Q.  What does the latent print expert offer?  

A.  The expert offers interpretations, based upon scientific principals, that are reproducible.

The field of latent print identification is well established and a consensus by experienced latent print examiners is readily obtained on “makes” and “eliminations.”  The two scientific premises upon which latent print comparison is based --— friction ridges on the human body remain the same through--out the life of an individual and no two fingerprints are identical --— are easily verified by observation and have been well documented.  The only areas really open for interpretation are: a) the number of characteristics that are necessary to uniquely identify a given print and b) interpretation of a developed latent (i.e.: what characteristics are observable).  Thus the “opinions” offered by latent print experts are not mere “opinions;” but are more an interpretation or conclusion by trained individuals after conducting an examination employing scientific principals.

BASIS  OF  FORENSIC
COMPARISON OPINIONS

In order to make a comparison it is necessary to distinguish between what characteristics will result in identification and what will not.  CLASS characteristics are not unique to a given object, while INDIVIDUAL characteristics are unique.  Whatever is being compared must possess class and/or individual characteristics.  Diagram #1 demonstrates class vs. individual characteristics, diagram #2 gives examples of class and/or individual while diagram #3 applies class and individual characteristics to latent prints.

Evidence possessing individual characteristics only:
In addition to friction ridge comparison, there exists only three types of forensic examinations that can result in conclusive matching: tool mark comparison, impression comparison (shoe prints, tire tracks, etc.), and the physical fit.  DNA blood typing is not individual as only a portion of the available DNA is being examined and even if DNA typing becomes individual, identical twins would have the same DNA blood type.  In each of these examinations (tool marks, shoe prints, physical fit & fingerprints), with sufficient individual characteristics, a trained examiner can determine if there is a unique connection between the questioned and reference material.  The possible results of the examination are shown in Diagram #4 and are “make (match),” “inconclusive,” or “elimination.”

Evidence possessing class characteristics only:
There is a multitude of evidence that only possesses class characteristics such as hair, fibers, gasoline, blood antigens, blood enzymes, paint metal, etc.  The only definitive conclusion that can be formulated is an “elimination.”  The strongest conclusion demonstrating a positive relationship is limited to “possibly” or “probably.”  And if no conclusion can be formed, the answer is  “inconclusive.”  See diagram #5.

Evidence possessing both class and individual characteristics:
Evidence from the first group discussed having individual characteristics may also have class characteristics.  When both are present there are four possible conclusions: “make,” “possibly,” “inconclusive” and “elimination.”  See diagram # 6.

LATENT PRINT EXPERT TESTIMONY

Latent print evidence:
A vast majority of latent print examiners use class characteristics to eliminate prints and use only individual characteristics when conducting a comparison.  The three categories that can be used when individual characteristics only are being compared are “make,” “inconclusive” and “elimination.”  The term “no make” (at our facility) includes both “inconclusive” and “elimination” and is used when the examiner did not conduct an “elimination” examination.  See diagram # 7.

Probably is an acceptable opinion in several forensic disciplines.  However, in friction ridge comparisons, the offering of an opinion of “probably or possibly” is not acceptable without qualifying or fully explaining the opinion1.  This standard is thought to have been set forth to protect this most highly respected discipline.  Realizing the ease in which a probable or possible   conclusion could be misinterpreted as having more significance than the evidence supports demands the strict adherence to the offering of only acceptable latent print opinions (make, inconclusive or elimination).