So I was thinking about it some more. I think it's more likely the perp parked next door with his car. Because first of all, he had to drive by there several times before, to learn the house layout. Then he had to probably drive by there, one or two times before, that same night, to make sure nothing unusual was happening there. And he wants his car nearby for a quick getaway, just in case.
So we know the empty lot next door was owned by one of the REM members. We should look at somebody who's acquainted with the REM member, and or knows that guy's schedule. For example someone who would be aware of when he's playing a show, or traveling. Because he knows, that if the guy is away playing a concert a certain night, then he knows he can go park there at his lot without any problems. I don't know what type of parking they have there on that lot, if it is some gravel road that's deeper in and hidden behind some trees, that's even better. That would be the lure for him.
This would be one good way for the perp to notice the Dermonds. Either he was invited to a party there at REMs lot, or maybe he used to vacation there and he heard about it through local legend, that the band member had a lot there. And one day, he drove by out of curiosity to go look at. Perhaps he was already interested in using it as a parking lot to commit crimes. And was looking around at who was next door. And he noticed the Dermonds there. He thought they were an easy target, and he made his plan. He must have parked in that lot enough to notice the Dermonds schedule too.
Now I don't know what type of boat they had lying around there nearby, one of the neighbors, who were not there. He could have gotten a boat there.
Or he could more likely I think, put Shirley in his car. And he drove her maybe to the campground near the dam. He put her in a boat there, and then just had to go out a little bit out in lake to dump her body, and then come back. He could have even just used a rowboat for that short trip. Because I think him going miles on a boat, in the open lake, is a little bit insecure for him. He's always safer in a car. So he would want to minimize his time on the boat. Perhaps he had already checked out a boat there beforehand. One that he knew would not be seen by anybody. Of course he probably did this late night.
I mean apparently he stayed there overnight, so he had plenty of time to go back and forth.
Of course another element of this case is the perp probably knew lock picking as well. That's how he was able to get into the house through unforced entry. So we should look for somebody in the area who was accused of knowing lockpicking, and who maybe has an arrest record of trespassing in other people's houses. A connection to the music industry here would also be good