teacher background information
FSP07
Fingerprinting
Introduction to fingerprints and
fingerprinting
How are fingerprints formed?
During early embryonic development (four to
five weeks) there is swelling of (mesenchymal)
tissue on areas of the sole, palm and digits.
These areas are known as volar pads. The pads
stop growing at about 10 weeks of
development but the hand continues to grow.
The volar pads are then absorbed back into
the hand and as the pads shrink the skin folds
to produce the ridges of fingerprints. The first
ridges begin to appear at around 10 weeks.
Most human skin is quite smooth and covered
with hair follicles and oil glands. The finger,
palm and sole areas, however have no hair or
oil glands but instead have sweat pores and
friction ridges that take various forms and
shapes. The function of the friction ridges is to
increase grip and the sense of touch. The
study of friction ridge patterns is known as
dermatoglyphics.
Based on the pattern of pad absorption and
timing, various combinations of fingerprint can
occur:
The pattern of fingerprint ridges and pores is
different in each person; no two people have
the exact same pattern of ridges. It seems
that the general pattern of friction ridges may
be genetic, however the specific pattern or
fine detail is unique. Even for identical twins
this is true: they may have similar general
patterns but the fine details or ‘minutiae’
(my-new-shay) are different.

If ridges appear when the volar pads are
quite pronounced, the ridge pattern is a
whorl.
 If ridges appear when the volar pads are
less pronounced, the ridge pattern is a
loop.
 If ridges appear when the volar pads are
nearly absorbed, the ridge pattern is an
arch.
Timing and absorption during development is
genetically influenced; this is why identical
twins have similar ridge patterns. However,
within the general friction ridge pattern there
are many small variations known as minutiae.
The development of minutiae is a result of the
environment and external stresses and
pressures such as growth. So while identical
twins may have very close similarities in their
fingerprints, they do not have identical
fingerprints as they are subject to different
stresses and pressures while they are in the
womb.
Fingerprints are often used to identify or
eliminate suspects from a crime. These days,
with security being so important, the field of
biometrics (the process by which distinguishing
human anatomy is used for identification and
verification)
is
becoming
increasingly
important. Fingerprints are an important
element of biometrics.
As well as ridges, there are other elements
that make up a fingerprint. These are sweat
pores which can be located along the ridges.
Sweat pores are spaced almost evenly along
the ridges and they are responsible for
secretions which can sometimes leave fingerprints at the scene of a crime.
Forensic investigations: Fingerprinting (teacher information information)
FSP07 | revised May 2013 | © The University of Western Australia
page 1
Licensed for NEALS
What is a fingerprint?
First major case in the US
Fingerprints are the marks left behind when
someone touches an object with their finger.
There are three types of fingerprints that can
be left behind.
United States 1911. People vs Jennings
The first case in the US that involved
fingerprints as evidence was that of Thomas
Jennings. He was convicted of murder of Mr
Hiller, the owner of a home that Jennings
illegally entered.
1. An impression left in something soft (such
as butter, putty, soap or wet paint)
2. A print left by a finger that is covered in
something that is left behind such as dirt,
blood, paint or ink.
3. An invisible deposit left by secretions from
the skin. Everyone’s fingers have small
amounts of oil and perspiration which
come out of microscopic pores on the tiny
ridges of the fingerprints.
These
secretions also come out of different parts
of the body too.
Clarence Hiller always left a gas-light burning
at the head of the stairs near the door leading
to his daughter’s room. Shortly after 2am on a
Monday morning Mrs Hiller woke and noticed
that the light was out and roused Mr Hiller.
Hiller got up and encountered an intruder at
the head of the stairs. They struggled and both
fell which eventuated in Hiller being shot
twice. Hiller died from the gunshot wounds.
Hiller’s house had recently been painted. The
back veranda had been painted two days
earlier, on Saturday. Jennings entered the
house through a rear window in the kitchen,
which was close to the back veranda railing.
During the investigation of the crime scene,
police found the imprint of four fingers of a
left hand (which were recorded in the fresh
paint on the railing). The police removed the
railing so that it could be used as evidence.
Enlarged photographs of the prints were made.
Why are fingerprints used in forensics?
There are three basic principles about why
forensics scientists use fingerprints as
evidence:
1. After almost a century of fingerprint
existence, no two fingers have ever been
found
to
possess
identical
ridge
characteristics.
2. A fingerprint remains unchanged during a
persons’ lifetime. (Unless they are
involved in a accident which affects their
hands.)
3. Fingerprints have ridge characteristics that
allow for efficient classification and
examination.
Jennings
was
arrested
after
several
eyewitnesses identified him. A coincidence
during this case was that he had earlier had
been fingerprinted during a stint in prison in
1910. Jennings was again fingerprinted after
his arrest and when compared, the prints
produced a match.
History
The defendant argued that the evidence of the
comparison of his fingerprints to those found
on the railing was improperly admitted. The
accuracy of the photographs, the analysis
method, the taking of fingerprints or the
correctness of the photographic enlargement
was not questioned in court.
The FBI Identification Division started in 1924
with 8 million fingerprint files. Many of the
fingerprints were taken from criminals in
Leavenworth Prison.
By 2001 the FBI in the United States had well
over 250 million records from both criminals
and civilians. Civilian prints were taken from
government employees and applicants for
federal jobs.
Forensic investigations: Fingerprinting (teacher information information)
FSP07 | revised May 2013 | © The University of Western Australia
Various witnesses for the prosecution testified
about their expertise in regard to fingerprints.
This case established that there was a
scientific basis for the system of fingerprint
identification and that expert witnesses were
qualified to testify. Thomas Jennings was
sentenced to death and executed on February
16, 1912 for the murder of Clarence B Hiller.
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Fingerprint classification
Whorls
There are three main structures that make up
fingerprints. These are loops, whorls and
arches.
Whorls have a circular pattern and have at
least two deltas and a core. Whorls look a
little like target shapes or whirlpools – circles
within circles. Whorls make up 35% of patterns
seen in human fingerprints and can be subgrouped into four categories:
Loops
Loops are comprised of one or more ridges
entering from one side, curving, and then
going out the same side it entered. The ridges
in loops double back on themselves. All loops
have elements called a delta and a core. The
delta is a triangular area usually shaped like a
T-junction, while a core is the centre of the
pattern. About 65% of fingerprints have loops.
Loops can be divided into two groups:






Radial loops – these flow downward and
toward the radius (or the thumb side)
Ulnar loops – which flow toward the ulnar
(or the little finger side). The ulnar loop
is more common.
Plain whorls – which are either concentric
circles like a bull’s eye or spirals like a
wound spring.
Central pocket loop whorls – these
resemble a loop with a whorl at its end.
Double loop whorls – these occur when
two loops collide to produce an ‘S’-shaped
pattern.
Accidental loop whorls – these are slightly
different from other whorls and are
irregular.
Arches
Arches are the least common pattern making
up only 5% of all pattern types. Arches are
ridgelines that rise in the centre and create a
wave like pattern. The ridges enter from one
side and exit the other side with a rise in the
middle. They do not have a delta or a core and
can be broken into two sub-groups:
NOTE: you need to know which hand (right or
left) made the print before your can tell if it is
an ulnar or a radial loop.


Forensic investigations: Fingerprinting (teacher information information)
FSP07 | revised May 2013 | © The University of Western Australia
page 3
Plain arch – which has a gentle rise.
Tented arches - have a steeper rise than
plain arches.
The finer structures that make up fingerprints
are called minutiae. There are several types of
minutiae – these are displayed in the table
below. The dots found in the structures below
represent the pores on the ridges where sweat
is secreted.
Latent, patent or plastic prints
There are three general types of fingerprints
that can be left behind at a crime scene.
These types depend on how and where the
fingerprints were left. Some fingerprints are
easier to find than others. For example, a
print left in wet paint or on a greasy wall is
easier to find than one left with quite clean
hands on a garbage bag.
Fine structures – Minutiae (‘min-oo-shay’)
delta
These are the three types of prints forensic
scientists are likely to find:
ridge ending

Latent prints are invisible and cannot be
seen without special lighting or processing.
In latent fingerprints, the ridge structure
is reproduced on an object in sweat, or
other substances naturally present (or
added there by accident) on the fingers.
Although there are no oil secretions from
the fingers themselves we often have oils
on our hands from touching our hair and
face and this oil is enough to leave a print.

Patent prints are visible and occur when
substances such as blood, ink, paint,
grease or dirt on the fingers of the
perpetrator leave behind an easily seen
print. Visible or patent prints are visible
without any particular treatment

Plastic prints have a three-dimensional
quality and occur when the finger is
pressed into something that leaves an
indentation or impression print.
Soft
substances that patent prints may occur in
include wax, putty, soap, cold butter and
dust.
bifurcation
dot or island
hook
lake
bridge
An example of identifying minutiae in a
fingerprint is in the labelled picture below.
Simple detection techniques
used for developing
fingerprinting latent prints
There are two main ways that latent prints can
be detected; powders and chemical fuming.
Powders and dusting
Powders are used for detecting latent marks
on non-porous surfaces such as glass, plastic,
metal surfaces, glazed tiles and glossy paint.
The fine powder attaches to any greasy/oily
substances in the fingerprint deposit.
Powdering is only effective on quite fresh
marks as the mark dries out over time and
looses its stickiness. Black power (made from
carbon black or charcoal) and grey powder
(made from aluminium or titanium powder)
Forensic investigations: Fingerprinting (teacher information information)
FSP07 | revised May 2013 | © The University of Western Australia
page 4
are used most often. Police who dust at a
scene will use a powder that contrasts with
the object colour they are dusting on so that
prints are easier to see. Once the fingerprint
has been dusted, the latent impressions are
preserved as evidence either by photography
or by lifting powdered prints using special
sticky tape.
This is done in a fuming chamber and when
the iodine vapour combines with oils in the
latent print a brownish print is produced.
This sort of print does fade quickly though,
so photographs must be taken straight
away or it must be fixed by spraying the
print with a solution of starch and water.
The starch and water will preserve the
print for several weeks or months.
If you wish to try dusting with your students
you will find that cocoa powder or talcum
powder work well. Fine powders work best.
3. Ninhydrin. Ninhydrin (triketohydridene
hydrate) has been used for years to reveal
latent prints and it is an important and
regularly used technique today. The
evidence that the latent print is meant to
be on is dipped in or sprayed with
ninhydrin solution. This solution reacts
with the oils and proteins in the print.
This process is extremely slow and it may
take several hours for the print to appear
as a purple-blue colour. Heating the
object to around 26 to 38° C will speed up
the process.
Chemical fuming: using chemistry to
expose prints
Latent prints can also be developed using
chemicals to expose prints. This is called
chemical fuming.
Chemical fuming is when the surface with
suspected prints is exposed to chemical fumes.
When fingerprints are difficult to see or if
forensic scientists are not sure if fingerprints
are present, they use this technique to
‘process’ fingerprints and make them visible.
Ninhydrin is used on porous surfaces such
as paper, cardboard, fabrics and untreated
wood. As protein molecules are quite
stable, old latent marks and prints can be
developed with ninhydrin.
1. Cyanoacrylate vapour. More commonly
known by its trade name – Super Glue
(which is 98% cyanoacrylate). This is an
extremely useful forensic tool. When
heated and mixed with sodium hydroxide
(another common household chemical),
cyanoacrylate releases vapours that bind
to amino acids. There are amino acids
present in print residue, so voila, when
they bind a hard, white latent print is left
behind.
The
print
can
then
be
photographed as is, or treated with a
florescent dye that will make the print
glow under UV light.
4. Silver nitrate. Silver nitrate is a
component that is used in black and white
photographic film. This process works to
produce a black or reddish brown print
when viewed under ultra violet (UV) light.
Sweat is often a component found in
latent prints. Sweat contains salts, one of
which is sodium chloride (like the salt you
put on your dinner). When investigators
expose the latent print to silver nitrate,
the chloride in the salt reacts with the
silver nitrate to form a new compound
called silver chloride. This colourless
compound will develop and become visible
when exposed to UV light.
The evidence that is to be checked for
fingerprints is often exposed to the vapour
in something called a fuming chamber.
This can be done at the crime scene in a
fuming box, but these days police
frequently use hand held wands. These
gadgets heat a small cartridge of
cyanoacrylate mixed with florescent dye
which can be directed at latent prints at a
crime scene. When prints react with the
cyanoacrylate, they are also fixed at the
same time with florescent dye making the
process much faster and easier.
Super Glue vapour works well on surfaces
such as glass, plastics and metal objects
2. Iodine fuming. When heated the solid
crystals of iodine release iodine vapours.
Forensic investigations: Fingerprinting (teacher information information)
FSP07 | revised May 2013 | © The University of Western Australia
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Analysis of fingerprints
Interesting Information
The assessor must determine if the recovered
fingerprint is clear enough to enable a full
analysis. If so, there are three steps that the
scientists must follow to be able to accurately
assess the print. The print is always
photographed.
It is possible to collect DNA from non-blood
latent fingerprints. Skin cells are continuously
being shed and can be deposited in a
fingerprint.
There a many more techniques used to detect
latent fingerprints. Among them are: vacuum
metal deposition, small particle reagent,
gentian violet and use of luminescence and
fluorescence.
Step 1 – does not require magnification
Assess the overall pattern of the friction
ridges. Whorl, loop or arch.
Latent fingerprints can be detected on human
skin. It is however a very difficult surface to
get prints off mainly because the same
secretory compounds that are in the
fingerprints are also naturally on the skin. If a
print is less than a few hours old it can be
possible.
Step 2 – requires x5 to x10 magnification
Major ridge pattern deviations or minutiae or
points of identification are established: ridge
endings, bifurcations and dots (and variations
of these basic patterns). Features such as
scars, creases etc are also included.
All primates also have friction ridges on their
hands and feet. Some new world monkeys also
have friction ridges on their tails.
Step 3 – higher magnification
Details such as the alignment or shape of
ridges, pore shape and position.
Fingerprints are then compared between the
unknown mark (the fingerprint found at the
scene) and a known print (a print found in
police records or collected from a suspect).
Cleaning up the print using
digital techniques
More often than not a print or a partial print
found at the scene of a crime is unclear. It is
uncommon to get a perfect print! The minute
details of a print may be fuzzy, missing or
difficult to see. With the development of
digital technology, the problems with
fingerprints can be solved more easily than
before. Prints can be scanned into a computer
and then transferred into one of many
computer programs. These programs can
enhance, improve, and clean up the computer
generated image of the print. By changing the
light, clarity, contrast and background
patterns electronically, certain details of the
print can become more obvious giving the
investigators more clues than previously
available, providing more accurate evidence
and also speeding up the matching process.
Forensic investigations: Fingerprinting (teacher information information)
FSP07 | revised May 2013 | © The University of Western Australia
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