FSP 07
fing erprinting
Teacher Background Information
Introduction to fingerprints
and fingerprinting
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.
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.
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.
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.
Based on the pattern of pad absorption and timing,
various combinations of fingerprint can occur:
• 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.
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.
FSP 07
fing erprinting
Teacher Background Information
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
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.
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.
History
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.
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.
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.
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.
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.
Various witnesses for the prosecution testified about
their expertise in regard to fingerprints.
FSP 07
fing erprinting
Teacher Background Information
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.
Fingerprint classification
There are three main structures that make up
fingerprints. These are loops, whorls and arches.
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:
Whorls
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 sub-grouped into four categories:
• 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.
Whorls
• 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.
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:
Loops
• Plain arch – which has a gentle rise.
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.
Delta
Core
• Tented arches - have a steeper
rise than plain arches.
Arch
FSP 07
fing erprinting
Teacher Background Information
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.
Fine structures – Minutiae (min oo shay)
Delta
Ridge ending
Bifurcation
Dot or island
Hook
Lake
Bridge
An example of identifying minutiae in a fingerprint is
in the labelled picture below.
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.
These are the three types of prints forensic scientists
are likely to find:
• 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.
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
FSP 07
fing erprinting
Teacher Background Information
and looses its stickiness. Black power (made from
carbon black or charcoal) and grey powder (made
from aluminium or titanium powder) 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.
If you wish to try dusting with your students you will
find that cocoa powder or talcum powder work well.
Fine powders work best.
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.
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.
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. 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.
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.
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.
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.
FSP 07
fing erprinting
Teacher Background Information
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.
Step 1 – does not require magnification
Assess the overall pattern of the friction ridges.
Whorl, loop or arch.
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.
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.
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.
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.
All primates also have friction ridges on their hands
and feet. Some new world monkeys also have
friction ridges on their tails.