What are the findings of Mr. Wood in Valley of Fear?

From the text:

The doctor knelt beside him and held down the hand lamp which had stood on the table. One glance at the victim was enough to show the healer that his presence could be dispensed with. The man had been horribly injured. Lying across his chest was a curious weapon, a shotgun with the barrel sawed off a foot in front of the triggers. It was clear that this had been fired at close range and that he had received the whole charge in the face, blowing his head almost to pieces. The triggers had been wired together, so as to make the simultaneous discharge more destructive.

What have you got there, Dr. Wood?”
It was a good-sized hammer which had been lying on the rug in front of the fireplace—a substantial, workmanlike hammer.

The dead man’s right arm was thrust out from his dressing gown, and exposed as high as the elbow. About halfway up the forearm was a curious brown design, a triangle inside a circle, standing out in vivid relief upon the lard-coloured skin.