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Fired Case Examination

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Fired Case Examination

Side by side comparison of breechface marks
Side by side comparison of breechface marks
Courtesy of Jack Dillon (see reuse policy).

As in the case of fired bullets, the microscopic comparison and potential identification of fired cartridge cases and shotshell cases as having been fired from the same firearm is at the core of forensic firearms work.

The comparison will involve one of the following situations:


Fired Case Examination Situations
Situation Action
Recovered firearm without related evidence Obtain pairs of test cartridge cases for later comparison by test-firing the recovered firearm.
Recovered firearm with related evidence Obtain test cartridge cases or shotshell cases from an evidence firearm and compare to evidence cartridge cases or shotshell cases recovered from a crime scene to determine if the evidence firearm fired the evidence cartridge case or shotshell case.
Recovered evidence without related firearm Compare evidence cartridge cases or shotshell cases recovered from multiple bodies or crime scenes to determine if the scenes are related to a single firearm.


Microscopic Procedure

The following preliminary steps should be addressed prior to any of the case comparisons:

  • Review laboratory protocols, as needed.
  • Complete administrative requirements:
    • Chain of custody.
    • Marking of evidence.
    • Laboratory case identifiers.
    • Investigative file identifier.
    • Examiner identity.
    • Quality assurance.
  • Follow laboratory safety protocols.
  • Determine the presence of trace evidence and follow laboratory protocol for collection.

    Examples of trace evidence:
    • Paint.
    • Glass.
    • Blood.
    • Bone.
    • Soft tissue.
    • Hair.
    • Fibers.
    • Wood.
    • Metal smears.
    • Masonry.
    • Stone.
  • Determine if latent fingerprint examinations should be performed prior to toolmark examinations.
  • Determine if other examinations (not requested) should be performed. If so, coordinate with the investigator.

Microscopic Comparison

  • Ensure that stereo and comparison microscopes meet all maintenance and calibration standards.
  • Select an appropriate level of magnification for both objective lenses of the comparison microscope. Typically, this setting will be 1x or 2x. Ensure that the objective lenses are locked in place.
  • Select the appropriate level of magnification for both ocular lenses. This would typically be 10x.
  • Select the same type and orientation of light source for each comparison microscope stage. Many examiners prefer strong fluorescent or fiber-optic lighting.


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