The South African, who is due to be sentenced on Wednesday 6th July 2016 for the murder of Reeva Steenkamp, has described finding her body on Valentine's Day.
During an interview with investigative journalist, Mark Williams-Thomas which was broadcast by ITV on Friday night, he said: "I am screaming, I am just praying for the Lord and I am saying: 'God please, please, please, please, please, please'.
"I opened the toilet door and immediately when I saw Reeva she was over the toilet. She had slumped over the toilet and at [that] point I knew I had killed her and I knew that she was dead. I went down on my knees and pulled her on to me."
Pistorius was initially sentenced to five years in prison - and served one year before being moved to house arrest - after being found guilty in 2014 of manslaughter for Steenkamp's killing.
That ruling was overturned by South Africa's Supreme Court last year and Pistorius was convicted of murder.
The double amputee also told ITV: "I don't want to to back to jail and I don't want to have to waste my life sitting there. If I was afforded the opportunity of redemption, I would like to help the less fortunate.
"I would like to believe that if Reeva could look down upon me, that she would want me to live that life."
Pistorius has a Bible verse from 1 Corinthians tattooed on his shoulder and has spoken in recent years about the hope he places in God.
South Africa has a minimum sentence of 15 years in prison for murder, although a judge can reduce that in some circumstances.
Judge Thokozile Masipa, the judge who initially acquitted Pistorius of murder at his trial, is presiding over the sentencing hearings and will decide his new sentence.