The following excerpt is taken from Criminal Investigation: A Practical Handbook for Magistrates, Police Officer, and Lawyers, by Austrian professor and magistrate, Hans Gross. The original 2-volume work was published in 1893; this is from a 1906 edition, “translated and adapted to Indian and Colonial practice” by John Adam J. Collier-Adam, both barristers in Madras, India, and available online at archive.org.* This section has no paragraph divisions; I have added some for better online readability.
“On the other hand, the presence of the weapon is for the most part quite indifferent; it is common to find no weapon beside persons who have undoubtedly committed suicide. This is generally attributed to the theft of the weapon by those arriving first on the scene, the weapon used by a suicide being usually supposed to produce superstitious effects. The following is a most instructive case.
Early one morning the authorities were informed that the corpse of a murdered man had been found. At the spot indicated, in the middle of a bridge crossing a rather deep stream, the body was found of a grain merchant, A.M., supposed to be a well-to-do man, face downwards with a gun shot wound behind the ear. The bullet after passing through the brain had lodged in the frontal bone above the left eye. His pocket-book was missing and the seam of the inside pocket in which it was usually carried was ripped up, as if the pocket-book had been rapidly and violently snatched out. His watch and chain were also missing, of the latter the ring attaching it to the waistcoat button was alone left. A policeman stated that A.M. had been seen the evening before in a spirit shop, were he drank with moderation and left about 10:30 pm, stating that he was about to return home. To reach his house he had to pass over the bridge where he was found dead. In the spirit shop there was at the same time as A.M., an unknown, wretched-looking man, who throughout the evening drank but a single glass of spirits and left shortly after A.M. The latter had several times taken out his pocket-book, which appeared well-filled, though no one could say whether he had any money or how much. The supposition was therefore natural that the unknown had followed A.M., murdered him on the bridge, and robbed him; he was accordingly searched for, arrested, and brought to the spot. He denied all knowledge of the crime and said he passed the night in a barn, which however he could not point out to the police.
Just when the inquiry was concluding and the corpse was about to be removed after the post-mortem, the Investigating Officer observed quite by chance that on the decayed wooden parapet of the bridge, almost opposite the spot where the corpse lay, there was a small but perfectly fresh injury which appeared to have been caused by the violent blow on the upper edge of the parapet of a hard and angular body. He immediately suspected that this injury had some connection with the murder; examination with a magnifying glass showed nothing important, but it was impossible to avoid the impression that here the murderer had thrown something into the water and thus damaged the parapet. Accordingly the Investigating Officer determined to drag the bed of the stream below the bridge, when almost immediately there was picked up a strong cord about 14 feet long with a large stone at one end and at the other a discharged pistol, the barrel of which fitted exactly the bullet extracted from the head of A.M.
The case was thus evidently one of suicide; A.M. had hung the stone over the parapet of the bridge and discharged the pistol behind his ear. The moment he fired he let go the pistol, which the weight of the stone dragged over the parapet into the water, but the pistol had struck violently against the parapet in passing over and so caused the injury observed. Experiment showed the trick to be quite easy and that the parapet was damaged every time. Subsequent inquiries disclosed that the pistol actually belonged to A.M., that his affairs were hopelessly involved, and that he had just effected an insurance on his life for the benefit of his family for a large sum. As the company did not pay in cases of suicide, A.M., had adopted this means to conceal the suicide and lead to the belief that he had been murdered.
As the astute Sherlockian (are there any other kind?) no doubt recognizes, Sherlock Holmes handled a similar case in October of 1900. It’s highly possible that he had read Gross’ work in the original German, perhaps in its first edition–or a later English translation–and thus knew to look for the chip in Thor Bridge….
*The selection appears in “Part IV–Particular Offences. Chapter XVI, Bodily Injuries and Poisoning.”