I think it escalated from this .....
"Mr Lynn told him he was speaking nonsense."
I also think it is possible that Russell was shot in the back as he was walking away from Lynn after a confrontation.
Then Carol was shot, cowering in fright, near their campsite.
I am thinking that Lynn had his shotgun nearby, ready to go night hunting. Because he said he used his shotgun in darker areas when hunting (but didn't say he went night hunting).
Lynn appears to have had a dominance and rage issue, according to a report of domestic violence when his first wife was still alive.
Greg Lynn admits covering up the deaths of two campers and disposing of their bodies, his lawyer says, but insists he is innocent of murder.
www.abc.net.au