Day four of Oscar Pistorius' sentencing hearing resumed Thursday morning, with Reeva Steenkamp's cousin declaring that the South African athlete deserves jail time for killing his girlfriend.

Pistorius, a famed Paralympic athlete nicknamed the "Blade Runner," fatally shot Steenkamp on Feb. 14, 2013. The Olympic champ pleaded not guilty to first degree murder, arguing that he shot her by mistake because he thought she was a home intruder.

Last month, he was found not guilty of first degree murder, but guilty of culpable homicide, a lesser charge also known as manslaughter. The Blade Runner now faces anywhere between 15 years to 0 years in prison, with a hefty fine, report Fox News.

On Thursday, Steenkamp's relative Kim Martin pleaded with Judge Thokozile Matilda Masipa to sentence Pistorius to serve time behind bars.

Pistorius should be given "sufficient punishment" for killing Steenkamp, she said at the hearing in Pretoria, adding that he "needs to pay for what he has done," reports BBC.

"My family are not people who are seeking revenge, we just feel that to shoot somebody behind a door that is unarmed, that is harmless, needs sufficient punishment," she added.

Prisons chief Moleko Modise of South Africa's Correctional Services also testified on Thursday that Pistorius would be safe in prison, despite claims from a defense witness who said the disabled athlete would be "broken" by prison. Instead, his lawyers argue that he should be put on house arrest and order to community service for the killing.

Martin also delivered an emotional testimony on Tuesday about the late model, saying that her world ended when she found out on a car radio that the 29-year-old law graduate had been fatally shot.

"I was trying to phone her (Reeva) and she wasn't answering and I was screaming at my husband," Martin recalled, according to the Associated Press.

Martin said she got confirmation that the dreadful news was true when she went to her mother's home and found her mother crying uncontrollably.

"The doors opened and my mother was hysterical and that's when I knew it was true. That was for me the end of the world. Everything was just a blur from then onwards."

According to Martin, Steenkamp's mother June was on medication after the killing while her father sat in a corner of his house crying. She also said that she is receiving trauma counseling and her children need therapy.

The tragedy "ruined our whole family," she said. "It's ruined uncle Barry and auntie June. Reeva was everything to them. She was their only child in PE [Port Elizabeth] for a long time and they absolutely adored her. They were so proud of her, what she'd accomplished. She looked after them so well, not just financially," she said, according to The Guardian.

Judge Masipa will likely issue a sentence early next week, according to BBC.