Transcript FORENSIC SCIENCE - Ann Arbor Public Schools

FORENSIC SCIENCE
Fingerprints
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History
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3000 years ago: Chinese used fingerprints to
sign legal documents
1880: Henry Faulds suggested that friction
ridges be used to identify criminals. (Faulds actually
wrote a letter to Charles Darwin regarding fingerprinting but
Darwin thought that his cousin Galton would find it more
interesting.)

Several years before Bertillon: William
Hershel required natives of India to sign
contracts with the imprint of their right hand.
(There was a dispute between Faulds and Hershel over which of
the two was the first to propose fingerprints as a method of
identification.)
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History cont.
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1883 - Bertillon introduced anthropometrics
1891 – Dr. Juan Vucetich uses the work of Galton
to refine a classification system (still used in
Spanish speaking countries).
1892 – Galton describes loops, whorls, and arches
1897 – Sir Edward Henry develops the
classification system that is used in the U.S.
1924 – FBI Identification Division Established
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AFIS
Automated Fingerprint Identification System
AFIS is one of the three significant electronic
databases for law enforcement purposes.
There are two types of files:
1.
Knowns: Contains prints of known
individuals
2.
Forensic files: Consists of images from
unsolved cases
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Fundamental Principles
of Fingerprints

A fingerprint is an individual
characteristic.
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A fingerprint will remain unchanged
during an individual’s lifetime.
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Fingerprints have general
characteristics ridge patterns that
permit them to be systematically
classified.
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Ridge Characteristics
Minutia--lines of the fingerprint
ridge ending
bifurcation
short ridge island
dot or fragment island
enclosure
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MINUTIA
BIFURCATION
RIDGE ENDING
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MINUTIA
DOT or FRAGMENT
SHORT RIDGE
ISLAND
ENCLOSURE
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In Court

Courts require different amounts of matching
points of minutia
UK requires 16 points
Australia requires 12 points
FBI requires 12 points
U.S. courts require 6-8 points
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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
it began. Loops must have
one delta.
Types
Radial--opens toward the thumb
Ulnar--opens toward the “pinky”
(little finger)
Which type of loop is this, if on the
right hand? Left hand?
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Whorl
A plain or central pocket
whorl have at least one
ridge that makes a complete
circuit. A double loop is
made of two loops and an
accidental is not covered by
other categories.
Types
Plain
Central Pocket
Double Loop
Accidental
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Primary Identification
Numbers
Fingers are numbers 1 through 10 starting with the thumb on the
right hand and continuing through with the thumb on left hand.
Each finger is then given a point value as seen in the chart below.
1. right
thumb
16
6. left
thumb
4
2. right
index
16
7. left
index
2
3. right
middle
4. right
ring
5. right
little
8
8
4
8. left
middle
9. left
ring
2
1
10. left
little
1
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Primary Identification (cont)
Set up a ratio of even numbered fingers over odd numbered,
adding one in both the numerator and denominator.
2. right
index
16
4. right
ring
8
16
8
1. right
thumb
3. right
middle
6. left
thumb
4
4
5. right
little
8. left
10. left
middle
little
2
2
7. left
index
1
1
+
9. left
ring
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1
1
Fingers
1
2
2
16
1
16
8
8
4
4
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Tracking Down Fingerprints
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Patent Prints
Plastic Prints
Latent Prints
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Patent Prints

Patent prints occur when a substance such
as blood, ink, paint, dirt, or grease on the
fingers of the perpetrator of a crime leaves
behind a readily visible print.
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Plastic Prints

Plastic prints have a three-dimensional
quality and occur when the perpetrator
impresses a print into a soft substance
such as wax, putty, caulk, soap, cold butter
or even dust.
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Latent Prints
Latent fingerprints are those that are “hidden”
and are not visible to the naked eye. These
prints consist only of the natural secretions of
human skin and require treatment to cause
them to become visible.
Most secretions come from three glands:
Eccrine--largely water with both inorganic
(ammonia, chlorides, metal ions, phosphates) and
organic compounds (amino acids, lactic acids, urea,
sugars)
Apocrine--secrete cytoplasm and nuclear materials
Sebaceous --secrete fatty or greasy substances.
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Skin Layers
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Lifting Latent Prints
Here’s where the chemistry comes in……..
Developing a print requires chemicals that react
with secretions that cause 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 the
background.
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Lifting Latent Prints (cont)

Iodine-- fumes react with oils and fats to produce a
temporary yellow brown reaction.
Ninhydrin--reacts with amino acids to produce a purple
reaction.
Silver nitrate--react with chlorides to form silver chloride,
a material which turns gray when exposed to light.
Cyanoacrylate--”super glue” fumes react with water and
other fingerprint constituents to form a hard,
whitish deposit.
In modern labs and criminal investigations, lasers and
alternative light sources are used to view latent fingerprints. It
was first used by the FBI in 1978. Since lasers can damage the
retina of the eye, special precautions must be taken and a filter
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used.
Iodine Fingerprint
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Ninhydrin Fingerprint
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Cyanoacrylate Fingerprints
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Will West & William West
May 1, 1903 – Will West went to
Leavenworth Penitentiary in Kansas.
The clerk thought that he looked familiar
but Will denied ever being there.
Coincidentally, there was another inmate
named William West. They looked very
much the same and had the same
Bertillon anthropometric measurements
but they denied ever knowing each other.
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Will West & William West
Fingerprints helped authorities distinguish
between the two Wills. So much for measuring the
width of a person’s head. Leavenworth
immediately dumped the Bertillon anthropometric
system and switched to a fingerprint system.
P.S. This wasn’t just a bizarre coincidence. A report in the Journal of
Police Science and Administration in 1980 revealed that they were
indeed identical twins and each wrote letters to the same brother and
five sisters and the same Uncle George.
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Bertillon’s Embarrassing Moment
Bertillon reluctantly agreed to add
fingerprints to his bertillonage
profile. However, he added only
those of the right hand.
Big mistake!
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This is where Mona Lisa
comes in…
On August 21,1911, Leonardo da Vinci’s
famous painting Mona Lisa was stolen
from the Louvre Museum in Paris. The
thief left a clear thumbprint on the glass
that had protected the masterpiece. No
system of classification had been devised
yet so Bertillon and his assistants spent
several months digging through his files.
They found no match.
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Mona Lisa cont.
Two years later police apprehended the thief,
Vicenzo Perugia. His prints matched the ones
found at the newest crime scene. It turns out
that Perugia’s prints were among those in
Bertillon’s possession the whole time. No
match had turned up because the print found
at the scene of Mona Lisa was from Peruglia’s
left thumb and Bertillon’s files contained only
that of Peruglia’s right thumb.
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It’s thumbthing to think about…
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