Prosecutors say Pistorius murdered Steenkamp following an argument in the early hours of Valentine's Day in 2013. The track star says he mistook her for an intruder.
What is Oscar Pistorius charged with?
In addition to being accused of the premeditated murder of his girlfriend, Pistorius also faces a gun charge related to the killing, along with two additional gun-related charges for two separate instances of firing a gun in a public space before the killing.
Why is Pistorius facing a judge rather than a jury trial?
South Africa abolished jury trials in 1969, while the country was under apartheid, due to fears of racial prejudice by white jurors. Pistorius is being tried in Pretoria by Thokozile Matilda Masipa -- the second black woman appointed to the bench since apartheid ended.
What are the sentencing guidelines for premeditated murder?
For premeditated murder, the mandatory sentence in South Africa is a life sentence, which in practice is 25 years unless someone can prove extraordinary circumstances.
Extraordinary circumstances could include a combination of number of factors: for example, that it was a first offense, the age of the person and in Pistorius' case, his disability and the impact this could have had on his actions.
James Grant, senior lecturer in criminal law at South Africa's University of the Witwatersrand, said if the court accepted the prosecution's case -- that Pistorius chased Steenkamp into the bathroom and "hunted" her down -- the track star's defense team would be hard-pressed to convince the court that there should be any considerations that should override the repugnance that should be felt.
What happens if Pistorius is found not guilty of premeditated murder?
If Pistorius is found not guilty, he could face a lesser charge of culpable homicide, which is based on negligence.
Pistorius is not claiming self-defense; he is claiming to have been mistaken about his need for self-defense. He is denying that he intentionally unlawfully killed Steenkamp. Grant said the defense boiled down to Pistorius saying "I made a mistake."
If the court were to rule that the mistake was unreasonable -- based on what an objective, ordinary South African would do in the circumstances of the accused -- he would be found guilty of culpable homicide.
Grant said he would probably expect a court to conclude that it is unreasonable to fire at anybody through a closed door regardless of whether they were an intruder, because of the value of human life.
"I'm expecting that if he beats the murder charge, he is in very grave jeopardy of being convicted of culpable homicide," he said.
What's the sentence if Pistorius is convicted of the lesser charge of culpable homicide?
If Pistorius is convicted of culpable homicide, no minimum sentencing legislation would be triggered. "Courts are able to exercise their complete and ordinary discretion," Grant said.
This means, theoretically, Pistorius could get a non-custodial sentence if convicted of culpable homicide. Grant said there had been examples of people killing a loved one accidentally where they had avoided jail.
If, however, the court took a view that Pistorius had been grossly negligent, Grant said, he would guess the runner could be jailed for up to 15 years.
What about appeals?
If Pistorius is convicted, he can appeal the verdict or the sentence, potentially to the supreme court and even eventually to South Africa's constitutional court. Whether he gets bail while waiting for the appeal to run its course would depend on what he was convicted of.
If the star is found not guilty, the state can also appeal, but on more restricted grounds.
The right to appeal depends on whether, based on the facts of the case, the initial judge or magistrate believes a different court could possibly reach a different verdict.
South Africa's highest court, the constitutional court, used to be only for cases regarding constitutional matters, but a recent act of parliament broadened its remit.
Would Pistorius be given special treatment in prison if he was convicted and jailed?
CNN's team in Johannesburg understands the double amputee would not receive special treatment, with even blind prisoners being placed with sighted prisoners in South Africa.
But, ahead of his release on bail last year, the African National Congress Women's League said the athlete had in fact benefited from special privileges, adding that his family could visit him outside visiting hours, unlike relatives of other inmates.
What is the reputation of South Africa's legal system?
James Grant said that South Africa was proud of its constitution and had a well-respected judiciary and that its substantive criminal law was "similarly advanced and progressive and very well considered."
"The problems that we're facing are more of a systemic procedural nature.
"We have an incredibly strained police force that's not particularly well-trained -- they're massively overloaded -- and we're struggling with issues of corruption within the police force and possibly even within the prosecution service," he said.
Grant said that, regrettably, wealthier South Africans had access to better legal resources than most of their compatriots.
"Unfortunately, most South Africans don't have that extent of resources available to them. They wouldn't have available to them the best possible defense lawyers, but in a strange sense, this is not a problem unique to South Africa. Money buys for you a degree of protection. That's of course a universal problem."
In March of last year, the South African government's midterm report noted that "The effectiveness and ability of the criminal justice system to serve as a deterrent against crime is unfortunately still under threat of being undermined by the actions of a small number of those who serve in it."
It continued: "Since 2009, investigations have uncovered 1,529 persons in the criminal justice system who were possibly involved in corruption-related crime."
What are conditions like in South African jails?
South Africa's jails were put under the spotlight during the extradition hearing of Shrien Dewani, the Briton who stands accused of ordering a hitman to murder his new wife in 2010.
One of the defense's arguments -- not upheld -- against extradition was that Dewani would not be safe in South African custody.
His lawyer quoted figures from a South African report suggesting that almost half of prisoners believed sexual abuse was a feature of life in South African jails. But Dewani's request for Britain to block his extradition was declined in January of this year, and he has now been sent to South Africa.
Nooshin Erfani-Ghadimi, project coordinator for the Johannesburg-based Wits Justice Project, told CNN that South Africa's constitution and its bill of rights with regards to prisoners' rights were among the best in the world.
However, she said, overcrowding meant "unfortunately that doesn't necessarily translate into practice."
"A legacy of apartheid is that prison cells are still unfortunately a place where prisoners can be abused," Erfani-Ghadimi said.
South African public broadcaster SABC cited the Correctional Services Department as saying prisoners with disabilities were treated with dignity and enjoyed the same rights as able-bodied inmates.
However, a "statement of agreed factual findings" in the case of inmate Dudley Lee -- who contracted tuberculosis while imprisoned -- may point to a different reality. Lee said he "begged, bullied and bribed" to get the medication he needed.
CNN's Brian Walker and Richard Allen Greene contributed to this report.