Interpretation Challenges

Rough handling and adverse environmental conditions can minimize the quantity of residues present. If this occurs, the results of muzzle-to-target determinations will be valid; however, the degree of specificity may be reduced.

It should be noted that the Modified Griess Test and the Sodium Rhodizonate Test yield positive reactions to nitrite compounds and lead respectively, whether or not the source is in fact from a gunshot. This dictates that the examiner make an informed interpretation. The location, distribution, and proximity to physical effects of residues present lend significance to the interpretation.

Read more about reporting interpretations in Module 14.

Examples of environmental and circumstantial conditions affecting interpretation include the following:

• Rough handling of victims clothing by emergency personnel may result in some loss of density in patterns of nitrite residues. Such a loss will not usually affect overall pattern size, thus permitting a distance determination based on the pattern.
• Wet weather conditions may degrade the amount of water soluble nitrite residues present. This can result in a loss so significant that only a maximum distance determination can be made.
• Large amounts of dried blood on clothing may mask both lead and nitrite residues.
• Extended exposure to high temperature and humidity may degrade nitrite residues. If pattern size can be developed, a distance determination can be made.
• Extended exposure of a body to the outdoors may eliminate the presence of nitrite residues. There is a high probability of finding lead residues, as they are not readily soluble in water.
• Large amounts of unburned ball powder fired from large-caliber handguns may be loosely and widely deposited on clothing. Transfer of residue across the garment may occur during the packaging and transportation of evidence, significantly reducing the value of chemical testing for nitrite residues.

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