8127/frame/fm

 
5.
Interpretation and Conclusions
A criminalist must provide an interpretation of the evidence and a conclusion
about it. Not only is this role appropriate, it is obligatory. Above all, we must
remember that our aim is to present the scientific truth. The rendering of
an interpretation and the formation of a conclusion in a written report is
our last best chance to provide an understanding of the data outside of an
adversarial forum.
It is at this juncture that principles of criminalistics and the practice of
criminalistics intersect to become one and the same. The hypotheses have
been articulated, the evidence has been chosen, the laboratory work per-
formed, and the results recorded. What does it all mean? This brings us full
circle to a discussion of the very same issues we explored in detail in
Chapters 6 and 7. We will review some of these concepts briefly.
 
a.
Defining Facts and Assumptions
Earlier, we introduced you to the idea that an inference is based on both
assumptions and facts. This can be conveniently summarized as:
Some inferences rely on virtually no assumptions or very well grounded
assumptions; some may depend on less solid assumptions. Because changing
the assumptions might lead to a different inference, hence conclusion, the
underlying assumptions must be explicitly stated. Facts are rarely in dispute;
it is the assumptions about which experts argue, whether or not they realize
it. This model can be applied at any level of interpretation. It works as well
for an inference of association between two or more items as it does for an
inference of source.
If competing hypotheses are proffered, the assumptions leading to each
should also be clearly defined. For example, a common assumption made in
interpreting DNA profiles involves the number of donors who could have con-
tributed the evidence. Analysts rarely disagree about whether two profiles exhibit
matching patterns, it is the interpretation of complex patterns, especially profiles