Transcript Fingerprinting

Fingerprinting
Why do we have fingerprints?
“Friction Ridge Skin”
 Provides a firm grasp & resists slippage.
► Found
on the palm side of fingers & hands,
soles of feet and toes.
► Formation
occurs during fetal development.
 Fingerprints do NOT change over a lifetime.
 Identical twins have different fingerprints!
 Fingerprints grow back when damaged.
Three (3) Types of Fingerprints
► Latent
 Invisible fingerprints.
 Formed when sweat, oil, amino acids, & water
are deposited in the formation of the ridge
pattern.
► Plastic
 Impressed into soft materials.
►Gum,
► Visible
wax, soap, dust, putty, etc…
or Patent
 Fingerprint left in a visible material
►Ink,
grease, blood, paint, etc…
Fingerprint Composition
► Sweat
 Eccrine sweat glands
►Produce
a “watery” sweat.
 Apocrine sweat glands
►Produce
► Proteins
► Lipids
an “oily” sweat
Skin Anatomy
► Epidermis
 Top Layer of Skin (2 mm in fingers)
 Contains keratin, melanin, & immune cells.
► Dermis
 Thick layer of connective tissue.
 Contains blood vessels, nerves, muscles, oil &
sweat glands, & hair follicles.
► Papillae
 Boundary between layers; forms ridge pattern.
Papillae
Major Ridge Patterns
► Loops
► Whorls
► Arches
LOOPS
► 60%
of population.
► Two (2) or more ridges entering from one
side, curving and exiting on the same side.
 Core
►Center
of loop
 Type Lines
►Ridges
that diverge
 Delta
►Closest
ridges to type lines;
forms a triangle.
Anatomy of a Loop
Types of Loops
► Radial
Loop
► Ulnar
 Loop opens towards thumb.
Loops
 Loop opens towards pinkie.
WHORLS
► 30%-35%
of population.
► Must have type lines and a minimum of
two (2) deltas!
► Four types:
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Plain Whorl
Center Pocket Whorl
Double Loop Whorl
Accidental
Types of Whorls
► Plain
Whorl
► Center
Pocket Whorl
Plain vs. Center Pocket Whorls
► Both
have at least one ridge that makes a
complete circuit.
Draw a line through the deltas.
Plain – hits the circuit ridge.
Center Pocket line does
NOT touch circuit ridge!
Types of Whorls
► Double
Loop Whorl
► Accidental
ARCHES
► 5%
of population.
► Simplest of all fingerprints!
► Ridges enter on one side of print and exit
on the other.
 Slight or dramatic rise in the center.
 Plain Arch vs. Tented Arch
► No
type lines or deltas.
Types of Arches
► Plain
Arch
► Tented
Arch
Fingerprint Analysis
► Used
► Not
to match a suspect to a crime scene.
based upon general shape or pattern.
► Requires
► Average
a point by point match of minutiae.
fingerprint has 150 minutiae.
 8 to 16 matches adequate in court.
 No statistical studies regarding locations of
common minutiae in populations.
Minutiae
► Ridges
– raised points on a print.
► Groves or Furrows – low points on a print.
 Minutiae (Ridge characteristics)
►Ridge
Endings
►Short Ridge
►Bifurcation
►Island or Dot
►Enclosure (or Lake)
►Crossover
Minutiae Mapping
Comparing Minutiae Maps
Latent Fingerprint Removal
► Depends
upon:
 Type of surface
►Porous vs. Nonporous
►Soft vs. Hard
 How the print was left.
►Visible vs. Invisible (latent prints)
 Amount of print available.
Latent Print Removal
► Dusting
► Superglue
Fuming
► Amino Acid Reaction
► Iodine Fuming
Dusting
► Surface:
 Smooth, nonporous.
► Chemical:
 Carbon black powder
► Method:
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Dust on powder with brush.
Remove excess powder (puff of air).
“Lift” print with tape.
Place on index card.
Superglue Fuming
► Surface:
 Smooth, nonporous.
► Chemical:
 Cyanoacrylate
► Method:
 Place print evidence in sealed container.
 Add few drops of superglue + heat.
 Takes 2-3 hours; chemical fumes stick to print.
Amino Acid Reaction
► Surface:
 Porous.
► Chemical:
 Ninhydrin
► Method:


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
Spray or dab chemical onto print area.
Allow to dry (2-3 hours).
Turns pink when it reacts with proteins.
Highly effective on old prints (up to 15 years!)
Iodine Fuming
► Surface:
 Porous.
► Chemical:
 Iodine crystals (solid)
► Method:
 Place print evidence in sealed container.
 Sublimation of iodine crystals.
►Solid
to GAS!
 Vapors attach to print.
 Not permanent! Must photograph!