Treelights might know. They posted the information on the size of the garage. If I remember correctly there were blueprints posted of the home early in the case.
See more at: http://www.atlantamagazine.com/grea...d-sills-chases-a-killer/#sthash.uVW8KYto.dpuf
I don't know. Sounds like he entered the side door - the one with the steps beside the garage ? and then once in the kitchen there is a door into the garage. Strange to have a front door open to your dining area. We have only one entrance to our garage besides the obvious garage doors and it is a door from the kitchen that opens to the garage. However, the garage doors could have been open at the point all this went down and the killer shut them once he had silenced the Dermonds. Maybe that's why the neighbors didn't enter the house sooner because the garage doors were down and that means the Dermonds were not home.
Looking at the photos on Zillow, I can't even count how many exterior doors there are. I would guess that they all had deadbolt locks not the kind with just a button that you push or turn to close and lock on the way out. Open floor plan, strange floor plan with visibility completely through the house from the front door to the back. Cannot see the kitchen or if someone was sitting in the kitchen maybe at the bar from the front door, though. There is a door from the porch to the kitchen and a door from the back deck to the kitchen. My guess is that the neighbors came in through the porch. They either had a key or knew where one was hidden. Mr. Neighbor checked the garage through the unlocked garage door to see if a vehicle was gone and found Mr. D.
So, the perps could have been let in or forced their way in through the front, did whatever they were there to do, and left through the garage door, letting it down on the way out. Front door still unlocked, and house door to garage unlocked.