Fingerprints
A Brief History
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Chinese: 3000 yrs. Ago, Chinese used fingerprints to sign legal
documents
Henry Fauld (1890): Suggested finger ridges could be used to identify
criminals.
William Herschel (1870): English civil servant in India; required natives
of India to sign contracts with the imprint of their right hand.
Alphonse Bertillon: Anthropometry-no two people have the same 11
measurements. Used 11 body measurements to identify individuals.
Included height reach, width of hand, length of left foot, etc…
Francis Galton: Published the book “Fingerprints.” Described 3 main
fingerprint patterns; arches, loops, and whorls.
United States: Henry System (1899)-Developed a fingerprinting system
used by the FBI to date. First used by the NYC Civil Service
Commission. FBI currently has the largest collection of fingerprints in
the world.
United States vs.Byron C. Mitchell (1999): A defendant’s attorney
argued that fingerprints could not be proven unique. Judge upheld, said
fingerprints were unique and could be admissible in court.
Fingerprint Anatomy
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Human skin is the first line of defense.
2 layers--epidermal and dermal
Papillae- Boundary between the 2 layers, that contain the ridge patterns.
Sweat glands secrete oil that leaves an identification residue conforming the ridge
pattern.
sweat pores
Epidermal
Papillae
Dermis
Sweat gland
Fundamental Principles of Fingerprints
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1-A fingerprint is an individual characteristic; no two fingers have yet to
possess identical ridge characteristics.
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Individuality of a fingerprint is not determined by the general shape, but by the
examination of ridge characteristics (minutiae)
Type, number, and location of ridge characteristics
-Fingerprints have
150 different
characteristics.
-match 8-16 for an
identification.
Fundamental Principles of Fingerprints
• 2- A fingerprint will remain unchanged during an individual’s
lifetime.
-Fingerprints form in the 17th week of gestation
-Twins do not have matching fingerprints.
-If a person tries to change the print:
1- 1-2 mm below the surface
2- Leaving scars
Fundamental Principles of Fingerprints
• 3- Fingerprints have general ridge patterns that permit
them to be systematically classified.
- All prints can be classified as a loop, whorl, or arch
-Print:
Core (center), Deltas-form triangles on the side of the print
65% of all fingerprints in the world are loops.
Fundamental Principles of Fingerprinting Cont.
Loop
A loop must have one or more ridge lines entering from one side of
the print, recurving, and exiting from the same side.
Fundamental Principles of Fingerprinting Cont.
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30% of the population have whorls
Must have two deltas
Resembles a Bull’s eye or target
Fundamental Principles of Fingerprinting Cont.
Arch
5% of the population have arches
The ridge lines enter from one side of the print and exit from
the opposite side.
Fingerprint Classification
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Several steps
Used as the first step in a crime scene
Must identify the presence of a whorl
Assign a numerical value based on the finger it (whorl) was found on
Used to search databases
Example: Right index and right middle fingers are whorls and all the others are loops.
Automated Fingerprint Identification Systems
AFIS
• Uses automatic scanning devices that convert the image of a
fingerprint into digital image characteristics that contain data
showing ridges at their points of termination or splits in the
ridge.
• 40,000 new prints everyday
• Identifies 8,000 fugitives a month
• Looks at 67 years in 20 mins.
Methods of Detecting Fingerprints
Visible Prints
Occur when a finger
has been placed in a
colored substance like
blood, paint, ink, mud,
etc.
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Non-Porous Surfaces
Hard, smooth, nonabsorbent, glass,
mirror, painted wall
Latent Prints
“lie hidden”
Prints appear invisible,
can be developed to be
seen.
Plastic Prints
Prints that are
made in soft
substances like wax,
soap, plastic
3D model of print
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Porous Surfaces
Soft, absorbent materials
Cloth, ceramic, concrete
Common Techniques Used
1. Dusting with Carbon Powder on white or light colored surfaces.
Color contrast
Dust gets stuck in oil of print
Use tape to lift print
2. Dusting with Lanconide Powder for black surfaces.
White powder
Gives color contrast
3. Dusting with Aluminum Powder for hard or dark colored surfaces as well as mirrors and
metal surfaces.
Color contrast
Magnetic
4. Use of Cyancacrylate (Super-Glue) fuming
Fumes polymerize and harden in the oils of the print
Must dust the print afterwards
Methods of Detecting Fingerprints Cont.
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5. Use of Iodine Fuming techniques
-Iodine crystals sublime (5-7g)--goes from solid to gas at room temperature.
-Gas sticks to print-not permanent--need to take pictures
6. Use of ninhydrin
-Reacts with the protein in the print
-Often used on porous surfaces
7. Use of Silver Nitrate
-Reacts with sodium chloride (salt) in the oil.
8. Use of Gentian Violet
-Fluoresce the print--print will glow
9. Use of Laser Technology
-Using dyes and wave lengths of light, you can get the print to glow.
Preservation of Prints
-Prints are often lifted with tape
and them placed on a card
-Contrasting background
-Photograph is taken
Digital Imaging
-Picture id transferred to a digital image.
-Once the image is stored, it can be
manipulated for better resolution.
-Used to compare prints side by side
-Only good as image produced