Transcript Notes on Fingerprints

CSI: Mohawk
Chapter 4
Identification and Fingerprinting
Bertillon System
• Developed by Alphonse Bertillon in 1883
• Included
– Detailed description
– Full-length & profile photos
– Anthropometry -- precise body measurements
Bertillon Measurements
Image form: http://criminaljustice.state.ny.us/ojis/history/measure.jpg
Bertillon Measurements
• Height
• Left shoulder to middle
finger of raised right arm
• Seated, length from top of
head to seat
• Back of head to forehead
• Temple to temple
• Length of right ear
• Length of left foot
• Length of left middle
finger
• Left elbow to tip of left
middle finger
• Width of cheeks
• Length of left pinky
The Will West Case
True Story?
• Will West convicted and sent to Leavenworth
penitentiary in KS
• Bertillon measurements taken
– Matched those of William West
• William West still in prison
• Men looked almost identical
• Fingerprints different
• Turning point in identification?
Fingerprints Left at a Scene
• Plastic
– Prints left behind on a soft surface
• Visible
– Fingers came in contact with something else
• Blood
• Paint
• Mud
• Latent
– “Hidden”
– Not visible to the naked eye
Detecting Latent Prints
• Dusting
– For hard, smooth surfaces
• Metal, glass, painted surfaces, etc.
– Powders used
• Aluminum for dark surfaces
• Carbon for light surfaces
• Magnetic or fluorescent for various colors and textures of
surfaces
– How does it work?
• Powder adheres (sticks to) perspiration and oils left behind
from fingers
Detecting Latent Fingerprints
• Iodine Fuming
– For porous surfaces
• Paper, wood, etc.
– IODINE IS TOXIC
– How does it work?
• Iodine sublimes (solid --> gas)
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Reacts with oils from print
Brownish print now visible
Fades quickly
May be “fixed” by spraying with starch solution
Detecting Latent Fingerprints
• Ninhydrin
– Also for nonporous surfaces
– Takes at least an hour to develop
– How does it work?
• Spray/brush on surface
• Reacts with amino acids left behind
– YOU are made of amino acids. Wear gloves or IT WILL
REACT WITH YOU!
• Leaves behind blue-purple print
• Development can be quickened with heat
Detecting Latent Fingerprints
• Silver Nitrate
– How does it work?
• Spray/brush on surface
• Reacts with salt left behind
– IT IS TOXIC IF INGESTED AND WILL STAIN YOUR SKIN!
• Leaves behind dark print
Detecting Latent Fingerprints
• Super Glue (cyanoacrylate ester) Fuming
– Also for nonporous surfaces
– How does it work?
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Small amount of glue placed in closed container with item
Fumes vaporize, particularly in warm temps
Fumes from glue adhere to print
Leaves white, less fragile print behind that may further be
dusted
• Handheld device now available that combines Super Glue with
fluorescent dye
Analyzing Fingerprints
• Why is this useful?
– No two individuals have been found to have the
same fingerprint patterns.
• Not even identical twins
– Fingerprints can be used to link a suspect to a
crime scene.
Major Classes of Fingerprints
• Arches
– No deltas (triangular section)
– No core (center)
• Loops
– One delta
– One core
• Whorls
– Two deltas
– One core
Primary Classification of Prints
R. Index + R. Ring + L. Thumb + L. Middle + L. Little + 1
R. Thumb + R. Middle + R. Pinky + L. Index + L. Ring + 1
•Fraction used to group people into categories
•Made searching for match easier (before computers anyway)
•Only useful if full set known
•16/8/4/2/1 if whorl, 0 if other
=
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?
Subcategories of Prints
• Whorls
– Plain whorl
• All circular
• Circle touches or just above line connecting deltas
– Central pocket loop whorl
• Opens to one side
• Pattern crosses line connecting deltas
– Double loop whorl
• Two loops that wrap around each other
– Accidental whorl
• Any whorl that does not fit into the above categories
• Could have components of more than one of the above subtypes
Subcategories of Prints
• Loops
– Ulnar loop
• Opens toward pinky
– Radial loop
• Opens toward thumb
Subcategories of Prints
• Arches
– Plain arch
• Smooth hill-like pattern from one side of print to
other
– Tented arch
• Sharp peek in center (looks sort of like a delta)
Making a Match
• Category of print is not enough
• Individual characteristics of friction ridges
must be examined
• Many agree that 16 matching ridge
characteristics warrant a match
Making a Match
• Types of ridge characteristics or minutiae (min-oosha)
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Ridge ending -- point where line stops
Bifurcation -- point where line splits in two
Lake (eye) -- point where two lines surround small area
Short ridge -- not very long line
Dot -- about the same width and length
Spur -- short line coming from bifurcation point
Bridge -- short line that connects two other lines
Ridge crossing -- two lines switch
Automated Fingerprint
Identification System (AFIS)
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Fingerprint scanned
Image converted to digital record of pattern
Much faster than conventional methods
Provides a list of possible matches
– Results then examined by fingerprint expert
Heredity of Fingerprint Patterns
• Fingerprints are hereditary.
– L gene dominant
– l gene recessive
• Combinations
– LL = whorl
– Ll = loop
– ll = arch
• Though the passing on of traits is more
complicated, this offers a simplification of what is
actually going on.
Probability and Fingerprints
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Expressed as percent or fraction
In fraction form, P = n/N
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n = number of one outcome
N = number of all possible outcomes
Example
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60% of fingerprints are ulnar loops
This means 60 out of 100, or 60/100.
Reduce the fraction to get 3/5.
This means the probability of a fingerprint being an
ulnar loop is 3 out of 5.
Probability and Fingerprints
Pattern
Frequency
Ulnar loop
60%
Radial loop
5%
Plain whorl
20%
Other whorls
10%
Plain arch
4%
Tented arch
1%
• Probabilities are
multiplicative
• What is the probability
that a person will have a
plain whorl and a plain
arch?
(20/100)x(4/100)
Reduce: (1/5) x (1/25)
Multiply:1/125
One in 125 people will have
both.
Probability vs. Odds
• P = n/N
• Odds = n/(N-n)
• The probability of a fingerprint being an ulnar
loop was 3/5. This means the odds of a print
being an ulnar loop are 3 to 2. (For every 3 that
are, 2 are not.)
• The probability of someone having a plain whorl
and a plain arch was 1/125. This means the odds
of a person having this combination are 1 to 124.
Works Consulted
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Neff, Scott, The InfoJustice Journal, “Forensic Science, History, and Methods
of Identification for Agent and Investigators,”
http://www.infojustice.com/samples/06fingerprint.htm, accessed February
2007.
Olsen, Robert D., “A Fingerprint Fable: The Will and William West Case,”
http://www.scafo.org/library/110105.html, accessed February 2007.
Saferstein, Richard, Criminalistics: An Introduction to Forensic Science, 7th
ed., New Jersey, Prentice Hall, Inc., 2001.
Wikipedia, the Free Encyclopedia, “Anthropometry,”
http://en.wikipedia.org/w/index.php?title=Anthropometry&oldid=105126904,
accessed February 2007.