I don’t understand why a killer would kill BS elsewhere in the house and then have to drag him to the side of the pool. It would be a lot simpler to just force him walk to the side of the pool,and kill him there.
If I was the killer, my strategy would be to use lethal force on Barry at the first encounter, by surprise, to eliminate the risks of him:
-escaping
-calling 911
-making noise that neighbours might hear
-struggling with me (and potentially injuring, exhausting, or killing me)
-leaving loads of DNA and material evidence.
The longer he was alive, the greater the risks of one or more of these occurring.
Dragging a dead body might be exhausting, but it's more reliable than trying to position an alive, struggling, yelling male in a basement room with a large body of water in the middle surrounded by a perimeter of decking. If Barry had been alive and struggling, the chances of him or both going into that pool are not zero.
The immense risk the killer took was to position both bodies together, in a room that was likely a different location from where he (I assume) killed them. That is, to me, non-sensical, unless he had a good reason, he was extremely confident that no one would enter the home, and he had the strength and stamina to position both bodies there. Even so, the likelihood of leaving DNA or other evidence grew the more he moved about the house with bodies. It did not seem to be an "in and out" methodical killing because of the positioning of those bodies.
I don't know what to make of that. I find it bizarre. I couldn't conclude from my interpretation that it was a hired job or a person known to them--there's just no way of knowing.