JB would not have left WHF unscathed if it had been him as the murderer. At the least,his father would definitely have left his mark on him in some way but because it had been a woman,Sheila,Nevill would have been less likely to have landed out.
Judging by the many reports of JB having had his father in tears and not being the perfect son etc, you'd have thought that Nevill would have been well prepared for any eventuality that occurred involving JB ??
At well over 6ft and a well-built man it's rather surprising that Nevill,who'd been in the forces and well versed with " the enemy " wasn't on his guard ? Such as the removal of all guns and secured in a tightly locked cupboard/cabinet for a start.