The day this broke somebody was on who said they were ".22 automatic" casings. I haven't heard anything since.
If they found such casings, they could have come from a semi-auto rifle or pistol, or any kind of a .22 rifle for that matter, but unlikely from a revolver unless there was a 'reload' involved.
The same source said there were guns in the house but they were locked in a gun safe.
Theory? It sounds to me the husband was confronted at the truck, was bleeding and ran back into the house, followed by the assailant(s). There apparently was a blood trail from one to the other. The family reputedly kept the doors locked most of the time and especially at night, so he must have gone out to the truck for whatever reason and left the front door open when he did. Then he was attacked and ran into the bedroom, where he was subdued. It must have happened so fast nobody could call 911, much less get the gun safe opened. JMHO.
It's too bad he didn't take a gun with him.