Following up with Jo in Calif and Rhyolite, Some thoughts:
On the issue of a fatal head injury, I am visualizing the discovery of Mrs. Dermond. The two fishermen saw something, determined it was the body they had been watching for, and did what? Would they have, regardless of the awful scene, been unable to resist taking a few photos with their phones? Then, after calling the law, they waited and watched. I would think when Sheriff Sills got the call, he grabbed his respirator and went.
Surely per procedure, no one would have disturbed the scene. I picture Sheriff Sills slowly going in a circle around the corpse, taking scores of photos and using a voice recorder to make notes as he went, being very careful to preserve evidence. Then, he would get closer and closer, and finally to examine very closely the condition of every part of the corpse, perhaps especially the head. If, and this is a big if, he could later say there were no "glaring" signs of trauma, and he spoke truth, the fatal injury was relatively less dramatic than if the victim were struck with a vicious weapon, and struck many times in many places.
So, the fatal blow must have been, for lack of a better term, "soft", and perhaps not meant to be fatal?
The autopsy results were death due to blunt force trauma. In the case of Mrs. Dermond, it seems she was not killed by an attack so viscious that there were injuries easily seen by a trained police officer.
It would be useful to know if Mrs. Dermond was struck one time, many times, from the front, from the back, from the side, etc. If she was struck once from the back, and not particularly hard, she may have never known what happened. And is it possible that the blow was not necessarily meant to be fatal?
It seems clear that an equivalent type of blow could have felled Mr. Dermond resulting in almost no obvious cause of death. The killer could then have done as he pleased. No noise and all the time necessary to "work" with his favorite tools...
