I know that over 3 years and 8 threads, a lot of these details have been discussed over and over again, but it can never hurt to revisit, and rethink these details to bring ideas to the forefront again. So I hope it's ok if I post some of my crazy brainstorming (mostly accomplished in the wee hours of the night/morning when my brain is probably not as sharp as it could be). With respect to the attacker (official LE and crime writer/blogger profiles aside - and all just my opinion):
1. A random crazed predatory psychopathic killer (not meant to be any kind of accurate diagnosis/label) who didnt know AG and wasnt necessarily from the area, randomly selected AG on the spur of the moment and just lucked out that she happened to be elderly and alone. Ambushed and attacked AG in her garage while the dogs were locked in the house and barking/freaking out. Not sure how the attacker then entered the house to take items away that were later left strewn around outdoors on the property, OR how the attacker left the scene without leaving obviously distinguishable DNA/prints/other forensic evidence (presumably, since I personally would assume if any obviously distinguishable evidence was left, then Scott would have been a no match, rather than inconclusive). This type of a random attack seems unlikely to me in such a remote, rural area. The attacker would have to get there (car/bike/on foot) in the winter and get around the open space surrounding AGs home undetected. Getting away from the location would be difficult without being seen or heard imo. Not to mention all that messy evidence.
2. A crazed predatory psychopath who IS from the area, or knows/cased the area, and selected AG specifically because she is a single older lady living in relatively private seclusion. Planned out the attack carefully watching AGs habits, the dogs, etc, and timed the attack, watching and orchestrating it so AG was already in the garage, and attacking and murdering AG while the dogs were inside barking and freaking out. Less likelihood of leaving obviously distinguishable DNA/prints/other forensic evidence due to pre-planning. Still unsure about how the killer would then enter the house to obtain the items that were taken, with the dogs in there. This seems more likely than a completely random attack though. If it was a random/not-known-to-AG attacker, but a planned out attack, then the killer would have figured out what time of the day/night would be best, how to get on and off the property undetected, and how to prevent leaving evidence behind, or leaving less evidence behind.
3. Take either of the above scenarios and insert a friend/acquaintance of AGs" who is a crazed predatory psychopath and carried out one of the two scenarios.
4. A friend/acquaintance of AGs who was there for a visit and suddenly snapped due to some beef or perceived slight/insult/disappointment, and in a rage attacked AG. Just lost it and went ballistic and murdered her. However, even if this person were known to the dogs, after they had carried out the heinous attack on AG, there would be no getting inside the house with the dogs loose in there after they had heard this happening to AG. Also, again there is the issue of the unplanned, messy attack and DNA/other evidence being left/taken.
5. A friend/acquaintance of AGs who had a simmering beef with her, and had been stewing over it for a while, building up anger, determined to sort it out. They make arrangements to go to her home for a visit and organize things in a way that allows them to carry out the attack and theft. Such as going inside to place something in the house for AG, or going to use the bathroom. While inside they discreetly pull shut the door to the room where the dogs are hanging out inside the house, or slide the gate across the kitchen entrance-way, for example, maybe also at this time somehow sedating the dogs, before stepping back out to the garage where AG is waiting having a smoke. Then they carry out the attack, go inside and take the items, do whatever, and leave.
Maybe the perp had ALREADY been inside the house prior to the murderous attack, and had either already ensured that the dogs were safely out of the way, OR had already taken the items, before killing AG.