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Firearms Examiner Training. Dillon JH, Jr. 2013. Firearms Examiner…

- - - - Three categories
        
        a. Class characteristics
        
        i. Measurable features of a specimen that indicate a restricted group source. They result from design factors and are therefore determined before manufacture. In the context of this module, general rifling characteristics of the barrel of a firearm are the class characteristics of interest.
        
        b. Individual characteristics
        
        i. Marks produced by the random imperfections or irregularities of tool surfaces. These random imperfections or irregularities are produced incidental to manufacture and/or are caused by use, corrosion, or damage. They are unique to a particular tool and distinguish it from all other tools. In the context of this module, the tool is the interior of the barrel of a rifled firearm.
        
        c. Subclass characteristics
        
        i. Discernable surface features of an object that are more restrictive than class characteristics in that they are:
        
        • 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
  - - - Important in consideration of
        
        a. The expectations of more sophisticated jurors
        
        b. The need for more objective identification criteria
        
        c. The changing environment of the courtroom following Daubert v. Merrell Dow Pharmaceuticals
        
        d. The potential for increased credibility for examiners in the courtroom
  - - - The theory of identification as it pertains to the comparison of toolmarks enables opinions of common origin to be made when the unique surface contours of two toolmarks are agreement.
      - This sufficient agreement is related to the significant duplication of random toolmarks as evidenced by the correspondence of a pattern or combination of patterns of surface contours. Significance is determined by the comparative examination of two or more sets of surface contour patterns comprised of individual peaks, ridges, and furrows. Specifically, the relative height or depth, width, curvature and spatial relationship of the individual peaks, ridges, and furrows within one set of surface contours are defined and compared to the corresponding features in the second set of surface contours. The agreement is significant when it exceeds the best agreement demonstrated between toolmarks known to have been produced by different tools and is consistent with agreement demonstrated by toolmarks known to have been produced by the same tool. The statement that sufficient agreement exists between two toolmarks means that the agreement is of a quantity and quality that the likelihood another tool could have made the mark is so remote as to be considered a practical impossibility.
        
        a. Sufficient Agreement and Best Known Non-Match
        
        i. Ultimately, sufficient agreement is the product of the individual examiners training, skills, and experience in
        
        • Recognizing corresponding patterns of matching striations
        
        • Recognizing corresponding patterns within impressed toolmarks
        
        • Determining the best known non-match in their personal experience
        
        • Comparing striated and impressed toolmarks
      - Currently, the interpretation of individualization/identification is subjective, founded on scientific principles and based on the examiner's training and experience.
  - - - 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.
    - - Fired bullet fragments
      - Jacket fragments
      - Lead bullet cores
      - Lead fragments
      - Other portions of fragmented, mutilated, or otherwise damaged bullets
      - Metallic fragments that cannot be identified as having been a part of a fired bullet (often the product of crime scene searches where all small metal items were collected).
  - - - 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.
    - - Recovered firearm without related evidence
        
        a. Obtain test bullets for later comparison by test firing the recovered firearm.
        
        i. Reasons
        
        • To determine if the firearm reliably reproduces microscopic marks on test fired bullets that are suitable for comparison purposes.
        
        • To allow the examiner to assess the quality of marks produced by the firearm.
        
        • To retain physical samples of bullets fired from all firearms entering the laboratory.
        
        – Comparison with new evidence submissions at a later time.
        
        ∆ Comparison Process
        
        2 more items...
        
        – Entry into digital image reference files.
      - Recovered firearm with related evidence
        
        a. Obtain test bullets from evidence firearm and compare to the recovered bullet to determine if the recovered firearm fired the evidence bullet.
        
        i. A sample procedure
        
        • Mark the recovered evidence bullet.
        
        • Use a stereomicroscope to determine that the recovered evidence bullet has microscopic marks of value and is suitable for comparison.
        
        • Use the comparison process described previously to confirm that the test bullets from the recovered firearm can be identified with each other.
        
        • Place the best test bullet on the right stage of the comparison microscope. Attach the nose of the bullet to the mount.
        
        • Place the recovered evidence bullet on the left stage of the comparison microscope. Attach the nose of the bullet to the mount.
        
        • Adjust the lighting equally from the rear of the microscope to provide oblique illumination over the bearing surface of both bullets.
        
        • Rotate the test bullet, placing the previously marked index area in the center of the viewing area.
        
        • Align a land impression (or a groove impression) on the recovered evidence bullet with the indexed area on the test bullet. Confirm whether or not the widths of the observed impression are the same for both bullets.
        
        – Elimination
        
        ∆ If the widths of the observed impressions are significantly different, it may be possible to conclude that the recovered evidence bullet was not fired from the recovered firearm. This concludes the examination of this recovered evidence bullet.
        
        1 more item...
        
        ∆ If the widths of the observed impressions are not significantly different, the examination should proceed.
        
        • Rotate the recovered evidence bullet to search for individual characteristics similar to those found on the previously indexed area of the test bullet. If these are found, compare all undamaged bearing surfaces of the recovered evidence bullet with the corresponding areas on the test bullet.
        
        – Identification
        
        ∆ If the recovered evidence bullet is damaged or deformed in the area previously indexed on the test bullet, it may be necessary to use other areas of the test bullet to compare to the undamaged areas of the recovered evidence bullet.
        
        ∆ If there is sufficient agreement for identification, the recovered evidence bullet should be indexed in the same area as the test bullet, even if this is a damaged area.
        
        ∆ If the recovered evidence bullet is missing the area indexed on the test bullet, the best area for comparison on the recovered evidence bullet should be indexed with a different color. The test bullet must be indexed again in the area of agreement and with the same color as used on the recovered evidence bullet.
        
        ∆ Document the area of agreement according to laboratory protocol.
        
        • Proceed with additional examinations if the recovered evidence bullet cannot be indexed, identified, or eliminated as having been fired from the recovered firearm. These additional examinations are performed to determine the conditions or circumstances that may have caused the inconclusive result.
        
        – Inconclusive
        
        ∆ Reasons
        
        7 more items...
        
        ∆ Remedies
        
        3 more items...
      - Recovered bullets without related firearm
        
        a. Perform inter-comparison to determine if recovered bullets are related to a single firearm.
        
        i. A sample procedure
        
        • Mark the recovered evidence bullets.
        
        • Use a stereomicroscope to determine that the recovered evidence bullets have microscopic marks of value and are suitable for comparison. Group the bullets according to levels of damage and/or the amount of individual characteristics.
        
        • Place the best bullet on the right stage of the comparison microscope. Attach the nose of the bullet to the mount.
        
        • Adjust the lighting from the rear of the microscope to provide oblique illumination over the bearing surface of the bullet.
        
        • Examine the entire bearing surface of the bullet using low magnification (10x-20x) to determine the best area of individual characteristics. When such an area is located, leave the right stage in that position.
        
        • Place a second evidence bullet on the left stage. Attach the nose of the bullet to the mount.
        
        • Adjust the lighting from the rear of the microscope to provide oblique illumination over the bearing surface of the bullet.
        
        • Align a land impression or groove impression of the two bullets to determine if the widths are the same.
        
        – Elimination
        
        ∆ If the widths of the observed impressions are significantly different, it may be possible to conclude that the recovered evidence bullets were not fired through the same barrel. This concludes the examination of these recovered evidence bullets.
        
        1 more item...
        
        ∆ If the widths of the observed impressions are not significantly different, the examination should proceed.
        
        • Rotate the bullet on the left stage to search for individual characteristics similar to those found on the bullet on the right stage. If these are found, compare all undamaged bearing surfaces of the recovered evidence bullet on the left stage with the corresponding areas of the evidence bullet on the right stage.
        
        – Identification
        
        ∆ If there is sufficient agreement for an identification, both recovered evidence bullets should be indexed.
        
        ∆ Document the area of agreement according to laboratory protocol.
        
        3 more items...
        
        • Proceed with additional examinations if the recovered evidence bullets cannot be indexed, identified, or eliminated. These additional examinations are performed to determine the conditions or circumstances that may have caused the inconclusive result.
        
        – Inconclusive
        
        ∆ Reasons
        
        3 more items...
        
        ∆ Remedies
        
        2 more items...
        
        • The above process should be repeated with all evidence bullets.
        
        – It may be necessary to use more than one evidence bullet to establish a chain of identifications within a set of submitted bullets. Recovered evidence bullets may be damaged, precluding examination of some land and groove impressions. Examination of different areas of these bullets may be necessary to link all the recovered evidence bullets.
    - - Preliminary steps
        
        a. Review laboratory protocols, as needed
        
        b. Complete administrative requirements
        
        i. Chain of custody
        
        ii. Marking of evidence
        
        iii. Laboratory case identifiers
        
        iv. Investigative file identifiers
        
        v. Examiner identity
        
        vi. Quality assurance
        
        c. Follow laboratory safety protocols
        
        d. Determine the presence of trace evidence and follow laboratory protocol for collection
        
        i. Examples of trace evidence include
        
        • Paint
        
        • Glass
        
        • Blood
        
        • Bone
        
        • Soft tissue
        
        • Hair
        
        • Fibers
        
        • Wood
        
        • Metal smears
        
        • Masonry
        
        • Stone
        
        e. Determine if latent fingerprint examinations should be performed prior to toolmark examinations
        
        f. Determine if other examinations (not requested) should be performed. If so, coordinate with the investigator.
    - - Bullet Surface Replication
        
        a. This situation can arise due to
        
        i. NIBIN-related high-probability associations (hits) made in a remote laboratory that must be physically examined using a comparison microscope,
        
        ii. routine liaison with examiners from other jurisdictions concerning possibly related cases,
        
        iii. information provided to investigators by an informant indicating possible case linkages between cases from different jurisdictions.
        
        b. Administrative obstacles that can prevent or delay the physical comparison
        
        i. chain of custody concerns (integrity of evidence) on the part of investigative agencies and prosecutors offices,
        
        ii. policies relating to the shipment or transport of evidence to other laboratories or jurisdictions,
        
        iii. budgetary constraints regarding long distance travel to other jurisdictions.
      - Procedure
        
        a. Mix the components of the casting material until the mixture begins to harden.
        
        b. Apply the mixture to the surface of the fired bullet and allowed to completely harden.
        
        c. Remove the cast when it has hardened.