Speaking to South Africa's Beeld newspaper, Barry Steenkamp said Pistorius would not be spared from suffering even if he is found not guilty over the shooting death of Reeva on Valentine's Day.
"It doesn't matter how much money he has and how good his legal team is, he will have to live with his conscience if he allows his legal team to lie for him," Barry Steenkamp said.
"But if he is telling the truth then perhaps I can forgive him one day.
"If it didn't happen the way he said it did, he must suffer, and he will suffer… only he knows."
On Friday Pistorius was granted bail as he awaits trial for the premeditated murder of his girlfriend Reeva.
The 29-year-old was shot dead in Pistorius's toilet, in what the Paralympic star claims was a tragic accident as he believed she was an intruder.
Barry Steenkamp at Reeva's memorial service (Reuters)
Beeld also reported that Reeva's mother June Steenkamp received a bouquet of flowers and a card from the Pistorius family.
"Yes, but what does it mean?" Mrs Steenkamp said.
"But also, his sister Aimee, did nothing wrong, and also his parents…they must be shattered. They are not to blame."
Reeva's family hope to set up fund in their daughter's memory to help abused women.