Reeva Steenkamp’s mother does not believe Oscar Pistorius accidentally killed her daughter and feels “let down” by South Africa’s justice system.

In Reeva, a mother’s story, a memoir published on Monday, June Steenkamp said she believes Pistorius shot her 29-year-old daughter dead after a fight and that the couple’s relationship had been coming to an end.

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“Oscar’s story I don’t believe,” she wrote in the book, released weeks after the athlete was found not guilty of murder and sentenced to five years in prison on a lesser manslaughter charge.

Pistorius claimed that he mistook Steenkamp for an intruder, firing four shots through a locked bathroom door.

“Not one of his actions suggests he felt protective towards her,” wrote Steenkamp, the grieving mother setting out what she believes happened in the early hours of Valentine’s Day 2013.

“They had a fight, a horrible argument, and she fled to the bathroom with her mobile and locked the door.”

“I think he may have shot once and then he had to go on and kill her because she would have been able to tell the world what really happened, what he is really like.

June Steenkamp’s book about her daughter. Photo: Getty

“There is no doubt in our minds: she had decided to leave Oscar that night,” she wrote, adding that Reeva Steenkamp had indicated that the pair had not had sex.

“I believe their relationship was coming to an end. In her heart of hearts she didn’t think it was making either of them happy.”

“It was Reeva’s bad luck that she met him, because sooner or later he would have killed someone. I do believe that.”

Steenkamp added that while she forgives Pistorius, she would like to meet him to ask questions.

“I have forgiven him. I have to – that’s my religion. But I can’t forget what he has done. I hate what he has done to my child.”