chapter 4: fingerprints

Chapter 4: Fingerprints

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History• First fingerprints were discovered in

clay pottery during the T’ang Dynasty

• Dactyloscopy: study of fingerprints

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History• Alphonse Bertillion

– First systematic attempt at personal identification

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.

WHY FINGERPRINTS?• The most positive means for

identifying people.

• Because no two fingers with identical ridge characteristics

• Fingerprints form on a person before birth and remain unchanged until the body decomposes after death.

Every fingerprint is unique!

WHAT IS A FINGERPRINT?

A fingerprint is a pattern comprised of ridges and valleys.A Ridge – is a high.A Valley – is a depression or low.

Friction ridges are also found on our palms, feet and toes.

Ridge Valley

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Fingerprint Principles• Individual characteristic

–Because no two fingers with identical ridge characteristics

• Remains unchanged during an individual’s lifetime

• General ridge patterns that permit systematic classification

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Anatomy of Fingerprints• 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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Anatomy of fingerprints• Dermal papillae

develop in the human fetus @ 3 months

• Enlarge during growth

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Anatomy of fingerprints• Finger touches a surface

–Perspiration–Oils from hairy portions of the body

–Transferred onto surface• Leaves fingerprint

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Fingerprint patterns• All fingerprints

– divided into three classes – Loops– Arches– whorls L.A.W.

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Loops• A loop must have one or more ridges

entering from one side of the print, re-curving, 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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Figure4.3  Loop pattern.

Loops

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Loops• Must have one

delta

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Whorls

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Whorls• Divided into four groups

–Plain–Central pocket loop–Double loop–Accidental

• All have a 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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Arches

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Arches• Least common of general

patterns–Plain arches–Tented arches

–Arches do not have deltas, or cores

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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 up-thrust or

spike

• The ridges meet at an angle that is less than 90 degrees

Questions???

How are fingerprints compared?A. Fingerprints are compared by noting the

ridge characteristics on two prints to determine whether or not they match.

B. An identification is established when a number of these characteristics occupy the same relative position on the two prints.

FINGERPRINT IDENTIFICATION

Fingerprints and a fingerprint classification schema involving six categories: (a) arch, (b) tented arch, (c) right loop, (d) left loop, (e) whorl, and

(f) double loop. Critical points in a fingerprint,called core and delta, are marked as squares and triangles.

FINGERPRINT IDENTIFICATION Henry Classification system

• Developed a method of classifying fingerprints. • modified by the FBI that allowed all set of 10

fingerprints in the world to be divided into 1024 groups.

Table 4.2 Frequency of fingerprints Loops WhorlsArchesUlnar radial plain other plain tented60% 5% 20% 10% 4% 1% loops = 65% whorl=30% arches =5%

RIDGE CHARACTERISTICS (Minutiae)

COMMON OCCASIONAL RARE

Ending Ridge

Bifurcation or fork

Dot

Eye or Enclosure

“T” Junction

Short Ridge

Trifurcation

Ridge Crossing

Row of Dots

Rid

ge C

hara

cter

istic

s

Use these characteristics as points of identification when comparing fingerprint samples. The more points you can find in common, the better the match!

RIDGE CHARACTERISTICS MAGNIFIED

Points 1, 2, 4, 5 are Ending Ridges

Points 8, 10, 11 are Bifurcations

Point 7 Short Ridge

Points 3 and 9 are Dots

Point 6 is an Enclosure (ISLAND)

1

2

4

5

8

1011

9

7

3

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Review of fingerprint types

ArchesArches are the simplest type of fingerprints that are formed by ridges that enter on one side of the print and exit on the other. No deltas are present.

Plain ArchRidges enter on one side and

exit on the other side.

Tented Arches Similar to the plain arch,

but has a spike in the center.

Spike or “tent”

LoopsLoops must have one delta and one or more ridges that enter and leave on the same side. These patterns are named for their positions related to the radius and ulna bones.

Delta

Ulnar Loop (Right Thumb)

Loop opens toward right or the ulna bone.

Radial Loop (Right Thumb)

Loop opens toward the left or the radial bone.

NOTE: On the left hand, a loop that opens to the left would be an ulnar loop, while one that opens to the right would be a radial loop.

WhorlsWhorls have at least one ridge that makes (or tends to make) a complete circuit. They also have at least two deltas. If a print has more than two deltas, it is most likely an accidental.

Draw a line between the two deltas in the plain and central pocket whorls. If some of the curved ridges touch the line, it is a plain whorl. If none of the center core touches the line, it is a central pocket whorl.

Plain Whorl

Central Pocket Whorl

Whorls – Part 2Accidental Whorl

Accidental whorls contain two or more patterns (not including the plain arch), or does not clearly fall under any of the other categories.

Double Loop Whorl

Double loop whorls are made up of any two loops combined into one print.

Delta

Delta

Identify each fingerprint pattern.

?A B

CD ERight

Hand

Left Hand

Left Hand

Right Hand

Right Hand

Presenting Fingerprints as Evidence

• No legal requirements on the number of points but generally the courts will accept 8 to 12 points of similarity as sufficient proof.

• Fingerprints do not lie but human error might account to wrongful convictions.

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Types of PrintsVisible & 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

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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

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Visualizing Latent Prints

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Detecting Prints• Hard nonabsorbent surfaces

–Glass, mirror, tile, painted wood–Developed by the application of a

powder–Can be lifted by clear tape &

examined

• Porous surfaces–Papers, cardboard, and cloth,

styrofoam, leather–Require treatment with a chemical

Ninhydrin• Reacts with amino acids left by

finger• Produces a orange /purple

color (Ruhemann’s purple)• Commonly used with paper

and porous surfaces

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Iodine Fuming• Heat iodine crystals (produces iodine

vapors)

• Combine with latent prints (react w/ oils on finger) to make them visible– Iodine prints are not permanent– Will fade– Must photograph the prints immediately– Works best on porous paper.

Silver nitrate• Reacts with the salt left from

sweat in a dried print .

• AgNO3 + NaCl AgCl *converts to dark Ag2O

• Turns prints brownish-purple

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Super Glue®

• Most widely used method to develop latent prints

• Best used on nonporous surfaces such as metals, glass, adhesive tapes and plastic.

• Leaves a white, permanent impression • can be treated with powders or fluorescent

dyes to create a sharper contrast.

• 98 to 99 percent cyanoacrylate ester

Super Glue fuming– Fuming chamber (for up to six hours)

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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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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.

Other methods

• Photograph

Digital Imaging- AFIS

• Digital image: of fingers are pressed against a glass plate and scanned to a screen.

** can be enhanced, compared and sent to AFIS within minutes. AFIS can compare hundreds of thousands of prints in less than a second.

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Digital Imagining: IAFIS• Replaced tradition method of fingerprinting.• Contains more than 55 million computerized

fingerprint records of known criminals.• Live Scan electronic fingerprints devices

transmit prints @ the time of arrest or booking to a central IAFIS database to provide immediate positive identification, check for with any suspect latent prints on file, and provide criminal history.