Time of Firing of Revolvers in Suicide Cases
J K Sinha & C N Bhattacharyya
[Presented at All India Forensic Science Conference (India)1985]
ABSTRACT
An estimate of time lapse, since a firearm was fired last, provides useful corroborative evidence in reconstructing the scene of occurrence. The phenomenon of escape of discharge gases from fired shot shells has been utilised by Sinha *to estimate approximate time of firing. This phenomenon could not be utilised for firearms because the rate of escape of discharge gases is expected to vary significantly with the number of fires and with the upkeep of firearm , before and after the commission of crime till its recovery. These variable factors are minimised if the firearm is used for committing suicide.
The incident of firing, for committing suicide, very often, attracts the notice of victim's relative and neighbours. The firing incident is brought to the notice of the enforcement agencies within a very short time, usually within few hours or so. The involved firearm is ,therefore, expected to be recovered in undisturbed condition. If it is a revolver, the fired cartridge case will also be recovered in the chamber at 12 o'clock position. The number of fired rounds in a suicide is also expected to be the only one. Revolver is usually the personal firearm of the victim, licensed or otherwise. As such, it is ordinarily kept in cleaned condition. Therefore, under normal circumstances, one would expect recovery of the revolver in undisturbed condition with the fired case in the 12 o'clock chamber, allowing the free escape of discharge gases only after one single fire from a cleaned barrel. The variation in weather condition (temperature, pressure, humidity, etc), is likely to be insignificant during the short interval between the firing incident and the recovery of the firearm.
Possibility of estimation of time of firing of revolvers in suicide cases, by utilising the phenomenon of escape of discharge gases, has been investigated in the present paper. Five .32 revolvers were chosen for the study. The escaping gases from the muzzle were subjected to chemical tests for detection of nitrite ion by diazotisation and coupling reaction. The intervals chosen were 6 hours after firing and after every 24 hours up to 10 days. Each revolver was placed on a suitable stand muzzle pointing upwards. A thin plastic piece having a small hole at the center, was kept on the muzzle.Small filter paper piece, slightly more than the hole size, was kept on the plastic piece. Two drops of freshly prepared reagent* (L-napthylamine and sulfanilic acid in acetic acid) were placed on the filter paper. The escaping gases developed pink colour on the filter paper. The time taken to develop colour in relation to the time lapse for each interval was noted. Though no linear relationship could be established for all possible time intervals, the observations revealed that irrespective of the type of the revolver used ,whether regular or improvised, the time taken to develop colour after a lapse of 6 hours of firing was well within a minute. The interpretation of experimental results provided valuable clue for elimination or corroboration of firing within a short interval of few hours or so. The suggested method can be adopted at the investigation stage, if the suicide incident is brought to the notice of the enforcement agencies within few hours. Different criteria for elimination and corroboration has been suggested. The experimental results and discussion have been detailed in the present paper. The procedure to be adopted in actual cases and the caution required in evaluating the observations have been discussed.**
** Accepted for publication.
* Time of firing of shot shells. J. Forensic Science, USA. 21(1976)171-175.
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