on the flip side I imagine Shelia had never tried suicide with a rifle. But it doesn't take a lot of working out does it.....
His first shot was not bad either. He made a quick decision to fire the second shot.
Sheila may have been breathing & even groaning. The pain for her would have been horrendous.
Unlikely she would have still been alive after 1 shot when the police entered WHF. But Bamber did not know that. He wanted to leave WHF with everyone dead.
In hindsite it was a mistake firing the second shot. Inheritance killers do make mistakes, which is why they get caught. Bamber was not smarter than the others.