I have also looked at things from both sides - however, I have NEVER quite got my head around him not calling 999. I may have made excuses for it - but that's all they were. I can't see how any one would be suffering from shock with the amount of information he had. At that point, nothing had really occurred and he supposedly knew the rifle wasn't loaded anyway.
But if he had planned everything so meticulously why did he make himself look more stupid by not calling 999 ? If it was a timing thing then just wait a bit longer and do the obvious thing ?
You have claimed he wanted to set up the most dangerous scenario so the police would NOT go in and establish the T.O.D. So calling 999 would make more sense . The was he worded it originally was she had just got hold of the gun . So no indication of any shooting at that stage . But when the raid team were eventually called they were told it was a shooting incident ? Which the police had not established.