Based on the version of events provided by Pistorius and his lawyers at the bail hearing, the disputed element of the crime will be fault. You can only be found guilty of murder if you unlawfully and intentionally killed another person. You can be found guilty of culpable homicide if you unlawfully and negligently killed another person.
There is no dispute that the killing of Reeva Steenkamp was unlawful as it would be impossible to argue that Pistorius acted in self-defence (or private defence, as it is known in law). You can only rely on self-defence to exclude unlawfulness if an attack on your life (or the life of another), on your property or other similar interest has commenced or is imminent. This is an objective test, so where no attack actually occurred, one cannot rely on self-defence to justify the killing of another person, which you thought was necessary to defend yourself. No such attack occurred or was imminent in this case. (Whether the common law should be developed in line with the values in the Constitution to restrict the right to kill others in defence of your property, is an interesting question, which I cannot discuss here.)
