Elimination Science

[C. Coppock]

Elimination is a scientific conclusion regarding a comparison that has satisfactorily passed a formal comparison methodology. Elimination must always be proven on a practical basis.

With elimination, the goal is to show that the friction skin of a particular person did not (could not) make that print impression. The difficulty is that, elimination does not necessarily represent a specific area of friction skin, but in most cases, all of the friction skin of a specific person. A conclusion of elimination states that; the subject was not the source of the friction skin print in question. An error of elimination can happen when the print impression, made by the subject, was overlooked by the examination team and/or there was an error in understanding the supporting statistics /uncertainties involved. It’s this second point that is the is misunderstood. The examiner may not understand that their conclusion of elimination is not scientifically supportable. Essentially, the scientific method was not followed in its proper format or in its intent.

With many comparisons, proving elimination can be extremely difficult. Yet, it must be provable according to the established guidelines for uniqueness and of sufficiency of information. Thus, it follows, that the certainty of elimination may remain unsubstantiated. As with a conclusion of individualization, elimination is also a formal scientific conclusion. Such a conclusion would need to be illustrated via prediction and comparison protocols coupled with thorough evaluation. In many cases, distorted and incomplete exemplars or comparison prints themselves do not allow for thorough comparison of predicted characteristics. Thus, these uncertainties would scientifically prevent a convincing conclusion of elimination. With regards to proof of elimination, the key word is practical, whereas the term practical applies to the limitations of a science-based application. “…There will never be a formal method of determining for every mathematical proposition (in our case prediction and comparison) whether it is absolutely true, anymore than there is a way to determine whether a theory in physics is absolutely true.” [1]

Assuming the examiner is qualified, we must understand the dynamics of the search difficulties to understand how accurate examiners can be. Remember the familiar adage of “A needle in the haystack?” This has a meaning that a search would prove very difficult, likely unsuccessful, or impossible. This is the equivalent to searching a low quality print impression, against a large and technically incomplete exemplar set or exemplar haystack. Technically, for a scientific exclusion of the needle from the haystack, one must show that each piece of hay does not conceal the needle or that the needle is too big to be concealed by the areas searched. With fingerprints, one may be able to show that the search print has a whorl pattern and the exemplars can be shown to contain no whorl patterns. Exclusion can then be proven, as it would not be possible for the print to have been made by the exemplar prints. If our search print lacks a pattern type or other level one feature, the difficulty of the search increases and the reliability of conclusions resulting from the search diminishes. This creates an increased level of uncertainty that can for a practical application, render a conclusion of elimination non-provable. A non-provable conclusion would also be an error of elimination. The correct hypothesis would be that the comparison is inconclusive. An additional aspect of uncertainty regarding exclusions is that the examiner’s mental search efficiency is reduced with lower quality print impressions.

The key to maintaining a reliable science is to understand what conditions of a comparison scientifically support exclusion. Examiners cannot presuppose that their assumptions would scientifically support exclusion. They need to understand that increased uncertainties regarding relevant information culminate in a need to consider an assessment of inconclusive. To routinely venture into a gray area such as attempting to prove exclusions with low quality information may not be the best approach. To maximize accuracy regarding exclusions, it may be appropriate to offer conclusions of exclusion only on a special case-by-case basis. One solution would be to state in some fashion that no identification was found, and when necessary state that the comparison is inconclusive regarding the fact that exclusion could not be proven. It is imperative to avoid non-supportable conclusions of fact. The main point here is to offer information that qualified experts have searched and did not find a match, and that exclusion is not provable with the information currently available.

In most criminal cases, the fact of exclusion offers little informational value regarding an investigation. Examiners understand that all surfaces touched by friction skin do not necessarily offer latent print impressions of identifiable quality. Therefore, the information regarding a conclusion of elimination may not actually offer information that could further an investigation. In fact in some cases investigators and jurors may be self mislead by assuming that a person did not touch an item. Fingerprint information by itself does not provide proof of guilt or of innocence. While properly formulated hypotheses of inconclusive are impartial, false information can be unintentionally injurious.

The collection and application of accurate information helps further an investigation while inaccurate information detours investigations. Examiners must remain cognizant of their science’s strengths as well as its limitations. This includes the limitations of the both the application and the examiner.

C. Coppock

1. Livio, Mario: 2003, The Golden Ratio (1.61803…), Broadway Books, NY p.240

[RL Tavernaro]

If I understand correctly (aside from the technical aspects), some salient points might be stated as:

• 1. Elimination/Exclusion, as applied to latent print comparisons, must be applied only on an individual print basis. Scientific standards and methodology must be applied, similar to requirements for an identification/individualization.
  
  2. Elimination/Exclusion may not be possible on every latent print (even if identifiable), given the available exemplars and qualitative/quanitative factors.
  
  3. An individual may be eliminated/excluded only as the source of an individual latent print. That elimination/exclusion must not be construed as applying to the entire item/surface, or other aspects of the case.

Essentially, a latent print identification enables the examiner to state that an individual has touched a particular item/surface. That information may in some cases be extrapolated to placing the individual at the scene of a crime.

The absence of a latent print identification does not, and cannot, eliminate/exclude an individual from having touched an item/surface, much less from being at the scene of a crime.

[clpexco]

Craig,

Great post... excellent food for thought.

I agree that we have to be careful to obtain a sufficient quality and quantity of detail for exclusion. As examiners, we should learn what that threshold entails, and apply standards to that conclusion based on our abilities, proficiency, training, experience, etc. etc.

I feel we also have to be careful that we don't confuse standards for conclusions with laziness. In the following passages, this concept could be emphasized more than it is:

If our search print lacks a pattern type or other level one feature, the difficulty of the search increases and the reliability of conclusions resulting from the search diminishes.

Just because no focal point exists in the latent print doesn't necessarily mean that the reliability of an exclusion decision diminishes... it just means, as you stated, that the difficulty of (or time involved in) the examination increases.

This creates an increased level of uncertainty that can for a practical application, render a conclusion of elimination non-provable.

Again, I would say this applies only to incomplete or non-clear exemplars where there is insufficient quality and quantity of detail to permit exclusion. The only uncertainty in a comparison with good quality exemplars and a poor quality but "sufficient" latent would come from an incomplete comparison, which may or may not be acceptable given the circumstances of the case. Let me explain a bit further:

If the known exemplars DO contain sufficient quality and quantity of detail to permit an exclusion to a small, and let's say low clarity impression with no focal points, then the examiner (or a superior) has to make an administrative type of decision as to what value the exclusion would have in that case. Such an examination might involve an extended period of time to conduct, and it takes on the form of a non-scientific decision to cease processing simply due to a trade-off between level of effort and return on investment. Would the administration rather have 5 examiners looking at 5 new cases, or making 5 difficult exclusions for one 8 hour day? It comes down to an issue of business and economics.

As you mentioned, if the known standards do not contain sufficient quality of detail in relevant areas of comparison, then in my opinion there is no basis, as you state, for an exclusion; simply an inconclusive or "no-identification" result, citing "additional exemplars" necessary for a complete examination.

There was one other sentence that struck me as concerning:

A non-provable conclusion would also be an error of elimination. The correct hypothesis would be that the comparison is inconclusive.

I would agree with this, but I wanted to emphasize that in your scenario there wasn't sufficient quality and quantity of detail in the known exemplar to be able to make an exclusion. Let me also expand this concept with an example: if a latent print contained a small area of ridges and detail flowing from one side to the other, but the palm prints did not contain a rolled hypothenar, then there is no valid basis on which to claim an exclusion. The latent could have come from the hypothenar, so the conclusion would need to be "inconclusive", (no identification), need additional exemplars for a complete comparison. What I think you are saying above is that IF the examiner stated "exclusion", then that conclusion would be in error. Fundamentally, I agree with you. Even though the examiner may have been "right" (additional exemplars "proove" him/her right), they were still "in error" in reporting "exclusion" when in fact it was not proovable at the time of the first comparison. In essence, the examiner would have reported "exclusion" erroneously... even though they were right.

Man, I love this job!! (and this forum!)

-Kasey

[C. Coppock]

Yep. There are considerable nuances to this topic of elimination. Ultimately, accuracy is the goal.