sherlock, masters Scipio USMC and John are no more qualified to offer opinion than you or I . Plenty of folk read these forums so if there's any mileage in my theory it will be seized on and developed to its full potential by those who are qualified
1) I could qualify as a weapons expert based on my training. I have more expertise than the average person which is all that is required to be considered an expert.
2) The experts in this case assessed the casings among other evidence indicates the shots had to have been fired from the foot of the bed to the doorway with the gun aiming INSIDE the room.
3) The experts assessed the trajectory of the wounds being to Neivll's left profile
4) All one needs is half a brain to know that it is impossible for the left profile to be targeted if someone is on the stairs with their left side facing a wall.
5) All one needs is half a brain to know that it someone is looking at your back they can't shoot your left profile.
6) All one needs is to not be blind to see the ejection port is on the right side of the gun and understand this means the casings are ejected to the right.
7) All one needs is half a brain to recognize that if the gun were aimed at the doorway that the wall with the window would be to the right of the weapon.
8) All one needs is the ability to know how to read to know that not a single casing was found near that wall where the casings would have been if the gun were aimed out the door.
Your claims have been thoroughly refuted and been shown to be totally unsupportable.