My guess is that the whole scene played out with a violent confrontation in the garage, moving to the yard and down by the water. The "killer" never entered the house. RD never left the garage.
I am with you on this one. I think these folks may have been held hostage in their home for quite awhile before all the violence started. Most likely in an extortion attempt to get them to cough up some money, and a lot of it. When this tactic failed, Mr Dermond was killed in front of his wife to coerce Shirley to cooperate.
The fact that nothing seemed to be missing from the home suggests to me that the perps came in and left via the water. How much "stuff" are you going to load into a small boat without it being totally obvious to any passerby or witness ?? Any small boat that is crossing the water that is loaded up with household goods and personal belongings is going to draw a hell of a lot of attention when it pulls up at a dock.
No, this was about money. Someone thought these folks were loaded to the gills with it and were banking that they had a whole bunch of it stored around the house somewhere.
Mrs. Dermond may or may not have been loaded into the boat in an effort to terrorize her into submission. If she got to yelling and hollering and tried to draw attention to the situation, then most likely she was sliced and diced and dumped overboard to quieten her down. Of course the very same thing could have occurred right down at her own dock. I'm sure her husbands head is in the water as well, it just hasn't been discovered yet.
Either way, the perps ended up committing senseless murders and probably got absolutely nothing out of it. The fact that so far they committed almost the perfect crime, is just sheer luck on their part.
The two guys that kidnapped Holly Bobo seemed to have committed the perfect crime too, and they are just a couple of whacked-out meth addicts.
Total losers who contribute absolutely nothing to society, but they pulled off a crime that had everybody stumped for over 3 years.
This will turn out to be very much the same thing.