I can visualize a balcony accident and Gpa losing it on Gma, and running with the child he "loved to death", but I can't see all family vehicles being left behind while going to get a rental vehicle. (Mind you, there's only 1 family vehicle in the drive ... maybe another in the garage??)
Plus, LE said to the effect that indications were that the family didn't leave of their own volition.
BBM
Brainstorming about what could lead LE to say they likely did not leave of their own volition (aside from forensic evidence like blood). There could be a million things but some ideas are:
A faucet was left running
Phone left off the hook
The phone line was cut (we think it was odd the brother came over after no answer on the phone... maybe the phone did not even ring)
fresh food left out/half eaten
stove or oven left on
shower left running
Could be so many things. Additionally, forensic indications such as the drag marks, any blood residue, etc.