Evidence Without Related Firearm

The intercomparison of a number of recovered evidence bullets when no firearm was recovered should be performed according to laboratory protocol. This can be performed to link several bullets to a single firearm or to link several crime scenes together.

A sample procedure follows:

1. Mark the recovered evidence bullets.
2. 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.
3. Place the best bullet on the right stage of the comparison microscope. Attach the nose of the bullet to the mount.
4. Adjust the lighting from the rear of the microscope to provide oblique illumination over the bearing surface of the bullet.
5. 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.
6. Place a second evidence bullet on the left stage. Attach the nose of the bullet to the mount.
7. Adjust the lighting from the rear of the microscope to provide oblique illumination over the bearing surface of the bullet.
8. 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.
     
     Note: Such a difference could be due to deformed, damaged, or mutilated evidence bullets. If significant damage is not present, laboratory protocol for elimination should be followed (many laboratories require a minimum difference of 0.005 for elimination).
   • If the widths of the observed impressions are not significantly different, the examination should proceed.
9. 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.
   Note the following:
   • These examinations should be made with the bullets in phase. This means that the edges of the land and groove impressions of both bullets align with each other and the relationship of the other land and groove impressions in the viewing area is the same.
   • If either of the bullets are damaged or mutilated, this may not be possible.
   • Agreement is sufficient when it exceeds the best level of agreement demonstrated between bullet striations known to have been produced by different barrels (the best known non-match).
10. 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 for an inconclusive result may include the following:
    • The bullets were fired from different firearms.
    • Damage occurred to the bullets that caused distortion, deformation, or elimination of microscopic detail.
    • The firearm was damaged between firing the two bullets.
    
    Before deciding upon an inconclusive result, the following potential remedies should be explored:
    • Remount both bullets on their respective bullet mounts and reexamine.
    • Use magnesium smoke to enhance detail (smoking).
11. The above process should be repeated with all evidence bullets.
    
    Note: 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.

Back Forward