Transcript File - Forensic Science

FORENSIC SCIENCE
Fingerprints
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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
1) A fingerprint is an individual
characteristic.
2) A fingerprint will remain unchanged
during an individual’s lifetime.
3) Fingerprints have general
characteristics ridge patterns that
permit them to be systematically
classified (arch, loop or whorl).
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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
ISLAND
SHORT RIDGE
ENCLOSURE
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MINUTIA
Exits: describes
the direction of
lines coming in
or out
How many exits and deltas
are present?
Deltas: triangle
with ridges
radiating
outward in 3
directions.
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Fingerprint Patterns
Arch
 Loop
 Whorl

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Arch
An arch has 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.
Summary:
• Exits: 2
• Deltas: 0
Least common pattern (5%)
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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.
Summary:
• Exits: 1
• Deltas: 1
*Most common pattern (60%)*
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Whorl
A whorl has at least one
ridge that makes a
complete circuit and two
points of delta
Summary:
• Exits: 0
• Deltas: 2
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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
+
1
1
9. left
ring
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Fingers
1
2
2
16
1
16
8
8
4
4
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Dactyloscopy

the practice of using
fingerprints to identify
someone
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Tracking Down
Fingerprints
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 threedimensional 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.
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Latent Prints
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.

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Lifting Latent Prints (cont)

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 used.
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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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Homework Questions
1. What is dactyloscopy?
2. List and describe (exits and deltas) the 3
fingerprint patterns.
3. Draw the following minutia:
A. bifurcation
B. short ridge
4. Identify and describe the 3 kinds of fingerprints
(not patterns).
5. List the different ways in which we can lift prints.
What color do prints appear for each method?
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