fingerprints. chapter 4 fingerprints 2 kendall/hunt publishing company 2 fundamental principles of...
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Fingerprints
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Fundamental Principles of Fingerprints
A fingerprint is an individual characteristic.
A fingerprint remains unchanged during an individual’s lifetime.
Fingerprints have general characteristic ridge patterns that permit them to be systematically classified.
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All fingers, toes, feet, and palms are covered in small ridges.
These ridges are arranged in connected units called dermal, or friction, ridges.
These ridges help us get or keep our grip on objects.
Natural secretions plus dirt on these surfaces leave behind an impression (a print) on those objects with which we come in contact.
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There are 3 main fingerprint patterns found in the human population:
Loops: found in 60% of the population Whorls: found in 30% of the population Arches: found in 10% of the population A typical loop must have one or more ridges
that enter from one side, loop, and then exit from the same side.
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October 4, 2011: Activity – page 77 # 1
Look at your fingerprints under the magnifying glass. Draw each of your prints in the boxes on the worksheet. Figure out whether they have arches, whirls, or loops.
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Fingerprint Analysis – page 77 - # 2 Inkprint all of your fingerprints Students work in groups of four: Compare your
fingerprints to the other people in your group 1. What were some similarities in your group? 2. What were some differences in your group? 3. What are some problems you can foresee when using
fingerprints to identify people? 4. What are some questions you have that you want
answered by the end of this unit?
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AFIS
The Automated Fingerprint Identification System—a computer system for storing and retrieving fingerprints
Established in the 1970s
IAFIS—the FBI’s Integrated Automated Fingerprint Identification System, which is a national database of all 10-print cards from all over the country
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Fingerprint Minutiae
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LOOP WHORL ARCH
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Arch
An arch has friction ridges that enter on one side of the finger and cross to the other side while rising upward in the middle. They do NOT have type lines, deltas, or cores.
Types
Plain
Tented
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Loop A loop must have one or more ridges entering and exiting from the same side. Loops must have one delta. A double loop is made of two loops.
Types
Radial—opens toward the thumb
Ulnar—opens toward the “pinky” (little finger)
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Whorl
A plain or central pocket whorl has at least one ridge that makes a complete circuit. An accidental is a pattern not covered by other categories. Whorls have at least two deltas and a core.
TypesPlainCentral pocketDouble loopAccidental
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Primary Classification
The Henry-FBI Classification System
Each finger is given a point value.
right left
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Primary Classification, continued
Assign the number of points for each finger that has a whorl and substitute into the equation:
right right left left left index ring thumb middle little + 1
right right right left left thumb middle little index ring + 1
That total number is your primary classification number.
=
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Comparison
There are no legal
requirements in the
United States on the
number of points required
for a match. Generally,
criminal courts will accept
8 to 12 points of
similarity.
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Latent Prints
Latent fingerprints are those that are not visible to the naked eye. These prints consist of the natural secretions of human skin and require development for them to become visible.
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Developing Latent Prints
Developing a print requires substances that interact with secretions, causing the print to stand out against its background. It may be necessary to attempt more than one technique, done in a particular order so as not to destroy the print.
Powders—adhere to both water and fatty deposits. Choose a color
to contrast with the background.
Iodine—fumes react with oils and fats to produce a
temporary yellow-brown color.
Ninhydrin—reacts with amino acids to produce a
purple color.
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Iodine Fingerprint
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Other Prints
Lips—several common patterns
Voice—electronic pulses measured on a spectrograph
Foot—size of foot and toes; friction ridges on the foot
Shoes—can be compared and identified by type of shoe, brand, size, year of purchase, and wear pattern
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Other Prints, continued
Palm—friction ridges can be
identified and may be used
against suspects
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Other Prints, continued
Footprints are taken at birth
as a means of identification of
infants.
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Other Prints, continued
A man has been convicted of suffocating an eldery woman on the basis of earprint evidence. The assailant was caught after police matched the inprint of his ear on the victim’s window. Police believe that the thief put his ear to the window to listen for signs of anyone home.
Earprint catches murderer
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Other Prints, continued
Teeth—bite marks are unique and
can be used to identify suspects.
These imprints were placed in gum
and could be matched to crime
scene evidence.