The authors of a new book looking at the forensic evidence of Reeva Steenkamp's death claim Oscar Pistorius attacked her with a cricket bat before he shot her.
Brother authors Calvin and Thomas Mollett reviewed forensic evidence from the investigation into Ms Steenkamp's death for their book Oscar vs The Truth, and say injuries to her back are consistent with being struck by a cricket bat.
Two oval bruises on the model's back were previously attributed to her falling on a magazine rack as she was shot.
The brothers say the bruises could have been made by the corner of the cricket bat that Pistorius told the court he used to break down the lavatory door.
They note a bruise on the model's bottom and a scrape to her nipple that were unexplained, and suggest damage to the rubber around the bat's handle would not have been sustained in the "three to four blows" Pistorius said he used to break down the door, after he realised Ms Steenkamp wasn't an intruder.
"Is this how the rubber would have looked after only four blows, hard blows as they might have been? Or were there other blows and action with the bat as well? Was there some pulling and twisting on the rubber while one person tried to take the bat from another?"
The Mollett brothers are amateur investigators and have previously looked into other controversial cases South Africa.
They also say police investigating the shooting contaminated the scene, for example by walking over the lavatory door and moving the gun.
"One gets the impression that police arrived on the scene and thought they had an open-and-shut case against Oscar," the authors write. "They knew he pulled the trigger, and had statements from the neighbours who heard a woman scream -- why bother doing a proper forensic investigation?"
The brothers say the police also overlooked vital clues, such as possible drag marks made in the bloodstains by Pistorius walking on his stumps, and unexplained damage done to a metal plate near the model's body.
Ms Steenkamp died on Valentine's Day in 2013.
Pistorius was originally convicted of culpable homicide (equivalent to manslaughter) after claiming he'd mistaken her for an intruder.
That conviction was overturned, and the athlete found guilty of murder last December.
He'll be sentenced next month.