He paused for a moment; but the inspector made no comment.

"The two greatest factors in the suppression of crime," continued Malcolm Sage, "are photography and finger-prints. Both are in use at Scotland Yard; but each in place of the other. Finger-prints are regarded as clues, and photography is a means of identification, whereas finger-prints are of little use except to identify past offenders, and photography is the greatest aid to the actual tracing of the criminal."

Malcolm Sage never failed to emphasise the importance of photography in the detection of crime. He probably used it more than all other investigators put together. He contended that a photographic print established for all time what the eye could only dimly register for the moment, with the consequent danger of forgetfulness.

As the links in a chain multiplied, it was frequently necessary to refer to the scene of a crime, or tragedy, and then probably some important point would crop up, which the eye had not considered of sufficient importance to dwell upon. By then, in the case of a murder, the body would have been removed, and everything about it either re-ordered or obliterated.

Malcolm Sage proceeded to stuff his pipe with tobacco which he drew from the left-hand pocket of his jacket. He had discovered that a rubber-lined pocket was the best and safest pouch.

He picked up a third photograph and laid it beside the others. It was a print of Mr. Challoner's head, showing, marked in ink, the course of the bullet towards the left of the frontal bone.

"A man shooting himself," began Malcolm Sage, "places the pistol in a position so that the muzzle is directed towards the back of the head. On the other hand, anyone approaching his victim from behind would have a tendency to direct the muzzle towards the front of the head. That is why I got Dawkins to take a photograph of me holding the pistol to my head and of you holding it from behind. These photographs will constitute the principal evidence at the trial."

Sir James nodded. He was too interested to interrupt.

"On this enlargement of the wound," continued Malcolm Sage, "you will see an abrasion on the side nearer the ear, as if the head had suddenly been jerked backwards between the time of the muzzle being placed against the temple and the actual firing of the shot."

Thompson leaned across to examine the photograph.