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Module 12: Gunshot Residue and Distance Firearm Examiner Training Program…

- - - - Chemistry
        
        Acetic acid and heat are used to form nitrous acid, sulfanilic acid is added to form a diazonium compound, which is coupled with alpha-naphthol to produce a bright orange water-soluble azo nitrogen bearing dye. The reaction is preserved on a special coated paper for later comparison with GSR pattern of known distances.
      - Reagents and Test Media
        
        For examinations using this application.. a nitrite sensitive emulsion-coated test paper, nitrite swabs, glacial acetic acid in DI water, and a nitrite free cheesecloth are required.
      - Test Procedure
        
        Before "lifting" the GSR pattern, the nitrite sensitivity of the test paper should be confirmed. Then the evidence can be laid on top and reference points on the test paper can be marked. Then the solutions, cheese cloth and heat is used to cause the color producing reaction. The pattern on the paper can be examined and interpreted.
      - Color producing test detects nitrite compounds.
    - - The Modified Greiss Test can not be performed with nonpourous or thick surfaces. The Reverse Modified Griess Test uses the same materials but the heat is instead applied to the back of the test paper and not through the layers.
    - - Chemistry
        
        The material around a bullet hole is exposed to an ammonia solution then a dithiooxamide dissolved in ethanol solution. Copper bearing material will turn dark gray-green. Nickel bearing surfaces will turn blue-pink.
      - Reagents and Test Media
        
        For examinations using this application.. dithiooxamide, ethanol, ammonium hydroxide, DI water, white filter paper, source of copper, cotton swabs, and an eye dropper bottle are required.
      - Test Procedure
        
        Do all necessary preliminary examinations before hand (such as Modified Griess Test). Place copper test mark away from suspected copper areas( bullet holes). Place ammonium hydroxide moistened filter paper on area, press, turn over, drop dithiooxamide solution on filter paper, observe reaction, interpret results,
      - Detects copper
    - - Chemistry
        
        Spraying a saturated solution of sodium rhodizonate and DI water along with a solution of sodium bitartae, tartaric acid, and DI water will cause a pink reaction on lead and heavy metal bearing surfaces. A hydrochloric acid solution is then used to confirm the presence of lead with a color change to blue-violet.
      - Reagents and Test Media
        
        For examinations using this application.. a sodium rhodizonate in DI water solution, hydrochloric acid solution, and a buffer solution are required along with a known source of lead.
      - Test Procedure
        
        Do all necessary preliminary examinations before hand. Place a test mark on the surface, spray the suspected area and test mark area with all three solutions, observe results (blue-violet color reaction detecting lead), photograph, interpret.
      - Detects lead
    - - This test allows the detection of lead on dark clothing using similar chemistry as the Sodium Rhodizonate Test. A filter paper is used instead, placing it on top of the test area, spraying with acetic acid,and applying heat before removing the paper. Then the three solutions used in the Sodium Rhodizonate test are sprayed onto the filter paper to observe the reaction.