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

- - - - Primer residues from the combustion of the cartridge priming mixture when the primer was struck by the firing pin
      - Residues resulting from the burning of the propellant
      - Material generated by the interaction of the bullet with the inside of the barrel
      - Unburned and partially burned powder
    - - Examination Documentation
        
        a. Visual, microscopic, and chemical examinations should be documented according to laboratory protocol.
      - Visual and Microscopic Examination
        
        a. The physical characteristics that may be visible during the preliminary examination for use in testing and interpretation include these:
        
        i. Hole in material
        
        ii. Visible ring around the perimeter of a hole, sometimes referred to as bullet wipe
        
        iii. Ripped or torn material in a stellate (star-shaped) pattern, consistent with a contact shot. When this is visible, especially in combination with burned, singed, or melted material, a distance determination can be made even in the absence of an evidence firearm.
        
        iv. Apparently burned or singed material, such as around a suspected bullet hole
        
        v. Melted tips of artificial fibers
        
        vi. Apparent heavy vaporous lead residue, often referred to as smoke, visible around a suspected bullet hole
        
        vii. Burned, partially burned, or melted gunpowder adhered to the surface
        
        viii. Types of gunpowder particles present (e.g., flake, disc, ball, flattened ball, etc.)
        
        ix. Apparent particulate other than gunpowder (e.g., lead shavings, tiny solidified droplets, copper jacket fragments, etc.)
      - Chemical Testing
        
        a. Up to three tests may be performed, but if there is more than one test that is performed, the following sequence is carried out
        
        i. Modified Griess Test for nitrite compounds, a product of burning a nitrate, such as smokeless powder, or Reverse Modified Griess Test
        
        • Chemistry process
        
        – Nitrite residues are exposed to an acetic acid solution and heat to form nitrous acid.
        
        – The nitrous acid combines with sulfanilic acid in the test medium to form a diazonium compound of sulfanilic acid.
        
        • Reagents and Test Media
        
        – Nitrite sensitive emulsion-coated test paper
        
        ∆ Prepare a solution of 7.7 grains (0.5 grams) of sulfanilic acid in 100 mL of distilled or deionized water.
        
        ∆ Prepare a solution of 4.3 grains (0.28 grams) of alpha-naphthol in 100 mL of methanol.
        
        ∆ Combine equal volumes of the above solutions.
        
        ∆ Pour the combined solutions into a nonreactive photo processing tray. Briefly submerge and remove precut sheets of the test paper into the tray.
        
        ∆ Set the sheets aside to dry on an uncontaminated surface or hang to dry.
        
        ∆ Store any unused solution in a sealed container labeled according to laboratory protocol.
        
        ∆ Store dried test paper in a dry place.
        
        – Nitrite test swabs (nitrite compound positive control samples)
        
        ∆ Prepare a solution of 9.3 grains (0.6 grams) of sodium nitrite in 100 mL of distilled or deionized water.
        
        ∆ Soak cotton tipped swabs in the nitrite solution.
        
        ∆ Set the swabs aside to dry.
        
        ∆ Store swabs in a sealed container labeled according to laboratory protocol.
        
        – Solution of glacial acetic acid (15%) and distilled or deionized water
        
        ∆ Combine 150 mL of glacial acetic acid with 850 mL of distilled or deionized water.
        
        ∆ Store the solution in a sealed container labeled according to laboratory protocol.
        
        – Nitrite compound-free cheesecloth
        
        ∆ Cut nitrite-free cheesecloth to the size of the process test paper.
        
        • Test Procedure
        
        – Confirm nitrite sensitivity of test paper.
        
        ∆ Using a nitrite test swab saturated with 15% acetic acid solution, dab the corners of the test paper. Each corner should turn orange, confirming the sensitivity of the paper to nitrite compounds. A negative control should also be tested for each sheet of photographic paper to ensure that it is not contaminated.
        
        – Mark reference points of evidence on test paper.
        
        ∆ Place the evidence face down on the emulsion-coated side of the test paper. Using a pencil, index any seams, buttonholes, buttons, rips, pockets, suspected bullet holes, tears, cuts, etc., for reference. Do not use ink because it may transfer back onto the evidence item.
        
        – Create layers of reaction items.
        
        ∆ Soak an unused piece of cheesecloth in the acetic acid solution. Wring excess solution from the cheesecloth and spread it on top of the evidence (already placed on the photographic paper), completing the three-layer sandwich.
        
        – Heat reaction layers.
        
        ∆ Press the layers with a hot uncontaminated iron. Acetic acid steam is forced through the layers, causing the color-producing reaction.
        
        – Examine and interpret the results.
        
        ∆ Discard the cheesecloth and separate the evidence item from the test paper. Any orange indications on the paper are the result of a chromophoric reaction chemically specific for the presence of nitrite residues.
        
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        – Label and retain test paper.
        
        ∆ Mark the previous pencil marks placed on the test paper in ink when the paper is dry. Label with additional data as called for by laboratory protocol.
        
        • Reverse Modified Griess Test
        
        – Confirm nitrite sensitivity of test paper.
        
        ∆ Tape a piece of filter paper to the back of a piece of nitrite-sensitive test paper. Using a nitrite test swab saturated with 15% acetic acid solution, dab the corners of the test paper. Each corner should turn orange, confirming the sensitivity of the paper to nitrite compounds.
        
        – Mark reference points of evidence on test paper.
        
        ∆ Arrange the evidence item face up and the treated paper emulsion side face down on the questioned surface. Using a pencil, index any points of reference.
        
        – Apply acetic acid solution to test paper.
        
        ∆ Wipe the emulsion-coated side of the test paper with cheesecloth saturated with the acetic acid solution. Lightly apply the solution to the entire surface. (Heavy application may cause indistinct or hazy results.)
        
        – Create layers of reaction items.
        
        ∆ Place the test paper emulsion side down on the evidence item. Apply heat using an iron to the back of the treated paper. (The back of the paper is covered by filter paper to prevent the iron from sticking to the treated emulsion-coated paper.)
        
        – Examine and interpret results.
        
        ∆ Separate the treated paper from the evidence item. Any orange indications on the paper are the result of a chromophoric reaction chemically specific for the presence of nitrite residues.
        
        – Label and retain test paper.
        
        ∆ Mark the previous pencil marks placed on the test paper in ink when the paper is dry. Label with additional data according to laboratory protocol.
        
        ii. Dithiooxamide Test (rubeanic acid test) for cuprous (copper-bearing) materials
        
        • Used in these types of ammunition
        
        – Military and sporting jacketed bullets fabricated from gilding metal (a 90/10 copper/zinc alloy) or commercial bronze (a 95/5 copper/tin alloy).
        
        – Rimfire bullets coated or plated with copper or brass (a 70/30 copper/zinc alloy).
        
        – Revolver bullets with copper jackets.
        
        – Nickel-plated bullets, e.g. Silver-tip bullets.
        
        • Chemistry process
        
        – Material from the perimeter of a suspected bullet hole is exposed to an ammonia solution.
        
        – The same material is exposed to a solution of dithiooxamide dissolved in ethanol. If cuprous material is present, a copper complex with a characteristic color forms.
        
        ∆ A dark gray-green color indicates the presence of copper-bearing material in bullet wipe.
        
        ∆ A blue-pink color indicates the presence of nickel (e.g., silver-tipped bullets).
        
        • Reagents and Test Media
        
        – Reagents and test media required for the Dithiooxamide Test
        
        ∆ Dithiooxamide
        
        ∆ Ethanol
        
        ∆ Concentrated ammonium hydroxide
        
        ∆ White filter paper
        
        ∆ Known source of copper
        
        ∆ Cotton swabs
        
        ∆ Eye dropper bottle
        
        – Dithiooxamide Solution
        
        ∆ Prepare a 0.2% weight/volume solution of dithiooxamide in 100% ethanol.
        
        ∆ Store in a sealed container labeled according to laboratory protocol.
        
        – Ammonium Hydroxide Solution
        
        ∆ Prepare a 1:2 dilution of concentrated ammonium hydroxide using distilled or deionized water under a chemical hood.
        
        ∆ Store in a sealed container labeled according to laboratory protocol.
        
        • Test Procedure
        
        – Confirm performance of all preliminary examinations and tests.
        
        ∆ The Modified Griess Test must be performed before this test.
        
        – Place a test mark on the item to be tested.
        
        ∆ Using a piece of known copper, place the mark well away from any holes to be tested. (Note: Apply the following steps to the test mark first to ensure the reagents are reacting properly and then apply to the questioned area.)
        
        – Position the area to be tested.
        
        ∆ Place the test mark or suspected bullet hole face up on a clean uncontaminated surface.
        
        – Perform color test.
        
        ∆ Place three drops of ammonium hydroxide solution on one half of folded filter paper.
        
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        – Examine and interpret results.
        
        ∆ Dark gray-green color indicates the presence of copper-bearing material.
        
        ∆ Blue-pink color indicates the presence of nickel (e.g., silver-tipped bullets).
        
        – Dry test item.
        
        ∆ Allow tested item to dry out before additional testing.
        
        iii. Sodium Rhodizonate Test for all forms of lead residues or Bashinski Transfer Technique
        
        • Chemistry process
        
        – The questioned area is sprayed directly with a saturated solution of sodium rhodizonate in distilled or deionized water.
        
        – A buffer solution (pH 2.8) consisting of sodium bitartrate and tartaric acid in distilled or deionized water is then sprayed on the area.
        
        ∆ Any pink reaction which results may indicate lead or a number of other possible heavy metals. The presence of lead may be confirmed through an additional step.
        
        – A dilute solution of hydrochloric acid is applied by spraying the area.
        
        ∆ The color results are dependent on the degree of acidity and the presence of lead. If the pink area changes to a blue-violet color, the presence of lead is confirmed.
        
        • Reagents and Test Media
        
        – Reagents and test media required for the Sodium Rhodizonate Test
        
        ∆ Saturated solution of sodium rhodizonate dissolved in distilled or deionized water
        
        ∆ Buffer solution of 2.8 pH consisting of sodium bitartrate and tartaric acid in distilled or deionized water
        
        ∆ Solution of hydrochloric acid (5%) in distilled or deionized water
        
        ∆ A known source of lead
        
        – Sodium Rhodizonate Solution
        
        ∆ Add a sufficient amount of distilled or deionized water to a small amount of sodium rhodizonate in a small beaker to form a saturated solution that is approximately the color of dark tea.
        
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        – 2.8 pH Buffer Solution
        
        ∆ Dissolve 29.3 grains (1.9 grams) of sodium bitartrate and 23.1 grains (1.5 grams) of tartaric acid per 100 mL of distilled or deionized water. Heat on a hot plate while agitating with a magnetic stirrer to create the solution quickly.
        
        ∆ Store in a sealed container labeled according to laboratory protocol. The shelf life of the solution is limited.
        
        – Hydrochloric Acid Solution
        
        ∆ Combine 5 mL of concentrated hydrochloric acid with 95 mL of distilled or deionized water. Carefully pour the acid into the water to preclude the spattering of acid.
        
        ∆ Store in a sealed container labeled according to laboratory protocol.
        
        • Test Procedure
        
        – Confirm performance of all preliminary examinations and tests.
        
        ∆ The Modified Griess Test and the Dithiooxamide Test must be performed before this test.
        
        – Place a test mark on the item to be tested.
        
        ∆ Using a known piece of lead, place the mark well away from any areas to be tested.
        
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        – Position the area to be tested.
        
        ∆ Place the test mark or suspected bullet hole face up on a clean uncontaminated surface.
        
        – Perform color test.
        
        ∆ Spray the test area with the saturated solution of sodium rhodizonate.
        
        ∆ Spray the same area with the buffer solution.
        
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        ∆ Spray the same area with the hydrochloric acid solution.
        
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        • Bashinski Transfer
        
        – Position the area to be tested.
        
        ∆ Place a piece of laboratory filter paper over the test area.
        
        – Place a test mark on the filter paper.
        
        ∆ Index the filter paper in pencil relative to the test item indicating the location of suspected bullet holes, seams, buttons, button holes, pockets, rips, tears, etc., for future reference.
        
        – Prepare the filter paper.
        
        ∆ Dampen the filter paper uniformly while positioned on the test item by spraying with a 15% solution of glacial acetic acid in distilled or deionized water.
        
        – Lift residues from item.
        
        ∆ Cover the dampened filter paper with several layers of dry filter paper and apply heat with an iron until the paper is dry.
        
        – Perform color test.
        
        ∆ Remove the original filter paper from direct contact with the test item.
        
        ∆ Spray the filter paper with the saturated solution of sodium rhodizonate.
        
        ∆ Spray the filter paper with the buffer solution.
        
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        ∆ Spray the filter paper with the hydrochloric acid solution.
        
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        – Label and retain test paper.
        
        ∆ Mark the previous pencil marks placed on the test paper in ink when the paper is dry. Label with additional data according to laboratory protocol. This result can fade quickly; observations should be photographed and documented promptly.
  - - - Residues may be absent
        
        a. Careless evidence handling
        
        b. Life-saving efforts of emergency medical personnel
        
        c. An intervening object at the time of discharge
        
        d. Masking of gunshot residues by dried blood or other debris
        
        e. Shot fired from a distance beyond the maximum distance for the deposit of any residue
    - - Physical effects
        
        a. Ripping and tearing of cloth
        
        b. Burning and/or singeing of cloth
        
        c. Melted tips of artificial fibers
        
        d. Heavy vaporous lead (smoke) deposits around a suspected bullet hole
    - - Results are useful in
        
        a. Determining the maximum distance of the vaporous lead deposits
        
        b. Corroborating the results of the Modified Griess Test
    - - 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.
    - - Sources of testing ammunition
        
        a. evidence ammunition from the case, per laboratory protocol
        
        b. purchased ammunition (same brand, stock number, with the same powder, projectile and primer components)
        
        c. reference ammunition (same brand, stock number, with the same powder, projectile, and primer components)
    - - Buckshot pattern may have fewer holes present as a result of one or more
        
        a. Multiple pellets could pass through a single hole.
        
        b. An intermediate object may be involved at the time of discharge.
        
        c. Factory loaded shotshell may not contain the number of pellets indicated by the manufacturer.