As the person in the bathroom hadn't threatened him, it's not really self defence either is it.
South African law gives far more leeway to the use of force in self defence than many other countries. Anyone can respond with force if their life is in danger.
The attacker does not necessarily have to be carrying a weapon: if you fear injury or death, you can use the most extreme means, including killing the assailant.
There is no balancing of weapons. If, for example, the attacker is carrying a knife and his target happens to have a firearm, the intended victim would be entitled to shoot that person dead.
South African law also states that you can defend somebody else if there is a possibility of serious injury or death. You are entitled to intervene and even kill the attacker. You do not have to be in a family or any other kind of relationship to the victim.
If somebody breaks into your house, you are entitled to kill that person under certain circumstances. If the burglar runs away and you kill that person anyway, you could be exceeding the bounds of self-defence. If, however, you are faced with a situation where you fear for your life or safety, you would be entitled to kill the intruder.
South African courts understand that these scenarios happen very quickly, usually at night. A householder cannot sit down and decide objectively exactly what should be done. You could reasonably expect any intruder to be armed and capable of doing you harm. The courts tend to accept a broad definition of self-defence.
http://www.telegraph.co.uk/news/worldnews/africaandindianocean/southafrica/9871195/Oscar-Pistorius-m...
