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Module 11: Bullet Comparison and Determination (AFTE Range of Conclusions,…
Module 11: Bullet Comparison and Determination
Firearms Identification
firearms-related specialized subset of toolmark identification
tool is defined as the harder of two objects
when the hard object is brought into contact with the softer object, the softer object will be marked
this is what happens when a fired bullet engages the rifling
striations
contour variations on the surface of an object caused by the combination of force and motion
Physical Characteristics
class characteristics
measurable features of a specimen that indicate a restricted group source
individual characteristics
marks produced by the random imperfections or irregularities of tool surfaces
subclass characteristics
discernable surface features of an object that are more restrictive than class characteristics
produced incidental to manufacture
significant because they relate to a smaller group source, that is, a subset of the class to which they belong
identifiable within a time frame since manufacturing processes change over time
Pattern Idenfication
the process of determining whether or not the striated toolmarks on two objects, such as fired bullets, correspond
the standard method for firearms identification
AFTE Range of Conclusions
identification
"agreement of a combination of individual characteristics and all discernable class characteristics where the extent of agreement exceeds that which can occur in the comparison of toolmarks made by different tools and is consistent with the agreement demonstrated by toolmarks known to have been produced by the same tool."
inconclusive
some agreement of individual characteristics and all discernable class characteristics, but insufficient for identification
agreement of all discernable class characteristics without agreement or disagreement of individual characteristics due to an absence, insufficiency, or lack of reproducibility
agreement of all discernable class characteristics and disagreement of individual characteristics, but insufficient for an elimination
elimination
significant disagreement of discernable class characteristics and/or individual characteristics
normally based on observed differences in any one of the general rifling characteristics
unsuitable for comparison
appropriate for fired bullet fragments that do not bear microscopic marks of value for comparison purposed
Bullet Examination
based on the following principles
the rifling in the barrel of a firearm bears unique microscopic characteristics due to manufacturing processes, use, and abuse
these characteristics mark the bearing surfaces of bullets when fired through the barrel
these individual characteristics are reproducible and identifiable with a particular firearm
comparison microscopy
used to establish identification and involves one of the following situations
recovered firearm without related evidence
obtain test bullets for later comparison by test firing the recovered firearm
recovered firearm with related evidence
obtain test bullets from evidence firearm and compare to recovered bullet to determine if the recovered firearm fired the evidence bullet
recovered bullets without related firearm
perform intercomparison to determine if recovered bullets are related to a single firearm