Kim Martin spoke on the fourth day of the sentencing section of the double-amputee Olympian’s trial.
Following the testimony, which is expected to end this week, Judge Thokozile Masipa will rule on what punishment Pistorius must receive after convicting him of culpable homicide for shooting Ms Steenkamp through his toilet door.
“My lady, I really believe the accused, Mr Pistorius, needs to pay for what he’s done,” Ms Martin told the court.
“My family are not seeking revenge. We just feel to take somebody’s life, to shoot somebody behind the door who is unarmed, who is harmless, needs sufficient punishment.”
Just after the court adjourned for lunch, Pistorius’ sister Aimee became distraught, telling her family that a man who was behind her in the gallery had mouthed an obscenity at her. Pistorius’ brother, Carl, said he would inform police about the incident.
Marc Strydom and Mikey Schultz, two men who said they were in court to support Ms Steenkamp’s family, denied any involvement in the alleged incident.
“They’re making up a fabricated story, same as Oscar’s,” Mr Schultz said. “They’re all a bunch of liars.”
Mr Schultz is a former boxer and the self-confessed killer of a businessman who escaped prosecution in an immunity deal with the state.
He has been seen sitting in court this week with two men who have had altercations with Pistorius in the past.
Pistorius was acquitted of murder for the shooting on 14 February, 2013, and found guilty of the lesser crime of negligent killing.
Judge Masipa could order a suspended sentence and a fine, house arrest, or send him to prison for up to 15 years.
Testimony in the sentencing hearing ended yesterday. The prosecution and defence said they would deliver final arguments today, clearing the way for the judge to deliver the sentence at a date to be announced.
Defence lawyers have argued for a sentence of three years of house arrest with community service. They said his disability as a double amputee who needs prosthetic legs would leave him vulnerable in jail.
Chief prosecutor Gerrie Nel has called suggestions of a house arrest sentence as “shockingly inappropriate” and wants Pistorius to be sent to prison.
Ms Martin said that she understood the rehabilitation programme in jail to be humane and dignified, contrary to allegations by one of the social workers who testified for the defence.
In her sometimes emotional testimony, Ms Martin said many people had suffered because of Pistorius, including his family, and that a sentence that excludes jail time would encourage the athlete to “feel within himself that what he’s done is all right”.
Zach Modise, the acting national commissioner for correctional services, testified after Ms Martin, saying that the South African prison system compared favourably with prisons he had visited in Britain and the US.
He acknowledged problems such as overcrowding and gang activity, but said officials had made progress in combatting those issues and that some prison facilities can cater to disabled criminals, including Pistorius. “We will be able to accommodate him,” Mr Modise said.
However, defence lawyer Barry Roux referred to reports of an increase in alleged torture in South Africa’s prison system.