Transcript Fingerprints

Fingerprints
Dermatoglyphics and Dactyloscopy
SFS1. Students will recognize and classify various types of evidence in relation
to the definition and scope of Forensic Science.
b. Distinguish and categorize physical and trace evidence (e.g. ballistics, drugs,
fibers, fingerprints, glass, hair, metal, lip prints, soil, and toxins).
SFS2. Students will use various scientific techniques to analyze physical and
trace evidence.
a. Identify and utilize appropriate techniques used to lift and evaluate readable,
latent, plastic and visible fingerprints.
ESSENTIAL QUESTIONS
1.
2.
3.
What are the basic principles underlying
the forensic use of fingerprints?
How can you use minutiae to identify and
distinguish prints?
How can you use patterns to identify and
distinguish prints?
ESSENTIAL QUESTIONS
4.
5.
How can you identify and distinguish the
three types of transfer prints?
What methods are used to detect and
visualize specific types of prints?
History
 The
first systematic attempt at
personal identification was devised in
1882 by a French police expert,
Alphonse Bertillon.
The
Bertillon system relied on a detailed
description of the subject, combined with
full length and profile photographs and a
system of precise body measurements
called anthropometry.
History

In 1892 Francis Galton published his
classic textbook Finger Prints.
 At
Galton’s insistence, the British government
adopted fingerprinting as a supplement to the
Bertillon system.

The next step was the creation of
classification systems capable of filing
many thousands of prints in a logical and
searchable sequence.
 Sir
Edward Henry devised a classification
system between 1896 and 1925.
History

In 1903, when the
Bertillon system
could not distinguish
between two men
(Will West and
William West), it was
fingerprinting that
clearly distinguished
them.
What is a fingerprint?




Fingerprints are a reproduction of epidermal friction
skin ridges found on the palm side of the fingers and
thumbs, the palms, and soles of the feet.
During fetal development, friction ridges are formed
and are permanent throughout life until death and
decomposition.
These friction areas have a series of lines made up
of hills (ridges) and valleys (furrows).
These are specialized for traction and enhanced
sensory perception.
Fingerprint Principles

The basic principles underlying the use of
fingerprints in criminal investigations are that:
(1) a fingerprint will remain unchanged during
an individual’s lifetime;
(2) fingerprints have general ridge patterns
that permit them to be systematically
classified; and
(3) a fingerprint is an individual characteristic
because no two fingers have yet been
found to possess identical ridge
characteristics.
Fingerprints are permanent
The epidermis is the outer layer of the
skin, while the dermis is the inner layer of
the skin.
 The dermal papillae is the layer of cells
between the epidermis and dermis, that is
responsible for determining the form and
pattern of the ridges on the surface of the
skin.


Once the dermal papillae develop in the
human fetus, the ridge patterns will remain
unchanged throughout life except to
enlarge during growth. Thus, a fingerprint
will remain unchanged during an
individual’s lifetime.

Injury can alter a fingerprint, but the damage
must extend 1-2mm into the dermis.
Fingerprints have patterns

All fingerprints are divided into three
classes on the basis of their general
pattern: loops, arches, and whorls.
60% of people have loops
35% have whorls
5% have arches
Loops

A loop must have one or more ridges
entering from one side of the print,
recurving, and exiting from the same side.

All loops have one core
and one delta
Loops

If the loop opens
toward the pinky, it
is called an ulnar
loop (94%).

If the loop opens
toward the thumb, it
is called a radial loop
(6%).
Whorls

Whorls are divided into four groups: plain
(71%), central pocket loop (13%), double
loop (13%), and accidental (3%).
■ All whorl patterns
have one or more
cores and a
minimum of two
deltas.
Whorls



A plain whorl and a
central pocket loop have
at least one ridge that
makes a complete circuit.
If a line drawn between
the two deltas touches
the spiral, then it is a
plain whorl.
If the line does not touch
the spiral, it is a central
pocket loop whorl.
Whorls

The double loop is
made up of two
loops combined into
one fingerprint.

An accidental either
contains two or
more patterns, or is
a pattern not
covered by the
other categories.
Arches
Arches, the least common of the three
general patterns, are divided into two
distinct groups: plain arches (60%) and
tented arches (40%).
 Arches do not have type lines, deltas, or
cores.

Arches


The plain arch is formed
by ridges entering from
one side of the print,
rising and falling, and
exiting on the opposite
side (like a wave).
The tented arch is similar
to the plain arch except
that instead of rising
smoothly at the center,
there is a sharp upthrust,
or spike, or the ridges
meet at an angle that is
less than 90 degrees.
Henry Classification System





Worldwide acceptance in 1899
Allows for up to 1,024 primary groupings
First, the fingers are assigned a value from 1-10
Next, a numerical value is assigned to fingers
that contain a whorl pattern
Any fingers containing non-whorl patterns are
assigned the number 0.
Henry Classification System

The fingerprint record’s primary grouping
is determined by calculating a ratio:
Henry Classification System

If, for example, an individual has a fingerprint
record with a LWAALALWLA pattern series (RT
to LP), the corresponding classification ratio
would be 19:1
Henry Classification System
Approximately 25 percent of the population
falls into the 1/1 category; that is, all their
fingers have either loops or arches.
 A fingerprint classification system cannot in
itself unequivocally identify an individual; it
will merely provide the fingerprint examiner
with a number of candidates, all of whom
have an distinguishable set of prints in the
system’s file.

Fingerprints are unique



The probability for the existence of two identical
fingerprint patterns in the world’s population is
extremely small (1:6,000,000,000)
Besides theoretical calculations, of the millions
upon millions of individuals who have had their
prints classified, no two fingerprints have been
found to be identical.
The individuality of a fingerprint is not determined
by its general shape or pattern, but by the careful
study of its ridge characteristics, known as
minutiae.
Minutiae

It is the identity, number, and relative
location of these minutiae that imparts
individuality to a fingerprint.
There are as many as
150 minutiae on the
average finger, but
typically only 35-70 are
identifiable.
http://www.dkfz.de/tbi/projects/bmcv/images/iu_it246_04s_fingerprint1.jpg
Minutiae
After a three year study, it was determined
that “no valid basis exists for requiring a
predetermined minimum number of friction
ridge characters which must be present in
two impressions in order to establish
positive identification.”
 In a judicial proceeding, an expert must
demonstrate a point-by-point comparison
in order to prove the identity of an
individual.

AFIS
Automated Fingerprint Identification System



The heart of AFIS technology is the ability of a
computer to scan and digitally encode fingerprints
so that they can be subject to high-speed computer
processing.
AFIS aids in classifying and retrieving fingerprints
by converting the image of a fingerprint into digital
minutiae that contain data showing ridges at their
points of termination (ridge endings) and their
branching into two ridges (bifurcations).
When the search is complete (a computer can
make thousands of comparisons per second), the
computer produces a list of file prints that must be
examined by a trained fingerprint expert.
Visible Prints

Visible (patent) prints are made when
fingers touch a surface after the ridges
have been in contact with a colored
material such as blood, paint, grease, or
ink.
Latent Prints
Once the finger touches a surface, body
perspiration, oils and/or proteins present
on the finger ridges are transferred to that
surface, leaving an impression.
 Prints deposited in this manner are
invisible to the eye and are commonly
referred to as latent or invisible
fingerprints.

Plastic Prints

Plastic prints are ridge impressions left on
a soft material, such as putty, wax, soap,
or dust.
Detecting Prints

The best detection technique will depend on
 The
nature of the surface
 The presence of contaminants
 Environmental factors
 Age of the prints

There are three categories of techniques
that are used:
 Instrumental/Optical
 Physical
 Chemical
Instrumental Detection
Instrumental detection should always be
done first as they are non-destructive to
the print.
 These techniques are also useful in that
they may significantly improve the results
obtained by physical and chemical
methods.

Instrumental Detection
RUVIS (Reflected Ultraviolet Imaging
System)
 Can image latent and processed prints by
using intensified UV reflectance instead of
fluorescence
Instrumental Detection
MXRF (Micro-X-ray Fluorescence)
 Can image both visible and latent
fingerprints by detecting the presence of of
inorganic elements (Na, K, Cl) in print
residue resulting from perspiration
Physical Detection
Latent prints deposited on smooth, hard
and nonporous surfaces (e.g. glass,
mirror, tile, and painted wood) are
preferably developed by the application of
a powder
 Powders, available in a variety of colors,
can be applied with a brush or magnetic
wand, and adhere to perspiration and/or
body oils of the print

Physical Detection
Latent prints deposited on rough, more
flexible, nonporous surfaces (e.g. plastic,
vinyl, aluminum foil, leather, tape) are
preferably developed by cyanoacrylate
(Super Glue ® ) fuming
 Print development occurs when fumes
from the glue adhere to the print, usually
producing a white latent print

Physical Detection
Latent prints on porous surfaces (e.g.
paper, cloth, raw wood) can be
developed by iodine fuming
 Heating iodine crystals produces vapors
that combine with print oils to make them
visible.
 Iodine prints are not permanent and will
fade, making it necessary to photograph
the prints immediately.

Chemical Detection
Ninhydrin is used to develop latent prints
on porous surfaces (primarily paper).
 Reacts chemically with trace amounts of
amino acids present in print residue to
produce a purple-blue color
 Prints can be “fixed” by spraying with a
zinc chloride solution, changing the print
to an orange-brown color
 Can detect prints over 50 years old

Chemical Detection
DFO (1,8-diazafluoren-9-one) is similar to
ninhydrin in that it is used for primarily
paper, and it reacts with the amino acids in
print residue
 Fluoresces when illuminated with bluegreen light (ninhydrin does not)
 More sensitive and can develop up to 3x
more prints than ninhydrin

Chemical Detection
Physical Developer is similar to other
chemical methods in that it is used on
porous surfaces
 Reacts with lipids in print residue
 It is a silver nitrate-based reagent used to
develop prints when other chemical
methods are ineffective
 Can be used on wet samples

Sequence for Latent Print Development

Is the print on a porous or nonporous surface?
 If
nonporous…is surface smooth or rough? Can it
be transported easily?
If smooth – use powders
 If rough – use cyanoacrylate fuming
 If easy to transport – use cyanoacrylate fuming

 If
porous…is surface wet or dry?
If wet – use Physical Developer
 If dry – use iodine fuming  DFO  ninhydrin  PD

Transporting Prints
If the object is small enough to be
transported without destroying the print, it
should be preserved in its entirety
 Prints on large immovable objects that
have been developed with a powder can
best be preserved by “lifting” with a broad
adhesive tape
 The tape is placed on a properly labeled
card that provides a good background
contrast with the powder
