Yes. I cannot rationalize an irrational mind, but the left-behind sheath says a lot, IMO. Clearly the sheath was not attached to his belt, so WHY did he bring the sheath in with him? He thought to wear all black and a mask, he thought to turn off his phone, he thought to leave a PA license plate on his car, but once he got to the house and it was going to happen, his common sense betrayed him. He should have left the sheath in the car.
Once the crime was over and he was back home, common sense kicked back in...changed his license plate, used gloves everywhere he went, put trash in neighbor's cans, etc.
He was definitely in a "zone" as I've seen it said, during the killings. Freaking scary.