clearly we need more facts and there is a lot of conflicting info circulating.
I've just read in one of the online newspapers that the bathroom involved was ensuite. If this is the case, how could he get the gun (kept in the bedroom) and shoot at the ensuite bathroom door without noticing that his girlfriend wasn't in the bed?
And why would she have locked the bathroom door if she was simply using the loo in the early hours - I'd be lucky to shut the door properly.
Re the balcony door being open until the wee hours, that is odd for someone who is so paranoid about safety in home. Paranoid enough to fire 4 rounds at a shut bathroom door without knowing the whereabouts of their loved one. It is quite common to use the bathroom in the night. But it is summer down there and it is hot - so perhaps he did sleep with the balcony door open.
Was balcony door in the bedroom? That would make sense re leaving it open due to heat. If it was elsewhere in the home, then I think that seriously weakens his 'paranoid about being attacked in the night' position. If you were that worried then you wouldn't leave a living room balcony door open while you slept in another part of the house would you?
I really hope for everyone's sake the SA police and forensic team do a proper job here. Surely the truth can be revealed forensically? There must be a lot of GSR & blood splatter etc telling the tale. I like to see a floor plan of the house & know where exactly the bathroom and balcony were located.