I'd be interested to know if the driver of the truck that was stopped shortly after the BOLO was issued lived nearby (say, within a block or so of EB's home), and if so, did anyone else live in the home who might have had access to that truck earlier that morning? (And in the middle of the night before.) Could it be that there was something about the Barazza's living nearby that irritated someone who was a hothead (or who had a propensity to drink or use drugs to the point of losing impulse control when angry) and who also had access to a gun?
For example: I see that EB and SB had a dog. Was the dog out front, or in the house, or left in the backyard while EB and SB began setting the garage sale up? Did the dog frequently (or even occasionally, but recurrently) bark outside, where it could be heard down the block or in homes on the cul-de-sac behind the Barazza's home? Were any folks in the neighborhood aware of anyone who was getting especially testy about it? When EB and SB walked their dog (or let it loose, if they did that), did they pick up the dog's waste? (Could a photo of dog waste "left behind on someone's lawn for the umpteenth time" have been what the shooter was showing EB before shooting her three times, and then a fourth?).
Dogs defecating on neighbors' and HOA-common-area lawns is a BIG source of recurrent, and increasingly angry complaints on a social media site used among neighbors where I live.
If there was a recurrent problem about which a neighbor was getting increasingly irritated, that could explain the truck's presence in the middle of the night before as well as the morning of the murder. Maybe anger and hostility were building in someone whose only connection was proximity.
To me, the shooter looked like and seemed to move like an adult woman and her rapid approach up the driveway looked like it could have been driven by anger.
Edited for spelling.