....for at worst breaking into his house..
Sorry that is laughable and an indication that you don't understand SA. Which is fair enough. . unless you have lived there you won't understand it but don't kid yourself. If you live there and are burgled your chances of survival are not great.
I'm the only one of 6 siblings, who has not had a gun pointed to my head... Why? because I live in England. 
You guys can judge and speculate as much as you like. You can say ... You wouldn't do this.... You wouldn't do that... but the truth is you wouldn't have a f'ING clue what you would do because you cannot fathom the situation in SA. It's beyond your imagination. It's beyond belief. .. loads of people who have actually been murdered in their homes or businesses by burglars. and I mean a lot is people. And not Oh I heard of this guy that did this bullshit. But I am actually able to list people I know personally who have died like this. A LOT!
oh and they don't just kill you. You can be tortured first... just for fun.. This is very fucking real!!!
if you have ever actually been in fear of being murdered or raped..trust me.. logic goes out the window. you do what you need to do to survive and that would NOT awlays be the thing you would have done if you have had the time to draw up a plan. 
I would blow the fuckers away... and I probably wouldn't have stopped at 4 bullets either. I would probably have emptied the gun... ie 17 shots!
Whether he knew it was Reeva.. that I dont know but I do know that his defence is more realistic than Dewani who is imo totally guilty. You see his story works in England but SA they KNOW its bullshit because what he says is illogical. OP's story sounds like BS to the English but is valid in SA as this DOES happen there.
Please go read up on the Farm Murders in SA ... if you can stomach it..