Firearms Discharge Residues on Hands

GEORGE PRICE

Ballistics Section, Home Ofice Forensic Science Laboratory, Nottingham, England

In a recent death by shooting investigation, in which this laboratory was involved, i t was desired to establish whether or not a revolver bullet head wound had been self inflicted. This necessitated a careful re-appraisal of the possible methods of detecting residues on the hands arising from the discharge of a firearm.

Previous work Previous experiments carried out by the author, mainly directed towards

the detection of nitrates and nitrites, had been regarded as inconclusive and unreliable. Investigations along these lines have also been carried out by other workers with similar results.

Recent work by Guinn (1964) has shown that traces of antimony and barium (present in many cartridge priming charges) are deposited on the web of the thumb and back of the hand as a result of firing a revolver. These traces can be detected and measured by the application of neutron activation analysis. Investigations employing similar methods are being undertaken a t the Atomic Weapons Research Establishment, Alderrnaston, on behalf of the Home Office. (The author is co-operating in this work).

I t was felt that, in addition to the above method of detecting discharge residues, it might be desirable to have a quick, on-the-spot test which would be of immediate value to the investigating officer. With this in mind, Harrison & Gilroy's work (1959) appeared to offer such a test, and has, in consequence, been given careful consideration. However, the results of such tests carried out so far have been disappointing and tend not to bear out fully the published findings.

Lead detection using sodium rhodizonate Experiments based on the detection of lead using the sodium rhodizonate

test reported by Feigl (1943) have been carried out. As a result of these experi- ments to date, i t has been established that it is possible, under certain conditions, to detect traces of lead on the hand of a person having fired a pistol.

When a lead bulletted cartridge is fired from a revolver the chances of detecting lead by this method are rated very high. In 100 test firings, 90 good positives, 8 negatives and 2 doubtful positives were recorded. When jacketted lead bullets are fired, although the amounts of lead deposited appear to be rather less, the detection rate is still of the same order. The amounts of detectable lead vary with the make and condition of the revolver, but little variation has been noted with different makes of ammunition.

Results of tests carried out in connection with the discharge of self-loading pistols indicate that lead deposits are less likely than is the case with revolvers, and these again vary considerably depending on the design of the pistol. Nevertheless, something of the order of 60% positive tests have been obtained. The figure is higher in the case of .22" calibre pistols which use unjacketted ammunition.

Increased amounts of lead are often detected on the hand when the discharge of the weapon is from a close range, indicating possible "blow back" of traces from the target. Where a number of successive shots are fired, tests indicate a build-up of lead deposits on the hand.

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Tests for the presence of lead on the ball of the thumb and fingers used for loading the cartridge into the firearm give strong positives in the case of un- jacketted lead bullets, and even when the ammunition is jacketted, the results are usually positive.

In the case of firearms where the breech remains closed after firing, such as shot guns and rifles, it has not been possible to detect traces of lead by this method. Clearly, positive tests for lead under these circumstances call for careful evaluation, bearing in mind possible occupational contamination of the hands. However, no false positives have so far been experienced. Normal washing of the hands appears to remove traces detectable by this method. I t is considered that this type of test may a t least form the basis of a good screening test, and for this reason alone it is worthy of careful consideration where the circumstances of a case indicate the need for this line of enquiry.

The sodium rhodizonate test is also useful in the detection of lead deposits adjacent to suspected bullet damage in clothing, etc.

Technique A number of methods for the removal of discharge residues from the hand

have been tried out. The method found to be most satisfactory consisted of the use of a swab made up from a piece of cotton cloth (approx. 1" square) with a pea-sized piece of absorbent cotton wool twisted into the centre to form a pad. The pad moistened with 1% hydrochloric acid is then used to swab the weband back of the thumb and forefinger. The cotton wool is removed and the cloth is warm-air dried. The centre of the cloth is then treated with a drop of sodium rhodizonate solution (freshly prepared). A red colour which turns blue on the addition of 5% hydrochloric acid indicates the presence of lead.

Reagents 1% aqueous HC1. v/v. Sodium rhodizonate saturated aqueous solution 5% aqueous HC1. v/v.

References GUINN, V. P., 1964, Methods of Forensic Science, 3, 64 HARRISON, H. C., & GILROY, R., 1959, Journal of Forensic Sciences, 4, 184 FEIGL, F., 1943, Laboratory Manual of Spot Tests, pp. 130-135, Academic Press,

New York.