John R. Vanderkolk - National Criminal Justice Reference Service

C H A P T E R 9 Examination Process
There is much more to prints than the arrangement of
Galton points. The examiner must use knowledge and
understanding gained from training and experience to
make judgments about the features of the sources and
details in prints to reach a conclusion about the origin of
the print in question.
Cognitive science explains the processes of perception,
decision-making, and development of expertise. Research
in cognitive science is helping to explain how experienced
examiners differ from novices [Palmer, 1999; Busey and
Vanderkolk, 2005]. A philosophy of how examiners can
determine or exclude a source of a print must be established
for an examination method to be effective. Examiners
draw from many philosophies to develop a particular
examination method.
9.1.1 Philosophy of Uniqueness
Pattern formations in nature are never repeated in their
morphological structures (or, as the saying goes, “nature
never repeats itself”) [Kirk, 1963; McRoberts, 1996]. This
statement is supported and explained in part by biology,
chemistry, and physics, and through practice and experience
of observing natural patterns [Ball, 1999]. The morphogenesis
of friction skin and the many developmental
factors that influence the unique arrangement of friction
ridges prior to birth provide the fundamental explanation
of why volar skin is unique.
Basic print minutiae are defined and used in mathematical
formulas for traditional classification, statistical modeling,
and automated fingerprint identification systems
(AFIS). These formulas consider some of the variations in
friction ridge skin arrangements, but not all of the detail
that is present. In spite of these limitations, no model
and application has provided evidence that prints are not
unique. Instead, the study of pattern formations in nature,
and pattern formations in friction ridge skin in particular,
have determined the formations in friction ridge skin to be
unique. The friction ridge skin features of creases, furrows,
scars, cuts, and natural imperfections are also unique.
9.1.2 Philosophy of Persistency
The morphological surface structure of friction ridge skin is
persistent. Often, the friction ridge arrangement (ridge flow
and minutiae) has been described as permanent. However,
the cellular surface of the friction ridge skin is not permanent.
Surface cells are replaced on a regular basis. The
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competing forces of regenerating skin cells and the effort
of maintaining the form and function of the organ of skin
produces a persistent, not permanent, naturally patterned
surface with all of its minute and microscopic features. In
other words, the process strives to reproduce, but cannot
perfectly reproduce, the patterns of the preceding cells so
that the arrangements of replacement cells can follow the
form and function of the replaced cells. Microscopic variations
do occur. Aging of skin is an example of persistency;
although patterns in friction ridge skin are not perfectly
permanent, they are remarkably persistent over time.
For friction ridge skin to be valuable for the examination
of two prints, the unique features of ridges, creases, scars,
and imperfections in the skin that had been recorded as
details in two prints must be persistent between the two
occurrences when each print was made. Persistency is all
that is needed, not permanency.
9.1.3 Philosophy of Examination Logic
Deduction, induction, and abduction are three types of logic
[Burch, 2001; McKasson and Richards, 1998, pp 73-110]
an examiner can use to determine answers to questions
in friction ridge examinations. A simple explanation of logic
and inference could be found in the statements:
if A and B, therefore C
if B and C, therefore A
or
if A and C, therefore B
Replacing “A” with “Case”, “B” with “Rule” and “C” with
“Result”, the examiner can explain which logic is used.
9.1.3.1 Deductive Logic. “Case and Rule, therefore
Result” becomes “The two prints came from the same
source and individualization is possible because the
features of friction ridge skin are unique and persistent,
therefore, the details in the two sufficient prints agree.”
Deductive logic starts with and infers the general and ends
with the particular. Deductive logics infers that the particular
of the details between two prints agree if the examiner
knows the two sufficient prints did come from the same
source, or a specific area of skin, and that friction ridge skin
is unique and persistent. Deductive logic is used in training
examiners. The trainer and trainees know the two prints
came from the same source, the trainer and trainees know
the rule of uniqueness and persistency of friction ridge