Breaking NEWz you can UzE...
compiled by Jon Stimac
Solved Cold Case
GADSDEN COUNTY TIMES, FL
- Jan 12, 2007
...identified latent fingerprints found at the scene belong to
'Investigators tampered with Lotz evidence'
- Jan 10, 2007 ...US-based forensic scientist has accused
police investigators of "intentionally" fabricating fingerprint
Man Mistakenly Arrested In Tennessee, Sent To Maryland
EYEWITNESS NEWS, TN
- Jan 9,
2007 ...authorities realized that no one
ever ran his fingerprints...
Fingerprint May Link 'Clown' to Killing
CHICAGO SUN-TIMES, IL
- Jan 8, 2007
...newly revealed government evidence that a fingerprint of "Joey the
Clown" Lombardo links him to the slaying...
Recent CLPEX Posting Activity
containing new posts
Moderated by Steve Everist
10 years is enough fight for the McKie
clpexco Sun Jan 14, 2007 9:23 pm
Latent Print Openings in Fairfax County, Virginia
Bill Thu Jan 11, 2007 10:49 pm
Latent Print / Biometrics Examiner Openings
Lauren Cooney Thu Jan 11, 2007 4:09 pm
Ectodermal Dysplasia - Dermatopathia Pigmentosa Reticularis
Kasey Wertheim Thu Jan 11, 2007 1:56 pm
Point Of View: Point Counters and Pseudoscience
Charles Parker Wed Jan 10, 2007 4:00 pm
Oil Red O
Charles Parker Wed Jan 10, 2007 10:34 am
Evaluating latent prints
Larry Mazzola Wed Jan 10, 2007 1:51 am
Alternative digital method
Wayne Reutzel Tue Jan 09, 2007 10:43 pm
Red Tue Jan 09, 2007 10:34 pm
Do you use Individualization versus Identification?
Red.Sox.Fan Tue Jan 09, 2007 8:27 pm
Positions in Fingerprints
EmmaC Tue Jan 09, 2007 4:49 pm
LATENT PRINT SUPERVISOR - KING COUNTY SHERIFF’S OFFICE
Steve Everist Mon Jan 08, 2007 5:06 pm
Opportunities abound for latent print examiners
Kasey Wertheim Mon Jan 08, 2007 12:32 am
UPDATES ON CLPEX.com
2 new Smiley's were
added to the Smiley Files!
We heard from Mike Heintzman regarding the District of Oregon Daubert court
case, U.S. versus Hudson.
Craig Coppock brings us a look at what he defines as "Pattern Interference"
in latent print examination.
Pattern Interference in Latent
Friction Ridge Impressions
by Craig A. Coppock, CLPE
Regarding the Analysis phase of the ACE-V methodology, a
wide variety of distortion mechanisms must be understood. One particular
example of distortion is pattern interference. Interference patterns
result from multiple impressions of latent friction ridges superimposed on
one another. (Figure 1) The interference pattern of these impressions can
be from the combination of the same or different areas of friction skin. It
is very important to understand the various features of pattern
Figure 1. Two
overlapping latent print impressions of the same finger show a strong
interference pattern on the left side.
Interference features occur as the result of two or more overlying or
superimposed fingerprint impressions, or as the result of slight linear
and/or angular movement during the deposition of a single latent print
impression. In the latter, the flexibility of the epidermis under the
influence of non-perpendicular forces at the moment of latent deposition is
often the source of the non-alignment. In many aspects, latent print
impressions can be thought of as a static wave. These interference
patterns, also called moiré patterns, have several aspects that are related
to the basic physics of two-source wave type interference. The main
differences are that, in general, physical frequencies, such as water waves,
are repetitious generic amplitudes, whereas, each latent ridge contains
unique information in its static structure. In addition, along any
particular axis within a print impression, the frequency of the ridges, or
their relative spacing and direction, will vary to some degree due to the
unique shape of a fingerprint. Ultimately, we are concerned with how this
information changes at the constructive and destructive like interference
positions that result from non-aligned superimposed latent friction skin
impressions. What is found is that, unique information cannot be compounded
in a constructive nature. Not only would some information be lost to the
interference, some new non-relevant information would likely be gained.
Specifically, interference patterns are caused by like patterns types
occupying particular spatial relationships to one another. With overlapping
friction skin impressions, multiple interference patterns can be produced at
various angles. These visual interference geometries will be found at
different levels of prominence depending on the shape of each print and the
amount of relative difference or offset. If an overlapping print is just
slightly offset in a linear manner, few interference patterns are seen. If
an angular displacement is added, additional interference patterns will be
The following two examples of superimposed inked print impression show both
linear and angular rotational pattern features. In the left example of
Figure 2, the top print is offset to the right by about 1/2 ridge width.
The most notable interference is found in the vertical ridges. In the right
example of Figure 2, an additional counter clockwise rotation was added to
show the additional associated curved patterns. Note that with the
additional angular displacement in the right print, the interference pattern
left of the print’s core is not the same as the pattern found in the left
print even though they both had the same right linear displacement. As the
top print was rotated the ridges in this area changed their spatial
relationship. Also, on the right most print, note the epicenter just above
the core around which the rotation occurred. In most cases, a superimposed
print will not rotate so neatly around a center point. Since the ridges
above the epicenter are also semi-circular, the apparent distortion
is at a minimum as the ridges were superimposed in a more precise
alignment. Ridges perpendicular to the displacement often show the greatest
amount of interference.
Figure 2: LEFT: Overlapping ink prints with top
impression offset 1/2 ridge to the right. RIGHT: Same linear offset as
prints on left, yet with counter clockwise angular rotation added to top
The visual features where the patterns are at a point of focus are called a
node. A linear series of nodes along an axis are described as nodal
positions or locations. This nodal axis may be straight or curved.
Specifically, nodal positions are locations within the distortion area where
interference is at maximum and minimum levels. Anti-nodal positions
are where the interference is found to be at a maximum destructive level and
nodal positions are locations where the visual interference is
at a minimum,  or in some cases, an undisturbed state. See Figure 3.
Along the nodal axis, two ridges may precisely overly each other. As
previously noted, we would expect some loss of information when dealing with
unique friction ridges in such a relative state. As the particular physics
of two-wave source pattern interference is not entirely compatible with the
unique attributes of friction skin, and other individually unique types of
frequency sources such as shoe and tire impressions. Accordingly, we need
to understand that the areas of interference can only be described
accurately with the terms Nodal and Anti-Nodal. In our comparative
forensic science cases, these terms do not necessarily imply the value
or quality levels of the information contained within the friction ridges.
Figure 3: Example of minimum (Nodal) and maximum (Anti-Nodal) interference.
The offsets of the various impressions are most likely found in two
dimensions, and of varying degrees. As noted earlier, both
linear and angular displacements
must be considered, as well as the specific variability in the impression’s
frequency or ridges spacing. This can often be equivalent to our latent
print lateral and circular slippage.  This variability of ridge spacing
will be relevant to the specifics of the deposition itself, due again to the
flexibility of the epidermis and the variance of the substrate. Slight
changes in ridge spacing due to a compression or extension, will
accordingly, generate a specific interference pattern locally, and will be
visualized as a variation in both the nodal and anti-nodal axis. The direct
relationship between ridge frequencies and a difference in their expected
interference pattern appears to be mathematically proportional in symmetry,
meaning that a slight difference in displacement will yield a slight
modification in the axis of the interference pattern.
Figure 4: LEFT- Latent print with anti-nodal axis'
marked. MIDDLE- Exemplar. RIGHT- Recreation using two
superimposed exemplars. Linear and angular displacement indicated by
In figure 4 compare the anti-nodal axis locations on the latent print on the
left, with the interference patterns on the recreation print on the
right. The recreation print was made with two exemplars. The superimposed
second impression was offset and rotated several degrees counter clockwise.
Note that the left registration mark (in the upper right corner) is the
second impression. While the recreation composite is not a precise match,
it does illustrate the interference mechanism and principle.
It is important to understand that a superimposed print that is sufficiently
offset in its alignment with the first impression may not accurately
represent the spatial relationship of minutia of either print. This is
especially true when considering third level details. This combination can
create a new set of characteristics, or a combination of information from
each impression, that may or may not be visually separable. Also, it
is noted that the “ridges furthest from the epicenter of rotation (angular
displacement) … undergo a greater linear displacement than those nearer the
center.”  See figure 2. Thus, as related to fingerprint
individualization, the nodal and anti-nodal axis’ simply represents an
offset of ridges in relationship to the impression’s frequency or ridge
spacing, and not necessarily a division of the quality of information into
good and bad categories. Or in other words, the most apparent visual
interference at the anti-nodal locations may degrade the quality of the
information just as much as the nodal positions. In many cases the
seemingly clear areas along the nodal axis, are produced by different
ridges, or ridge sections overlying each other. The examiner will have to
critically analyze the impression to understand the composition of the
overlay, its degree of distortion, and subsequently the value of the
information available for comparison.
Figure 5: LEFT- Single impression. RIGHT-
Second impression superimposed one ridge to the left. Note that ending
ridges can become bifurcations and bifurcations are doubled.
In figure 5 the superimposed second impression is registered just one ridge
off down to the left. New information is created in the process, yet the
original characteristics are not entirely canceled out. In this case, Karen
Hare’s Proportional Analysis concept is beneficial in understanding
the true relationships of the information. 
The analysis stage of the ACE-V process is a fundamental inventory of
available informational components to be used in a comparison. This
information is analyzed for its quantitative and qualitative aspects, as
well as its specificity and relevance. With analysis being one of the most
difficult and variable aspects of the ACE-V, it is critical to fully
comprehend the specific makeup of a latent print’s distortion as this will,
in turn, help the examiner to better understand the value of the information
To create your own visual display of interference patterns in action,
scan one loop and one plain whorl pattern in Adobe Photoshop following the
simple guide below, repeating for the different pattern.
Adobe Photoshop, Scan a grayscale print at a good resolution.
600dpi or more.
the main layer. (right mouse click and select duplicate)
3. Turn off
the background layer for now.
4. Using the
magic wand, with a tolerance of about 50. Delete the background
from the new layer. All you want is a skeleton of a print.
5. With both
layers turned on, use your “move” tool and rotate layer features to
offset the two prints relative to each other. Note how the interference
patterns change relative to each prints linear and angular displacement.
Craig A. Coppock CLPE
1. Glenbrook South
Physics Teachers Home Page, Two point interference pattern.
Two Point interference patterns.
2. Wertheim, Pat
Analysis of Problem Latents & Ridgeology Comparison Techniques
(19 tools) Specifically: Lateral and Circular
3. Cowger, James: 1983
Friction Ridge Skin; Comparison and Identification of Fingerprints.
Elsevier, New York, p 187
4. Hare, Karen
(Midland Texas Police Department) Author of Proportional Analysis
(in comparative forensic science)
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