Police crime scene work seems amateur and if they have nicked watches and moved objects around that could help Oscar get off with murder as tampered evidence may weaken prosecution.
I don't think it will have a bearing, well I hope not.
The law and rules of engagement over their are very strict and well laid out. Your life or that of someone close to you has to have their life in immediate danger for you to pull the trigger, you should never become the aggressor which in this case, a noise in the bathroom to an unknown, possibly unarmed trespasser does not warrant under any circumstances for him to discharge his weapon.