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Dissimilarities and Distortion (The following paper was presented as a poster presentation at the 1993 Forensic Symposium on Latent Prints hosted by the Federal Bureau of Investigation in Quantico, Virginia)
By WILLIAM F. LEO C.L.P.E. Confusion exists among latent print examiners who interchange the concept of dissimilarities with the concept of distortion. Literature on friction skin identification rarely addresses this subject in any detail. As a result of this confusion, there is a loss of credibility within the criminal justice system when latent print examiners are unable to explain these concepts and defend their conclusions on the witness stand. Just as similarities are used to establish identity, dissimilarities establish the fact that two prints are not the same. Thus the definition of dissimilar: being absent of similarity -- of not being the same -- different.
This definition differs from that of distortion which is defined as: to
modify
Distortion, however is commonly found in both latent and exemplar prints Dissimilarities occur in prints that are not the same. That is why during a latent print examiner's early training they are taught that if a print has a dissimilarity, you do not have an identification. This information has also been documented in a number of classic texts on friction skin identification including Moenssens (1972) and Olsen (1978).
Unfortunately, this concept has been misinterpreted and over simplified
to the point that some latent print examiners state that regardless of
similarities, if a dissimilarity is found the identification is voided.
This incorrect concept was published by Fox and Cunningham (1973). This
problem is compounded by the use of confusing and ambiguous terminology
to describe these two concepts, such as the “explainable dissimilarity”
and the “unexplainable The concept that a dissimilarity could exist regardless of how many similarities are found cannot be valid. If this were possible, then there would always be a possibility of a dissimilarity and a conclusive identification could never be made. Dissimilarity and distortion are not interchangeable terms and the two concepts should not be confused. Dissimilarities only occur in prints that are not the same. Once sufficient matching characteristics are found to establish identity, dissimilarities cannot and will not be found. This has been noted by Clements (1987), Cowger (1983), and the FBI (1969). Distortion alters the appearance of prints, sometimes interfering with the comparison, however distortion is common in all prints regardless of whether or not they are the same. It is important that latent print examiners be trained, and each fully understand the concepts of similarities and dissimilarities, and how dissimilarities differ from distortion, prior to giving testimony as expert witnesses in the field of friction skin identification.
References: Cowger, James, Friction Ridge Skin, Elsevier, New York, 1983, P. 176.
Federal Bureau of Investigation, Law Enforcement Bulletin, “Fingerprints Do Not Lie”, September 1969. Fox, Richard and Cunningham, Carl, Crime Scene Search and Physical Evidence Handbook, U.S. Department of Justice, 1973, p. 48. Moenssens, Andre, Fingerprint Techniques, Clinton, Philadelphia, Pa., 1971, pp. 260--262. Olsen, Robert, Scott's Fingerprint Mechanics, Thomas, Springfield, Ill., 1978, p. 29.
Notes: Clements notes that if there is sufficient matching characteristics any dissimilarities would be explainable. Cowger states that “determination of identity is based on the presence of similarities, not the absence of dissimilarities”. Both Clements and Cowger are referring to distortion which may be present or appear as dissimilarities. However, both acknowledge that once sufficient matching characteristics are found to establish identity, regardless of any distortion that may be present, that the identification is valid.
(Editor --— This paper was well received and applauded by many attendees
at the symposium.
This article was reprinted in “THE PRINT” 10(5), April 1994, pp 1-2 |