Just write down the license plate. What more do you really learn by following them. You don't know they are going home, and when did get there, you still wouldn't know it was their house.
Until you saw Papa with the gun, then you'd know.
The story is a bit weak on the events at that point. That's were the rubber will meet the road during the trial. If the father was merely on his own property with the pistol, or maybe with a concealed pistol,and the guy threatened him, that's one thing, but if when the guy just showed the father shot him, that's quite another.
The story says the guy made a second pass. Now if I saw Pop in the driveway with a visible semiautomatic handgun, I don't think I'd be making another pass at the house.