Transcript Notes on Fingerprinting

Click here to view the
Henry Classification System
Formation of Fingerprints
 An animal’s external tissue (skin) consists of (a) an inner
dermis and (b) an outer epidermis.
 The creation of fingerprints occurs in a special layer (the
basal layer) in the epidermis where new skin cells are
produced.
 Fingerprints probably begin forming at the start of the 10th
week of pregnancy.
 Because the basal layer grows faster than the others, it
collapses, forming intricate shapes.
Forensic Science: Fundamentals
& Investigations, Chapter 6
2
Characteristics of Fingerprints
 There are 3 general fingerprint distinctions:
ARCH
About 5%
population
Forensic Science: Fundamentals
& Investigations, Chapter 6
3
WHORL
About 30%
LOOP
About 65%
of the
Type of Prints
Forensic Science: Fundamentals
& Investigations, Chapter 6
4
wikipedia.org
Loops- depends on which hand it is found on makes it
either:
Radial
Ulnar
 Radial loops start on the
 Ulnar loops start on the
thumb-side of the finger, the
side closer to the radius bone
pinky-side of the finger, the
side closer to the ulna, the
lower arm bone.
Arches
Plain Arches
Tented Arches
 If you compare the two images, plain arch and tented arch,
you can see that while the plain arch tends to flow rather
easily through the pattern with no significant changes, the
tented arch does make a significant change and does not
have the same "easy" flow that the plain arch does. The
technical definition is that a tented arch has a "significant
upthrust" where a plain arch does not.
http://www.policensw.com/info/fingerprints/finger07.html
Whorls
DOUBLE LOOP
PLAIN
CENTRAL
POCKET
ACCIDENTAL
 Between 25 and 35 per cent of the patterns encountered consist of
whorls. In a whorl, some of the ridges make a turn through at least one
circuit. Any fingerprint pattern which contains 2 or more delta's will be
a whorl pattern. In the scheme of classification you can make the
assumption that if a pattern contains no delta's then it is an arch, if it
contains one (and only one) delta it will be a loop and if it contains 2 or
more it will always be a whorl. If a pattern does contain more than 2
delta's it will always be an accidental whorl.
Minutiae
Characteristics of Fingerprints
 Forensic examiners look for the presence of a core (the
center of a whorl or loop) and deltas (triangular regions
near a loop).
 A ridge count is another characteristic that distinguishes
one fingerprint from another. The count is made from the
center of the core to the edge of the delta.
Forensic Science: Fundamentals
& Investigations, Chapter 6
9
Deltas
Forensic Science: Fundamentals
& Investigations, Chapter 6
10







A. ending ridge
B.bifurcation (fork)
C. eye (enclosure or island)
D. Dot
E. Island ridge
F. Spur
G. Bridge
Forensic Science: Fundamentals
& Investigations, Chapter 6
11
Types of Fingerprints
There are 3 types of prints that
investigators look for at crime scenes:
Patent fingerprints are visible prints transferred
onto smooth surfaces by blood or other liquids.
2. Plastic fingerprints are indentations left in soft
materials such as clay or wax.
3. Latent fingerprints are not visible but made so
by dusting with powders or the use of chemicals.
1.
Forensic Science: Fundamentals
& Investigations, Chapter 6
12
wikipedia.org
Collection with Powders
Magnetic Powders
Dusting Powders
 Powders may be applied with a fingerprint
brush, a brush with extremely fine fibers
designed to hold powder, and deposit it
gently on the fingerprint to be revealed,
without rubbing away the often delicate
residue of the fingerprint itself. They may
also be applied by blowing the powder
across the fingerprint, or by pouring the
powder onto the print, and then blowing
away the excess.
 Magnetic powders are also used,
where a fine magnetic powder is
held by a magnetic applicator,
which may then be gently moved
across the fingerprint. As no
bristles touch the surface, this
often damages the print less than
other methods of developing the
print.
Fingerprint powders have various formulations, and the appropriate powder must be
used on the appropriate surface. For example, dark coloured powders will show up a
fingerprint far better on a light surface.
Cyanoacrylate (Superglue)Fuming
Cyanoacrylate fuming is a widely used forensic tool for
the development of latent fingerprints, however the
mechanistic details of the reaction between the
fingerprint residue and the cyanoacrylate vapor are not
well understood. Here the polymerization of ethylcyanoacrylate vapor by sodium lactate or alanine
solutions, two of the major components in fingerprint
residue, has been examined by monitoring the time
dependence of the mass uptake and resultant polymer
molecular weight characteristics. This data provides
insight into the molecular level actions in the efficient
development of latent fingerprints by superglue fuming.
The results show that the carboxylate moiety is the
primary initiator of the polymerization process and that
a basic environment inhibits chain termination while an
acidic environment promotes it. The results also
indicate that water cannot be the primary initiator in
this forensic technique.
To See a Video, Click Here
http://www3.interscience.wiley.com/journal/118519289/abstract?CRETRY=1&SRETRY=0 `
Iodine Fuming
 The iodine fuming technique has historically been
recognized as one of the earliest techniques available to the
investigator for developing latent prints. Prior to the
introduction of chemical methods, such as ninhydrin,
iodine fuming was a preferred and recommended method
to be used on paper products.
Iodine fumes are sensitive to different latent residues than other
methods. It is possible that latent prints that would have been
developed by iodine fumes will not be developed by other means,
whose application will then destroy the residue needed for iodine
development. When the nature of surface is questionable as to a
particular technique, or sequence of techniques, iodine fuming
should definitely be considered. That was the case some years
involving a piece of surgical tape.
To read more, click here
Ninhydrin Spray
 Ninhydrin, an amino acid reagent, may be applied to
porous surfaces in a variety of solutions to develop latent
finger and palm prints. The choice of application depends
on the surface being processed, the expertise of the
examiner, and the equipment and supplies available.
…Choosing the correct formula and method in any given
situation will maximize the chances of success while
minimizing the hazards, both to the examiner and the
evidence.
http://www.geocities.com/cfpdlab/ninhydri.htm
Fingerprint Forensic FAQs
 How are latent fingerprints collected?
Forensic Science: Fundamentals
& Investigations, Chapter 6
17