The Paralympic athlete killed Reeva Steenkamp, a model and law graduate, in the early hours of Valentine's Day in 2013, saying he mistook her for a burglar when he fired four times through the door of his bedroom toilet.
In March, Pistorius's lawyers failed in their legal bid to reverse a Supreme Court of Appeal judgement that upgraded his original conviction from culpable homicide -- the equivalent of manslaughter -- to murder.
Psychologist says Pistorius 'not able to testify'
"It has been very difficult for me to forgive... I feel that Oscar has to pay for what he did. He has to pay for his crime," Barry Steenkamp, 73, said shaking with emotion and in tears.
"She must have been in so much fear and pain," he said, reliving the horror of learning how she was killed. "It must have been absolutely awful."
Pistorius faces return to jail for lover's murder
He also said that he believed the couple had argued on the night of the murder -- disputing Pistorius's claims.
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