If Pistorius is found guilty of this charge, he will face a mandatory life sentence of a minimum of 25 years in jail. Mitigating factors could reduce the sentence.
According to the defense, he mistakenly shot Steenkamp thinking she was an intruder. The prosecutors argue he intentionally shot Steenkamp after an argument.
Murder
This charge differs to premeditated murder because Judge Masipa would need to be convinced that - although Pistorius did mean to kill whoever was behind the door - he did so without any prior planning.
This charge carries a sentence of up to 15 years. Judge Masipa can decide on a shorter sentence if she finds that Pistorius has shown sufficient remorse.
Culpable homicide
Photo / AP
For this verdict, Judge Masipa must been convinced that Pistorius did not intend to kill Steenkamp out of rage, but that he was motivated by fear and believed he was shooting at an intruder.
This charge also carries a sentence of up to 15 years in jail. Or he may not have to spend any time in jail if Judge Masipa decides that his actions were reasonable.
Factors that could lead the judge to believe Pistorius acted reasonably include his anxiety, South Africa's crime rate and the pressure he was under as a celebrity.
Acquittal
If Judge Masipa is convinced Pistorius acted reasonably and in self-defence, he may be acquitted.
However, even if this is the decision, Pistorius still faces a raft of other charges which may still carry a jail sentence. He is accused of twice discharging a firearm in public and illegal possession of ammunition.
After the verdict
While some may think the case will wrap up with Judge Masipa's verdict, there is the possibility for either the defence or prosecution to appeal.
Where's the jury?
Jury trials were abolished in 1969 while South Africa was under apartheid. There were fears of racial prejudice by white jurors during this time.
Who is Judge Masipa?
Judge Thokozile Masipa, 66, has sat on a dais in red robes throughout the televised trial, rarely interrupting the drama unfolding below as the prosecutor sought to prove that the Olympic athlete murdered girlfriend Reeva Steenkamp and defense lawyers argued that the shooting was a terrible mistake.
Her cryptic demeanor, likely meant to project neutrality during contentious proceedings, masks the rich personal story of a former social worker and journalist who became one of the first black female judges in a country that jettisoned white rule in 1994.
Some experts have pointed to Masipa's record of tough action against criminals who victimized women as indicators that she would not be easily swayed by Pistorius' assertion that he shot Steenkamp through a closed toilet door on Feb. 14, 2013 by mistake, thinking there was an intruder in his house. Yet they also describe her as a good listener and a dispassionate analyst of facts.
For some South Africans, Masipa is a symbol of accomplishment in a country where poverty and unemployment block progress even though all-race politics replaced white minority rule in a euphoric but troubled transition.
"From our historical background in this country, it is very important that young black people see role models that are positive," said Kabelo Seabi, a Pretoria lawyer who teaches criminal law. "I'm sure that a young female person that's sitting anywhere in South Africa ... would be looking up to her and would wish that, if they were to study law, that they would be able to reach that benchmark that she has set."
In the rare instances in the Pistorius trial when her personality has shone through, Masipa has been stern, chiding the prosecutor for harshly questioning the double-amputee runner when he testified in April. And she lightened the mood in the wood-lined courtroom when she joked about making lawyers work "after church" on a Sunday.
Seabi described her as a competent judge who gave "latitude" to defence and prosecution arguments. Masipa will not "decide the matter on her own" because she has two legal assistants, Seabi noted.
"There is a remote possibility of the judge going one way and the assessors going another, and the decision by the majority is the one that will stand, on the facts," Seabi said. But, he said, only the judge decides on questions of legal principle.
Masipa studied social work and later worked as a reporter for The World, The Sowetan and other South African publications, covering township life at a politically tumultuous time. Under apartheid, she was arrested during a protest against the detention of media colleagues, according to South African reports.
Sekola Sello, who worked with Masipa in the media, said he has closely followed the Pistorius trial and that the judge was exhibiting the same "level-headedness" that he remembered in her character decades ago.
In 1998, Masipa became a provincial judge on a bench that was still heavily populated by white males. Last year, she sentenced a serial rapist to 250 years in prison. In 2009, she sentenced a former police officer to life in prison for fatally shooting his wife after a dispute over separation terms. She has ruled in favour of squatters who resisted attempts to evict them from a Johannesburg building and said authorities should help them find alternative lodging; and ruled against a former head of Eskom, the national electricity company, who alleged he was illegally dismissed.
- nzherald.co.nz, AP