I'm not entirely convinced of the accidental circumstances.
1) The first thing when you wake up is think 'I think there is an intruder in the house, and hey my girlfriend is not in the best next to me'. So basic human intelligence is going to suggest the possibility that the person wandering around the house could be your girlfriend and not an intruder.
2) He shot at her four times, hitting her twice ...... he wasnt firing a warning shot or anything like that, he was shooting to kill even though clearly he could not have witnessed someone firing at him or his life being in danger because no other weapon was involved.
3) Here is a quote from a Devon and Cornwall police officer with regards to Valentines Day - 'we had anecdotal evidence from officers of an increase in domestic violence over the Valentine's Day period.'
So I for one am certainly not taking his account at face value.