Hi all,
Long time reader, first time poster.
From my very amateur perspective, I agree with posters like minor 4th that none of the evidence yet presented is really inconsistent with OPs version of events. However, I'm not sure that will prevent a murder conviction. On the contrary, I think the case is extraordinarily strong. Let's take a look.
1. OP fired through the door into the bathroom. This is beyond reasonable doubt.
2. OP was aware there was a person on the other side of the door. also beyond doubt.
3. OPs intention was to kill the person on the other side of the door.. This is important for premeditation. I think this is also beyond doubt. He fired 4 times using particularly deadly ammunition.
4. The person on the other side of the door posed absolutely no threat to OP.
5. The person on the other side of the door was killed. OP wanted to kill the person on the other side of the door, and he did so.
That's a pretty strong case for murder right there. The only thing missing is motive, and it's not clear to me that the prosecution needs to prove motive beyond reasonable doubt in order to prove premeditated murder. But let's look at motive.
Prosecution: OP was angry with the person on the other side of the door. evidence for this motive is quite weak. It seems to be based solely on the neighbours hearing screaming and arguing. Much of which can be explained away. Evidence against this is that there is no history of problems in the relationship or any trigger for such anger. That said, establishing such a motive is extremely difficult in the context of a romantic relationship.
Defence: OP was afraid of the person on the other side of the door. evidence for this is pretty weak too. It's based on a history of flipping out about intruders. Evidence against this is the fact that the person on the other side of the door posed absolutely no threat. That said, establishing such a defence is also very difficult, as there is absolutely no evidence to support that it was reasonable to be afraid of the person on the other side of the door, beyond paranoia.
So, I wonder if it is possible that the judge will find OP guilty of premeditated murder, which acknowledging that he may immediately regretted the act when he realised who was on the other side of the door.