ch. 14 fingerprints · history of fingerprints •17921750 b.c. clay tablets in babylon •1000b.c....
TRANSCRIPT
1Dec 16 1:25 PM
Ch. 14 Fingerprints
http://www.idfpr.com/DPR/images/fingerprint.gif
2Dec 16 1:30 PM
Essential Questions:
What is it about fingerprints that make them so unique?
How are fingerprints used by a forensic scientist?
3Dec 16 1:50 PM
History of fingerprints• 17921750 B.C. clay tablets in Babylon• 1000B.C. Chinese to sign legal documents• Hershel in India required fingerprint on contracts• 1856 Sir William Hershel collected prints• 1880 Fauld recognized use of fingerprints for identification• 1892 Galton published book on topic
assigned patterns• 1896 Sir Edmund Richard Henry groupings based on ridge patterns (loops, whorls, arches)• 1901 NYC used to certify civil service applications• 1924 FBI system started
4Dec 16 1:32 PM
fingerprint an impression of the pattern of ridges on the last joint of a person's finger
formed between 100120 days of fetal development
properties for identification:1. unique ridges2. consistency over a person's lifetime3. systematic classification used for fingerprints
5Dec 16 1:43 PM
Why do we have ridges?
better gripmakes perspiration easier on hairless surfacesense of touch increased
(apes and monkeys also have ridge patterns)
6Dec 16 3:13 PM
Where do the ridges come from?
dermal papillaelayer
7Dec 16 3:15 PM
John Dillinger gangster (1930's) tried to have his prints destroyed
applied acid caused scar tissue to form (also characteristic)
still had plenty of minutiae to identify him
some professions can affect fingerprintschemists, concrete workers, plasterers
8Dec 16 1:58 PM
*Individuality is not based on pattern, but on ridge characteristics
*average person has about 150 ridge patterns
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Basic patterns of ridges
loop arches whorls
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loop 1 or more ridges entering from 1 side, curving, then going out the same side it entered
have a delta triangular area
have a core near center of pattern
About 65% of all fingerprints are loops
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Ridge count can also be used to distinguish between prints
from center of core to edge of delta, count # of ridges)
12Dec 16 2:06 PM
2 subgroups:radial loop opens towards the thumb
http://shs.westport.k12.ct.us/forensics/04fingerprints/handout.htm
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ulnar loop opens towards the pinky*need to know which hand the print came from to determine which type
http://shs.westport.k12.ct.us/forensics/04fingerprints/handout.htm
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Arch friction ridges enter from one side of the finger and exit the other while rising in the center
no delta or core
~5% have arches
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two types of arches:
plain4% tented1%
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whorl roughly circular, with ridge lines going all the way around
2 deltas on opposite sides of whorlhas a core
core
deltas
~3035% have whorls
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four whorl patterns:
plain 24%
central pocket 2%
double loop4%accidental(2 or more patterns)(0.01%)
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ten print card for fingerprints
19Dec 16 2:39 PM
Edward Henry primary classification system(based on presence of whorls)
R. Index R. Ring L. Thumb L. Middle L. Little 1 + + + + + =R. Thumb R. Middle R. Little L. Index L. Ring 1
16 8 4 2 1
The presence of a whorl in any of the pairs above earns the value below the pair (i.e., a whorl on the Right Ring finger earns an 8 in the numerator, whereas a whorl on the left index finger earns a 2 in the denominator. The absence of a whorl in other words you have either a loop or an arch earns a zero for that finger.).
20Dec 16 2:44 PM
Unlike actual fractions, we will be adding the numerators and the denominators, so it is best not to think of these as actual fractions! We will also add a one to both numerator and denominator to get the final "fraction" classification:
right right left left left add automatically finalindex ring thumb middle litle group
+ + + + + 1____ ____ ____ ____ ____ _____ =
+ + + + + 1
right right right left left added automatically finalthumb middle little index ring group
There are 1024 possible groupings. About 25% of the population has no whorls.
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Advantage of this system can weed out most of the fingerprints on file
22Dec 16 2:57 PM
How to individualize groups:
minutiae ridge characteristic detailsBasic and composite ridge characteristics (minutiae)
Minutiae Example Minutiae Example
ridge ending bridge
bifurcation double bifurcation
dot trifurcation
island (short ridge) opposed bifurcations
lake (enclosure) ridge crossing
hook (spur) opposed bifurcation/ridge endingTaken from <http://www.policensw.com/info/fingerprints/finger08.html>
23Dec 16 3:06 PM
This image is from <http://perso.orange.fr/fingerchip/biometrics/types/fingerprint.htm>
24Dec 16 3:09 PM
Presenting fingerprints as evidence
criminal courts 812 minutiae as proof
25Dec 16 3:20 PM
Types of prints:
1. plastic (aka indented or molded)pressing a finger against a plasticlike material to form a negative impressionex. fresh paint, putty, candle wax, gum on envelopes, softened candy
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2. Patent (visible) prints left by a finger touched onto colored material such as blood, paint, ink, grease, mud, chalk
3. Latent invisible prints that must be developed, left by body oils and perspiration
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Procedures for processing fingerprints:
I. Dusting on nonporous surfaces
powderDusting is ideal on wood, metal, glass, plastics, Formica, and tile. It is less than ideal on paper, cardboard, and leather.
powder should be contrasting color to surface
pour powder on a piece of paperdip fingerprint brush in powder and shake out excess powderapply brush to object in a rotary motion to keep with pattern of fingerprint
28Dec 199:26 PM
use wax pencil to number print (number in sequence taken)
use clear tape to lift print place tape over print and wax pencil marking
place lifted print on a backing of contrasting color to the powder
package label includes case number, lift/item number, location of print, date, time and person lifting print
29Dec 199:41 PM
II. Other processing methodsa.Super glue (cyanoacrylate)
a big storage container or aquarium along with a hotplate A few drops of superglue is placed on the hotplate, and the object containing prints is placed into the container. The hotplate is turned on, the container is sealed, and in about fifteen or twenty minutes, any prints that were invisible are now visible in grayish tone on the objectcan then treat with fluorescent dye, UV light
30Dec 199:48 PM
b. Ninhydrinused for all kinds of surfaces, including books and wallpaper develops prints that may be very old, made over 30 years ago.reacts with oils of latent print produces a blueviolet color on the developed print. area is sprayed until it is damp but not saturated. Need ventilation Drying takes from ten to twenty minutes, but the process can be speeded up by using a heat lamp.
31Dec 199:52 PM
c. Iodine fumingporous surfaces such as paper and unfinished woodcrystal iodine heated in fume chambercombines with oils in printproduces brownish printfades so has to be photographed quickly or preserved with starch solution
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d. silver nitrateprint exposed to silver nitratechloride in salt in print reacts with silver nitrate and forms silver chlorideunder UV light black or reddish brown print
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When fingerprint evidence is photographed: a complete record of all technical data about the camera, lens, film, shutter speed, lens opening, illumination, camera position, distance from object, and angle is also kept. (This protects the police department from charges that it's the photography which makes it look like a match.)
household furnishings are usually protected with a drop cloth while police are dusting for prints.
With photos, three different exposures are usually taken: a regular exposure, an underexposure, and an overexposure.
34Dec 192:49 PM
AFIS (Automated fingerprint Identification Systems) 199947 million people
a. Index systemsstore "MO", individual characteristics, fingerprint classificationcomputerized
b. Ridgeangle systems angle of ridge flow on ten print card stored
c. Encoded minutiae systemsten print cards or latents scanned and minutiae mapped
35Apr 46:53 AM