Except the deceased is Reeva, who wasn't in the cubicle as far as OP knew at the time. The argument also suggests that OP was not in a reasonable state of mind (as opposed to being mentally incomplete by) and was negligent at the time...not that he fired with intent to kill, but that he should have realised that his actions could kill...there is significant difference.
But why else would a sane man fire four bullets blindly through a door behind which he knows someone is standing/sitting behind? He intended to kill the person behind that door. There is logically no other explanation.