8127/frame/fm

2.
Three Inferences
Assuming the evidence is of sufficient quality,* three inferences are possible:
1. The items originate from difference sources.
2. The items may be classified but cannot be individualized due to a
limitation of the evidence or the test.
3. The items share a unique common origin.
a.
The Items Originate from Different Sources
We have already explained that differences will always exist between an evi-
dence and a reference item, even if they share a common source. When
differences are found, the examiner must determine if they are explainable
Inference:
to conclude from something known or assumed.
Opinion:
a judgment not based on absolute certainty or positive
knowledge, but on what seems true, valid, or probable to
one’s own mind.
Conclusion:
the last … division of a discourse, usually containing a
summing up of the points and a statement of opinion or
decisions reached
* It is assumed that both items have traits of sufficient quality and quantity for a legitimate
comparison. Otherwise no result or an inconclusive result might be obtained.
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Classification, Identification, and Individualization
139
or unexplainable. When a single 
unexplainable
difference is found, then the
analyst must conclude that the two items originate from different sources.
b.
The Items May Be Classified, but Cannot Be Individualized 
Due to a Limitation of the Evidence or the Test
Classification results when ambiguity is present in potentially individualiz-
able evidence. Ambiguity regarding the source of the evidence derives from
at least two circumstances. If the characteristics used for comparison are clear,
but are either too few in number or too common to convince the analyst
that the source is unique, then the inference falls short of individualization
and we are left with a 
classification
; the items may have originated from more
than one source. If potentially individualizing characteristics are present on
one of the items (usually the reference), but details are obscured on the other
(usually the evidence), it also may not be possible to infer a single common
source.
The latter situation is a direct consequence of the origin of forensic
evidence. Fingerprints are smudged, DNA is degraded, and bullets fragment
into tiny pieces. When such evidence is compared with a pristine reference
sample, only a portion of the pattern may be available for comparison. That
portion that is discernible may be indistinguishable from the reference, and
no data suggest that the reference is not the source of the evidence. However,
the comparison is based on partial information, and does not reach the level
of specificity required by the analyst to infer a single source. In this case, the
reference cannot be excluded as a possible source of the evidence, but the
analyst believes that other sources could also show these limited character-
istics, thereby allowing for multiple common sources. Additionally, clearer
traits in the evidence might reveal differences sufficient to eliminate the
possibility of a source in common with this reference.