galton– 1892– Classic textbook finger prints

• At Galton’s insistence– British government adopted fingerprinting– Supplement to the bertillion system.

• Next step– Creation of classification systems– Capable of filing many thousands of prints– Logical and searchable sequence.

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History• Dr Juan Vucetich

– Devised a classification system– Still used in most spanish-speaking countries

• Sir Edward Henry: system used in most English-speaking countries.

• Will West and William West case– 1903– Bertillion system could not distinguish between

men– Fingerprinting that clearly distinguished them

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History• Fingerprinting used by the New

York city civil service commission in 1901

• Training of American police by Scotland yard representatives at the 1904 world’s fair

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Fingerprint Principles

Reproduction of friction skin ridges Palm side of the fingers

& thumbs

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Fingerprint Principles• Individual characteristic

– Because no two fingers with with identical ridge characteristics

• Remains unchanged during an individual’s lifetime

• General ridge patterns that permit systematic classification

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Principle One

Individual CharacteristicNo Fingers Identical

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Principle One• Mathematical probability for

existence of two identical fingerprint patterns in the world’s population = almost zero

• Millions upon millions of individuals who have had their prints classified–No two fingerprints have been

found to be identical

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Figure 14–1 Fingerprint ridge characteristics. Courtesy Sirchie Finger Print Laboratories, Inc., Youngsville, N.C., www.sirchie.com.

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Principle One• Individuality of fingerprint not

determined by its general shape or pattern

• Careful study of its ridge characteristics, known as minutiae.– Identity, number, and relative

location – Individuality to a fingerprint.

• As many as 150 minutiae on the average finger

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Principle One• Three year study

– “No valid basis exists for requiring a predetermined minimum number of friction ridge characters which must be present in two impressions in order to establish positive identification”

• Judicial proceeding– Expert must demonstrate a point-

by-point comparison– To prove the identity of an

individual

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Figure 14–2 A fingerprint exhibit illustrating the matching ridge characteristics between the crime-scene print and an inked impression of one of the suspect’s fingers. Courtesy New Jersey State Police.

Fingerprint Comparison

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Principal Two

Remains Unchanged During Lifetime

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Principal Two• Epidermis

– Outer layer of the skin

• Dermis– Inner layer of the

skin

• Dermal papillae– Layer of cells

between the epidermis and dermis

– Responsible for determining the form and pattern of the ridges on the surface of the skin

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Principal Two• Dermal papillae

develop in the human fetus

• Ridge patterns will remain unchanged throughout life

• Enlarge during growth

• Fingerprint remains unchanged during lifetime

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Principle Two• Skin ridge is

populated with pores leading to sweat glands

• Perspiration is deposited on the skin

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Principle Two•Finger touches a surface–Perspiration–Oils from hairy portions of the body

–Transferred onto surface•Leaves fingerprint

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Principle Three

Ridge Patterns Permit Systematic Classification

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Principle Three•All fingerprints– divided into three classes – Loops–Arches–whorls – L.A.W.

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Loop Patterns

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Principle Three - Loops• A loop must have one or more

ridges entering from one side of the print, recurving, and exiting from the same side.– If the loop opens toward the

little finger, it is called an ulnar loop.

– If the loop opens toward the thumb, it is called a radial loop.

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Figure 14–5 Loop pattern.

Principle Three - Loops

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Principle Three - Loops• Must have one

delta• Ridge point at or

directly in front of the point where two ridge lines (type lines) diverge

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Whorls

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Principle Three- Whorls• Divided into four groups–Plain–Central pocket loop–Double loop–Accidental

• All have type lines and minimum of two deltas

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Whorls• Plain whorl and central pocket loop have at

least one ridge that makes a complete circuit• Double loop: two loops combined into one

fingerprint• Accidental

– Two or more patterns– Or pattern not covered by the other categories

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Plain Whorls• More than 1 valid delta • If you look at image A you should be

able to identify the two delta's. If not then look at image B and you will see that they are displayed in the red boxes.

• Whorl: one or more ridges which make complete circuit

• Two delta's– Between which an imaginary line is

drawn– At least one recurving ridge within the

inner pattern area cut or touched.

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Plain Whorls

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Whorls• Inner area of the pattern forms

circle or oval• Specific ridges that are making

or trying to make the circle– Imaginary line between the

two delta's (the red line in image)

–No lines that form the circle are intersected

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Whorls

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Arches

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Principle Three - Arches• Least common of

general patterns–Plain arches–Tented arches

• No lines that form the circle are intersected

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Plain Arches• Ridges entering from one side of

the print• Rising and falling• Exiting on the opposite side• Like a wave

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Tented Arches• Sharp upthrust

or spike• The ridges meet

at an angle that is less than 90 degrees

• Arches do not have type lines, deltas, or cores

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Primary Classification• Based on knowledge of

fingerprint pattern classes• Fingers are paired up–One finger in the numerator of

a fraction–Other in the denominator

• Presence or absence of the whorl pattern–Basis for the determination of

the primary classification

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Primary Classification• Whorl pattern

– Any finger of the first pair value = 16

– On the second pair value = 8– On the third pair value = 4– On the second pair value = 2– On the last pair value = 1

• Any finger having a loop or arch value = 0

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Primary Classification• Values for all 10 fingers totaled• 1 is added to both the numerator

and denominator• Fraction obtained is primary

classification.

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Primary Classification• 25 percent of the population

– 1/1 category– All fingers loops or arches

• Cannot in itself unequivocally identify an individual

• Provides the fingerprint examiner with a number of candidates

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AFIS

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AFIS• Computer to scans, digitally

encodes fingerprints• Can be high-speed computer

processed

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AFIS• AFIS aids in classifying and

retrieving fingerprints–Converts image of a fingerprint

into digital minutiae –Contain data showing ridges at

their points of termination (ridge endings) and their branching into two ridges (bifurcations).

• Thousands of comparisons per second

• Produces a list of file prints to be examined by a trained fingerprint expert

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Visible & Latent Prints

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Latent Prints• Invisible fingerprints• Finger touches a surface• Body perspiration and/or oils

present• Transferred to that surface• Leaves impression• Invisible to the eye

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Visible Prints• Fingers touch a surface after contact

with a colored material such as blood, paint, grease, or ink

• Plastic prints: left on a soft material, such as putty, wax, soap, or dust

• Little problem to the investigator• Usually distinct and visible to the eye.

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Detecting Prints

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Detecting Prints• Hard nonabsorbent surfaces–Glass, mirror, tile, painted

wood–Developed by the application

of a powder• Porous surfaces–Papers, cardboard, and cloth–Require treatment with a

chemical

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Ninhydrin• Reacts chemically with trace

amounts of amino acids• Produces a purple-blue color• Messy and stains skin badly

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Physical Developer• Silver nitrate-based reagent• Used when other chemical

methods are ineffective• Silver nitrate solution stain

skin

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Super Glue®

• Nonporous surfaces –Metals, electrical tape, leather,

plastic bags –Fumes from the glue adhere to

the print–Produce white latent print

• 98 to 99 percent cyanoacrylate ester

• Super Glue fuming– Fuming chamber (for up to six hours)– Handheld wand that heats a small

cartridge containing cyanoacrylate

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Reflected UV Imaging System

•RUlVIS•No chemicals or powder•Locate With light source• investigator develops the

print in the most appropriate fashion

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Figure 14–17 Schematic depicting latent-print detection with the aid of a laser. A fingerprint examiner, wearing safety goggles containing optical filters, examines the specimen being exposed to the laser light. The filter absorbs the laser light and permits the wavelengths at which latent-print residues fluoresce to pass through to the eyes of the wearer. Courtesy Federal Bureau of Investigation, Washington, D.C.

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Powders•Powders, available in a

variety of colors, can be applied with a brush or magnetic wand, and adhere to perspiration and/or body oils of the print.

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Iodine Fuming• Molecular iodine solid at room

temperature• Heat iodine crystals• Iodine vapors • Combine with latent prints to

make them visible– Iodine prints are not permanent– Will fade– Must photograph the prints

immediately

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Fluorescence• High sensitivity• New chemical techniques used to

visualize latent fingerprints• Fingerprints treated with

chemicals – Induce fluorescence when

exposed to lasers–High-intensity light sources

(“alternate light sources”)–Quartz halogen, xenon arc, or

indium arc light sources.

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Preservation of Prints•Visualized latent print•Permanently preserved–Future comparison–Possible use as court

evidence

•Photograph must be taken–Before any attempts at

preservation

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Transporting Prints• small object: preserve in its

entirety. • large immovable objects

– developed with a powder– “lift” with a broad adhesive tape.– tape placed on properly labeled

card– good background contrast with the

powder

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Digital Imaging• Picture converted into digital

computer file• Help of digital imaging software–Enhanced for the most

accurate and comprehensive analysis

• Compare function–Two images side by side–Allows the examiner to chart

the common features on both images simultaneously

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Fingerprint Patterns

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Taking Fingerprints

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SummarySummary

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Fingerprints

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