what are fingerprints? - kentchemistry.com€¦ · three categories of fingerprints •plastic...
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![Page 1: What Are Fingerprints? - kentchemistry.com€¦ · Three Categories of Fingerprints •Plastic prints –Created when the fingers touch against some material such as putty •Patent](https://reader034.vdocuments.us/reader034/viewer/2022042710/5f6594a25d677327df343d53/html5/thumbnails/1.jpg)
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What Are Fingerprints?
• Friction ridges are found on skin of
– palms of hands
– palmar aspect of fingers
– soles of feet
– solar aspect of toes
• Designed by nature for firmer grip and
resistance to slippage
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Skin Structure
• Epidermis = outer, surface layer of skin
• Dermis = inner layer of skin
• Dermal papillae = area between dermis
and epidermis
• Papillary pattern determines the form
and pattern of the friction ridges on
skin surface
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Cross-section of human skin
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Uses of Fingerprints
Can be used to identify:
• Suspects
• Victims
• Other persons who touched a surface
• A corpse
• People who might use aliases to disguise their illegal intent
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First Principal: Fingerprints are
Unique
• Millions of prints taken over 90 years
• No two fingers have yet been found to have
identical ridge characteristics (minutiae)
• Identical (monozygous) twins
– have same DNA
– have different fingerprints
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Second Principal: Fingerprints
are Unchanged through Life
• Friction ridge pattern of skin develops in
utero (before birth)
• Pattern remains unchanged throughout life
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Do fingerprints remain
unchanged?
• Impossible to do, but many have tried
– John Dillinger-corrosive acid
• To change the pattern requires
obliteration of the dermal papillae (1- 2
mm deep)
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Left middle fingerprint
Permanent scar
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Third Principal: General Patterns
allow systematic classification
• The 3 basic fingerprint patterns
1. Loops (60-65%)
2. Whorls (30-35%)
3. Arches (5%)
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Three Categories of
Fingerprints
• Plastic prints – Created when the fingers touch against some
material such as putty
• Patent or visible prints – Formed when the fingers are contaminated with
such things as ink or blood and touch a clean surface
• Latent/invisible prints – Left on a surface from the small amounts of body
oil and perspiration that are normally found on friction ridges
– visible
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Fingerprint patterns
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Loops
• Must have:
– One or more ridges that enter from one
side of the print, re-curve, and exit from
the same side
– One Delta
– One Core
bsapp.com
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bsapp.com
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bsapp.com
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Ulnar Loops
Opens toward the
little finger
Print from the right hand
bsapp.com
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bsapp.com
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Radial Loops
Opens toward
the thumb
Print from the right hand bsapp.com
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Arches • Formed by ridges entering from
one side of the print, rising
slightly and exiting on the
opposite side.
• No Deltas
• No Cores
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Arch patterns
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Whorls
• One or more cores
• At least two deltas
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Whorl patterns
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Plain Whorl
• At least one ridge makes complete
circuit
– Can be spiral, oval, or any variant of a
circle
bsapp.com
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Plain Whorl
• Two Deltas
• One Core
• Symmetry
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Central Pocket Loop
• Two Deltas
• One Core
• Lacks Symmetry
• A delta is often near the core
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Double Loop
Two loops combined into one
fingerprint
bsapp.com
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Double Loop
• Two Deltas
• Two Cores
• Appears to
have an “S” in the print
bsapp.com
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Accidental
• All other
prints that
cannot be
classified in
the other
groups
bsapp.com
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Fingerprint ridge characteristics
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Loop pattern
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Fingerprint ridge characteristics
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Individual vs. Class Evidence
Class Evidence
• General pattern
(L.A.W)
Individual Evidence
• Minutiae patterns
• Scars, etc.
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