what are fingerprints? - kentchemistry.com€¦ · three categories of fingerprints •plastic...
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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
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
Cross-section of human skin
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
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
Second Principal: Fingerprints
are Unchanged through Life
• Friction ridge pattern of skin develops in
utero (before birth)
• Pattern remains unchanged throughout life
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)
Left middle fingerprint
Permanent scar
Third Principal: General Patterns
allow systematic classification
• The 3 basic fingerprint patterns
1. Loops (60-65%)
2. Whorls (30-35%)
3. Arches (5%)
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
Fingerprint patterns
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
bsapp.com
bsapp.com
Ulnar Loops
Opens toward the
little finger
Print from the right hand
bsapp.com
bsapp.com
Radial Loops
Opens toward
the thumb
Print from the right hand bsapp.com
Arches • Formed by ridges entering from
one side of the print, rising
slightly and exiting on the
opposite side.
• No Deltas
• No Cores
Arch patterns
Whorls
• One or more cores
• At least two deltas
Whorl patterns
Plain Whorl
• At least one ridge makes complete
circuit
– Can be spiral, oval, or any variant of a
circle
bsapp.com
Plain Whorl
• Two Deltas
• One Core
• Symmetry
Central Pocket Loop
• Two Deltas
• One Core
• Lacks Symmetry
• A delta is often near the core
Double Loop
Two loops combined into one
fingerprint
bsapp.com
Double Loop
• Two Deltas
• Two Cores
• Appears to
have an “S” in the print
bsapp.com
Accidental
• All other
prints that
cannot be
classified in
the other
groups
bsapp.com
Fingerprint ridge characteristics
Loop pattern
Fingerprint ridge characteristics
Individual vs. Class Evidence
Class Evidence
• General pattern
(L.A.W)
Individual Evidence
• Minutiae patterns
• Scars, etc.
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