YES!!! This is also my theory! I also think it is likely that AM may have intentionally instigated some type of conflict between JB and GB the night of the 26th, which resulted in JB's FB post and AB's Twitter post, plus may have had GB going to bed alone, and JB planning to sleep with the girls. I also wonder if AM had planned to have TM drive up during the night and then drive back with the girls, while AM stayed, thus being there when GB woke up. Do we know if AM was at GB's house that morning? I watched and never saw anything to make me think otherwise. What a great way to look innocent, if you had nerves of steel, and were a great liar. And, if you noticed on the store video, AM, who had already brutally murdered two people and had two little girls stashed somewhere, was cool as a cucumber.
I tend towards him having planned to kill AB and JB, arrogantly believing his plan was so perfect he wouldn't get caught. I think he had gotten away with so much in the past, including child molestation, that he was sure he would get away with this. He thought he had a few days. It was the perfect plan. He wasn't in a hurry. He didn't think they would ever look for bodies behind his house. He went to the store for a drink with his hair cut and his beard growing out, because he didn't think anyone suspected him. At that point he thought he still had time and his plan was on track. He had food and supplies and would quietly slip out of town with the girls "shortly".
AM=SOCIOPATH
My theory only