If that was his plan then he must be completely mad. Too many 'What if's...':
Somebody saw him on the road.
The dog barked and alerted Neville.
Someone heard him climbing through the window.
Someone was awake at WHF and called the police.
Neville had unloaded the gun and put it away.
He was overpowered by Neville.
Sheila locked herself [and her children] in the bathroom or another room.
Sheila refused to cooperate and allow herself to be shot.
He left a tiny amount of blood on the window, the bike, his clothes.
JM went to the police.
Et Al...
All these were minor obstacles as far as Bamber was concerned, pre massacre.
He was committing the massacre between midnight - 2.30am. The perfect time for an execution.
No one would see him ride across the fields at that time. DB said it passed no dwellings.
There is a thread on the dogs. Crispy was certainly not a guard dog.
The window had been loosened beforehand, or had been left open by Bamber when he went to supper. So the downstairs noise would be minimal.
There was no reason why anyone would wake. The rifle with the silencer on is almost silent. There was a possibility someone was already awake, but that was a chance he was prepared to take at that time period.
Everything was seconds away from going exactly to plan. Neville woke seconds before getting fatal shots while he slept. This was because Bamber fired into June first.
Bamber was not worried about Julie, post massacre. He assumed he had left no forensic evidence and he could keep her sweet for a few months. But he soon tired of her, and her of him.