This is pretty much my current theory as well. The guy either had evidence or strongly speculated the 3 other individuals were a major reason why the relationship was ended. Says the breakup was amicable to everyone for the sake of his own pride while developing deep resentment for everyone he thinks was involved. Perhaps he learned E was staying over on short notice and knew he had to act because this was probably one of the last times they would all be in the house together which could possibly explain the sloppiness in terms of all the evidence left behind. I think he left the two surviving roommates alone because he knew they weren't involved in the relationship breakup. May have called his own phone from the victims phones as a poorly thought out attempt at creating an alibi for himself. Lives nearby so it wouldn't be strange to be seen in the vicinity of the house. Also gives easy way to monitor the house. This would also explain why no dog barking as he is part owner. All IMO of course as always.
