Emedinews:Insights on Medicolegal Issues:How can the firearm discharge residue on hands of accused be collected by the doctor?

Nitrate and nitrite residue may be found on medical examination and can be recovered from the skin by occlusion in a layer of melted paraffin during medical examination. Another test for skin residue involving paraffin as the collecting medium is for metallic elements in trace amounts, which result from primer residue. The analyses are made with neutron activation by ballistic expert.

•        The test is known as the ‘dermal residue test’ or ‘paraffin glove test’. The important factor is to place the responsibility of interpretation of results in the hands of the forensic scientist, not the doctor

•        Atomic absorption and x–ray dispersive energy spectrometry methods are also useful in identifying and quantifying metallic residues from weapon firing.

•        Currently, a screening technique is used to check the hands, clothing and other objects where circumstances warrant the examination. The main element examined for is lead, which appears to originate chiefly from the primer composition

•        Swabs are taken from appropriate areas on small clean cotton cloth squares moistened with a few drops of 1% lead–free hydrochloric acid and air dried.

•        A few drops of reagent are applied to the swab area on the cloth which is again dried. If the lead is present it is indicated by the development of a characteristic purplish–blue color.

•        The interpretation of such results should be left to an experienced examiner as positive results do not necessarily prove the subject fired a gun nor a negative result wholly precludes the firing.