Rumor has it Ethan was the target all along. Ethan and his GF were killed first. The killer must have heard movement upstairs and went up the stairs to find the two girls. He killed one and the other tried to escape and screamed. This freaked the killer out and he threw her on top of her deceased friend and slit her throat to quiet her. He was freaked out though and so he ran out the door and was seen on cameras from an A&W store in the area in the white car shortly after the time some of the neighbors cameras picked up the scream from the murder house. This is what I've seen on a pretty reliable site.
I don't think he was alone. A cops bodycam captures about 4 people running from direction of murder house at the time of murders while conducting a traffic stop nearby. The 4 people captured in silhouette form with murder house in background.
We should know more after News Presser.