the instant death just points to a shotgun blast to me. I don't want to be too graphic, but will say I had a family member shot in the head with a shotgun and they couldn't even be embalmed because of the extent of damage done. even if the aorta was hit there would be a short time before death, a ruptured aorta from a car crash might live long enough to make it to the hospital. a severed brain stem would cause instant loss of awareness. IMO the human body will try to stay alive when it really shouldn't be able to. the blood circulating would already be oxygenated and I would think that would have to be exhausted before death firmly takes place. that's why a ambulance would have been called unless it was VERY clear there was no hope at all IMO. I do not think this is a simple gunshot like is seen on tv. there had to be massive damage for no attempt at life saving intervention to even be tried. if they tried and called it after 3-5 min that would be one thing. absent massive damage LE had no way to know if they were firmly expired or if their hearts had just quit.