T H E
D E T A I L
Monday, February 18, 2002
Good morning via the "Detail," a weekly e-mail newsletter that greets latent print examiners around the globe every Monday morning. The purpose of the Detail is to help keep you informed of the current state of affairs in the latent print community, to provide an avenue to circulate original fingerprint-related articles, and to announce important events as they happen in our field.
Last week, Steve Howard gave us a look at overlapping prints and his thoughts on some limitations when reporting conclusions. If you didn't get a chance to read those thoughts, you may do so at the Detail Archives.
This week, Mary Beeton brings us our Weekly Detail, and elaborates on the practical application of the methodology of fingerprint examination.
Friction Ridge Identification Process – Proposed Scientific Methodology
by Mary Beeton
The friction skin identification process involves the application of an identification philosophy and scientific methodology in order to determine whether or not an ‘unknown friction ridge impression’ (herein referred to as a latent) originated from the same source as a ‘known inked print’ (herein referred to as a print) to the exclusion of all others. The following deals primarily with an introduction to the scientific methodology portion of the identification process.
note that the following is primarily a compilation of ideas and protocols
developed by David Ashbaugh, Pat Wertheim and Christophe Champod PhD. with a few
modifications based on my own personal preferences.
Extensive detail, especially with respect to the ‘examination of the
latent’, has not been provided since the purpose of this document is to
provide a general approach to a scientific methodology as part of the overall
identification process. Certain
aspects of this proposed scientific methodology may or may not be applicable
depending on the level of examiner expertise and each particular ‘latent to
print’ identification process case.
identification philosophy “is a guide or explanation of how friction ridge
quantitative-qualitative analysis is transformed into an opinion of
individuality. It describes the
friction ridge formations used during analysis and establishes parameters as to
how much knowledge one must have to perform such a function.
The philosophy of friction ridge identification can be paraphrased with
the following statement: Friction
ridge identification is established through the agreement of friction ridge
formations, in sequence, having sufficient uniqueness to individualize.”
Ashbaugh, Quantitative-Qualitative Friction Ridge Analysis, pg.85 May 1999
A.C.E.-V. (Analysis Comparison Evaluation and Verification) is a common approach to applying a scientific methodology in the friction ridge identification process. The “five-step formula” proposed by Pat A. Wertheim, C.L.P.E. is a different way of interpreting A.C.E.. According to Mr. Wertheim it is “an alternative way of explaining the same mental process” (as with A.C.E.). “Some examiners find the five-step formula easier to understand, easier to apply, and more precise in its explanation to a layperson.”
The ‘modified’ five-step identification formula is as follows:
1) Examination of the Latent.
Development of Propositions (or hypotheses) to be addressed.
‘Latent to Print’ Experimentation.
Formation of a Tentative Conclusion.
Let’s look at each step in
Examination of the Latent
This step is comparable to the ‘analysis’ of the latent as in the A.C.E. method. David Ashbaugh describes the analysis stage as “intelligence gathering”.
Quite often certain information, such as
types of distortion present, are not always obvious in the latent at this stage
and may be revealed later on in the friction ridge identification process.
is a thorough ‘examination of the latent’ important?
Don’t be fooled by first
impressions! (pun intended) Even
though some latents appear to be of extremely good quality containing clearly
visible second level detail in large quantities and possibly third level
detail - a standard but thorough analysis of the latent may reveal certain
not-so-obvious factors. These
factors may have a huge impact on the examiner’s ‘approach’ to the
comparison of the latent to the print and eventually his/her evaluation and
conclusion of ident or non-ident. Latent
print examiners beware! Everything
isn’t always as it seems!
When the opposite is true…obvious
distortion is present throughout the latent, a through examination will help the
examiner reaffirm in his/her mind what is a friction ridge formation and what is
not. If the examiner concludes that
certain areas of the latent are affected by or actually caused by distortion,
the ‘examination of the latent’ process will ensure that the expert has the
ability to communicate why the latent has a certain appearance. This is
especially true for more difficult and complex latents.
Ashbaugh suggests completing the analysis from bottom of the latent to the top
(in three dimensional terms). In
other words, start with the substrate (surface upon which the print is
deposited); then proceed to look at signs in the latent that may indicate the
type of matrix (substance that is transferred from the source to the substrate)
which resulted in the creation of the actual latent; next consider the
development medium used to enhance the latent; then consider noticeable
indicators of how the latent was physically transferred onto the substrate
(pressure-related distortion, flexibility of skin, handling of substrate).
Lastly consider any ‘red flags’ or any other types of distortion that
decrease the clarity and reliability of the information provided by the
‘apparent’ friction ridge formations or features.
Clarity and tolerance levels are considered before proceeding with major
ridge path configuration (2nd level detail) and intrinsic ridge
formations (3rd level detail) and anatomical aspects.
matter what order you choose to complete the examination of the latent, it is
important to follow the same order each and every time.
Overlooking one or more steps in the examination of the latent could
result in an inaccurate assessment and therefore impact the remaining steps in
the identification process. Even
with apparently uncomplicated latents, the steps should be followed as a matter
of routine. The more time spent really analyzing latents, the more adept
you will become at recognizing significant factors which will contribute to your
Suggested Protocol for the
Examination of the Latent:
question one of the first things considered when analyzing a latent print is
clarity. As latent print examiners
we often look at so many low clarity impressions that when a high clarity print
comes along it is much appreciated. We
must realize though that good clarity i.e. well defined ridge path, edges,
incipient ridges and so on, comes to us with the knowledge that our tolerance
for any discrepancies between the latent and the print should be at its lowest.
If the lack of clarity, is accompanied by a lack of quantity of
friction ridge path configurations (2nd level detail) or visible 3rd
level detail, the examiner may need to also rely on alternate information in the
print such as creases, incipient ridges or scars in order to make a positive
identification. In this situation
our tolerance for distortion may be higher but ‘sufficient detail’ must
include a greater quantity of information than if the latent print was clear.
The quality of information (lack of, or abundance of, clarity in the latent) is
an immediate caution indicator as to the ‘significance’ of the information
contained within the latent. The
quality and quantity of information in the latent determines whether a
positive identification can be effected.
such as ‘double taps’ or ‘layered’ fingerprints, colour (tonal)
reversals, ridge inconsistencies, light and dark areas, sudden directional
change in ridge flow, differences in ridge width throughout the impression and
lines through pattern area caused by substrate (e.g. knife serrations) etc.
The examiner may give certain areas of the latent less significance if
any at all in the identification process because of the presence of ‘red
is important to know what development process was used to enhance the latent.
Each development medium, whether it is black or white powder, ninhydrin,
cyanoacrylate, has its own catalyst (substance with which the development medium
reacts) and signature (appearance it takes on after reacting with the catalyst).
is most evident on latents found on flexible surfaces such as plastic or
surfaces that are uneven in texture or colour such as cheques or documents.
is the actual substance deposited by the friction ridges e.g. sweat that may be
contaminated with oil and dirt. Are
characteristics of a ‘wet’ fingerprint present?
David Ashbaugh describes ‘wet’ prints as prints resulting from
“Water adhering to the friction ridges between the pores at the time of
contact with the substrate tends to be pressed to the sides of the ridge next to
the furrows. This often creates
thin matrix lines along each side of the ridge next to the furrows.
The resulting print structure has ridge breaks between the pores giving
the ridge a dot like appearance. In
most cases wet print ridges will appear broken and should only be compared as if
they were solid ridges or as second level detail.”
Also, is the distortion consistent throughout?
consider Physical Transfer Distortion to be any type of distortion caused as a
result of the actual physical motion that took place as the matrix was
transferred onto the substrate. This
could be evident in ‘thick’ ridges caused by downward pressure of the finger
or palm. Lateral or downward swipes
originating from the ridge detail area could be indicative of directional
movement of the finger or palm shortly after it makes first contact with the
substrate. A common example of this
would be vertical or horizontal swipes across a surface such as a window being
forced open. Flexibility of skin
causes physical transfer distortion whether there has been normal handling of
items as in grasping and holding movements, or simply anytime the skin comes in
contact with an item. In other
words, theoretically every latent or print has some form of P.T.D.
location and direction of the latent on the substrate can provide valuable clues
as to the correct orientation of the latent – especially if the pattern is not
orientation of the latent will certainly make the experimentation (comparison)
process easier. If there is a
cluster of prints, it may be possible to determine from which finger the print
may have originated.
for Selecting a ‘Target’ in the Latent:
near a ‘Focal Point’.
On one of
the ‘type’ lines (diverging ridges of the triradius area).
innermost recurving or recircuiting ridge.
the outer parameters or ‘defined area’ containing the target.
‘occasional’ features. For example, creases and wrinkles, incipient ridges,
permanent scars, temporary damage, open fields, warts, circular ridge and
which finger or palm.
the target. (The more ‘creative’ the name the better for remembering.)
“A thorough analysis should be accompanied by the taking of detailed notes describing the latent print. Notes should make reference to all observed distortion factors. Notes may also include reference to the level of clarity present in the print. One might actually draw the target, both as an aid in its memorization and as a part of the description of the latent. On occasion, one may even choose to physically follow or trace the ridges completely throughout the print and draw a representation of the entire latent in the notes. This type of demonstrable analysis lends credence to any subsequent identification.” Pat A. Wertheim, C.L.P.E., Scientific Comparison and Identification of Fingerprint Evidence, 2000
Development of Propositions to be addressed.
are three possible propositions (or hypotheses) to address:
latent was made by the ‘person of interest’ who provided the inked prints.
Result = Identification
The latent was left by another person other than the ‘person of
Result = Non-Identification
Insufficient information in the latent or known print or both to conclude
as to the source of
Result = Inconclusive
‘Latent to Print’ Experimentation
in the comparison step of A.C.E., experimentation involves going back and forth
between the latent and the print, first finding features in the latent (assuming
it’s the most unclear print), then examining the known print for the same
formations within tolerance.
Guidelines for Experimentation (Comparing the Latent with the Inked Print):
point, examination (analysis) of the latent is complete and its “full detail
is fixed in the mind of the expert and all [obvious] factors of distortions have
been considered”. Pat
take any preconceived thoughts or expectations into the comparison.
Don’t ever “get married” to a specific digit determination or palm
often the latent is compared to the known print – this is assuming that the
latent contains less information and detail than the known print.
The experimentation process should be carried out such that the poorest
quality print is compared to the best quality print.
known prints available i.e. rolled, flats and palms.
Be in an
‘alert’ state of mind.
for ‘unaccountable differences’.
any ‘formation’ or ‘feature’ that is not understood but, at the same
time, keep an awareness of your tolerances.
As these exclusions increase in number your tolerance for them must
decrease to the point that too many exclusions must result in a non-ident.
use all three levels of detail if possible – NEVER use only one and ignore
other features. It is not valid to
use some but not all of the obvious information present.
Experimentation could begin at Level 1 or Level 2 or Level 3 depending on
the total information available in the latent and print.
1 - The ‘overall’
pattern is discernable in the latent. Other
“overall type” features such as the presence of incipients, creases, scars
may be evident without any magnification.
there agreement with the known print within tolerance?
Yes – Experimentation continues…
If No - Experimentation ends. Results
2 – Observation of 2nd
level detail commonly referred to as “points” or “major ridge path
1) Locate the target* in
known print. (*Refer back to the examination process if necessary for a
detailed explanation of choosing a target.)
In same location?
Apply outer parameters.
Search target only once, then shift to a different target.
As far from first target as possible
3 targets or 10 minutes
move on to a different latent
2) Target must be within
tolerance. Clarity of the prints will dictate your level of tolerance.
“It is an easy task to understand and to account for the differences in
appearance between a print resulting from a light touch and a print resulting
from a heavy touch.” If this were
the only difference between the latent and the known print, this difference
would be explainable and said to be within tolerance.
If the clarity of the latent is good, a target of a small enclosure in
the latent where a short ridge is located on the known print would be considered
out of tolerance at level two.
3) Search for additional
features i.e. bifurcations, ridge endings, dots, enclosures, short ridges, ridge
4) If possible, count
the ridges from the triradius to the centre of core and compare with known
print. Ridge count must be within
”Run the Ridges”
Establish the route of each
friction ridge. This helps to
‘bring out’ additional friction ridge formations that may have been missed
previously. Ashbaugh explains that,
“Independent ridge paths should be discernable; their flow should be in
concert “. Unless 3rd
level detail is visible, ridge breaks should be treated as if the ridge is
continual. This is invaluable
information for any latent print examiner!
”Run the Furrows”
Establish the route of the
furrows and determine whether or not they are in agreement with the ridges.
there agreement with the known print within tolerance?
YES – Experimentation can continue on to Level 3.
If NO – Experimentation stops.
Result = Non-Ident
Level 3 - Observation of shapes within and along the ridges on close inspection
1) Look for intrinsic
ridge shapes, pore shapes and relative one-to-another pore locations if
visible (3rd level detail).
there agreement with the known print within tolerance?
YES – Experimentation is complete.
If NO – Experimentation ends.
Results = Non-Ident
Formation of a Tentative Conclusion
If you have found substantial agreement of friction ridge formations in sequence between the latent and the print it is now possible to formulate a “tentative conclusion” that the latent came from the same source as the known print. As Pat Wertheim explains, “As most experienced latent print examiners will recognize, the comparison does not cease at the first instant the expert reaches a conclusion. In practice, the comparison always continues past this point. The conclusion at the very first is, indeed, tentative.”
Testing the Conclusion
agreement of friction ridge formations in sequence has been established at this
point in the identification process, however, using Pat Wertheim’s words,
“The examiner continues to search for additional features until it is reliably
proven that each time a new feature is found in the latent print, a
corresponding feature will exist in the inked print. The continuing comparison, testing the conclusion, is
the final step in the [identification] process.
[Proposition ‘A’] is said to be proven and the identification
finalized when the examiner has established “reliable predictability” in the
relationship of [friction ridge formations] as they exist in the unknown and
order to address a possible courtroom scenario question:
“At what exact point did you know that you had an identification?”…
the answer using this modified five-step identification formula would be:
the moment in time that it was reliably predictable that each isolated feature I
selected from the crime scene print could be readily located and found to be
sequentially in agreement with the inked print.”
– Final Step in a Complete Scientific Methodology
speaking, verification is not part of the identification process.
The identification itself takes place in the mind of the examiner making
the comparison. Verification is the
identification process repeated in someone else’s mind.”
second Latent Print Examiner completes a verification of the first Latent Print
Examiner’s findings. This step is
not to be treated lightly and is an integral part in making fingerprint
identification a ‘science’. Verification
also ensures objectivity in the comparison of the unknown to the known print.
It is an important final step in the entire friction ridge identification
or ‘non-identification’ process.
is a form of peer review and is part of most sciences.
Many organizations erroneously use verification as a method of protecting
against errors in place of adequate training.
While verification may prevent the occasional error, its purpose is to
verify process and objectivity as opposed to only check results.
It is also an excellent vehicle for training.”
other words, the person who completes the verification should begin at Step 1 -
‘Latent to Print’ Examination.
on this approach to the friction ridge identification process using a different
way of interpreting A.C.E.-V. are welcomed and appreciated.
I would like to take this opportunity to thank Terry Smith of the Niagara
Regional Police Service, Ontario, Canada and Kasey Wertheim for their
contributions and encouragement.
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Have a GREAT week!