Here is another theory of mine. Maybe DG stopped by the estate sale earlier in the day and looked around to see if there was anything of interest. He could have arranged to come back later to pick something up. He could have had a chat with AL that ticked him off for whatever reason. He could have stopped by just for a chat.
We don't really know the essence of their relationship. Sometimes people get into petty arguments yet still remain outwardly civil, especially when they are family, even tho deep inside they hate each other. We don't know if the petty argument about a patent was old news or still a fresh and open wound. We don't know if there was something new to add to DG's frustrations with AL.
Anyhow, I imagine that DG was in the area and possibly visited the home before 10PM that night. His truck was seen SEVERAL times as per LE.
The front of the home is wide open and if the neighbors stepped outside they could see everything that was going on in that driveway.
https://www.google.com/maps/@51.019...ata=!3m4!1e1!3m2!1smjdDPdowu0QJO3KIaGtwrw!2e0
Was this a silent crime? How could it be? He must have had some cojones to bring 3 people in the front of the house like that. He could have been caught any time.