When evidence of the identity of some particular arm can be established both by the evidence of a fired bullet and that of a fired cartridge case, the question may arise as to which is the more reliable. There can only be one answer: both are equally reliable provided both can be put forward in a manner which can be appreciated and understood by a non-technical jury. This is the crux of the whole matter, for it is far more difficult to establish identity by means of a fired bullet than by means of a fired cartridge case. Apart from the obvious possibility of the bullet being so deformed as to render all examination abortive, there is far more chance of a good thumb-mark of any weapon being imprinted on the base of a fired cartridge case by static pressure, than it has of being engraved on a bullet by a sliding pressure. And the thumb-mark on the cartridge is not only far more easy to read, but it is far more easy to photograph than is that on a bullet.
Further, photographs of the bases of cartridge cases are more readily appreciated and understood by a nontechnical jury than those of the striations on fired bullets.
In the Gutteridge case the late Colonel H. W. Tod-hunter, C.M.G., the then Chief Inspector of Small Arms, and his staff, who did all the work of identification, effected this identification both by means of a fired cartridge case and by two fired bullets. These bullets were fired from different revolvers and were actually matched to the two revolvers found in the possession of the accused men, thus proving that both weapons were used for the murder. Yet the prosecution only brought forward the cartridge evidence, as this was all that was needed to prove their case, and the bullet evidence was considered too complicated to explain satisfactorily to a jury. But this bullet evidence was all ready and available in case of need, and the defence were informed of this fact.
There is also the chance that a sufficient number of rounds may have been fired between the firing of the "crime" bullet and the finding of the suspect pistol to render the task of identification by means of the bullet impossible. But the breech face of a weapon is unaffected by wear, although it may in time become pitted by corrosion. But such a process is slow and will probably take years, and even then some of the major markings may remain sufficiendy distinct to enable identity to be established.
Naturally the idea must present itself of the possibility of a criminal altering the thumb-mark of his weapon. It would be a comparatively easy matter to alter the thumb-mark of a barrel, and this fact must always constitute a possible weakness in the work of identification by means of bullets. At the same time if the barrel were scoured out crudely, as it probably would be, the results should be quite obvious to any competent firearms expert, and the very fact that the barrel had been so treated would cast grave suspicion on the owner of the weapon.
But a breech face is far more difficult to alter. In fact, in the case of many makes of self-loading pistols it would require a competent worker to strip the mechanism so as to be able to get at the breech face with a tool. The breech face of a revolver would easily be filed. But such filing would again be obvious and merely throw suspicion on the owner of the revolver.
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