Woah hang fire.
Mr Adam here was championing a box room exit via the twins bedroom.
Now he is championing my own theory!
I did suggest Nevill could have exited via the box room. It was 2 feet from his side of the bed & WHF does have 3 stair cases.
However the X's in the diagram show he was shot on the landing/stairs outside the main bedroom door.
Why would Bamber shoot a moving Nevill twice on the landing/stairs, then go back into the bedroom & shoot June 5 times?
This gives Bamber's biggest threat Nevill, a huge head start in a 1 storey building. Time to get downstairs and get a weapon.