We have the shooter at the main doorway in possession of a loaded gun...
June Bamber, alone in bed - the shooter tip toes into the bedroom until they are just inside the doorway, they see June sleeping horizontally upon her side. The shooter takes aim, and within a matter of two or three seconds a total of 5 shots are fired at her body...
The shooter, either then thinks or believes they have killed June, or they are worried that Neville Bamber might have returned to the farmhouse, and heard the shootings, so the shooter leaves the main bedroom still with a maximum of 6 bullets still loaded inside the weapon. They go downstairs in the expectation of being confronted by Neville Bamber, but it turns out to be a false alarm, so the shooter returns back upstairs, by which time June has managed to get herself out of bed, and had actually walked around the bed, and back to her side of the bed again, only to be shot twice more by the shooter, shots which effectively killed her immediately...