By Nick Butler

It was a potentially seminal day in the trial of Oscar Pistorius today as one of the key prosecution claims was challenged ©Getty ImagesKey elements in the prosecution case into the death of Reeva Steenkamp have been challenged today, after one of the most respected ballistics experts in the country claimed the South African was not in a defensive position when she was killed.

Steenkamp was shot dead by boyfriend Oscar Pistorius multiple times through a bathroom door on Valentine's Day last year after the six-time Paralympic gold medal winner claims he mistook her for an intruder in their Pretoria home.

In an integral part of the prosecution evidence earlier in the trial, a police ballistics expert had cowered with his hands over his head, imitating the position he thought Steenkamp was in when she was killed.

This was used by Prosecutor Gerrie Nel to suggest Pistorius had argued with Steenkamp, with the fact she was crouched defensively when she was killed thus supporting Nel's case she knew what was coming.

But former police officer Tom Wolmarans today claimed Steenkamp could not have had her hand over her head when Pistorius fired four bullets at her, suggesting she was taken by surprise.

"The left hand cannot have been against her head, because there were no wounds, and no brain tissue on the inside of her hand," he said.

Retired forensics expert Tom Wolmarans testified for the defence on the latest day of the trial today ©AFP/Getty ImagesRetired forensics expert Tom Wolmarans testified for the defence on the latest day of the trial ©AFP/Getty Images

Wolmarans testimony was attacked by Nel in the cross-examination stage, as the prosecutor demanded to know how many different versions of his analysis he had given the defence team, whom he consulted about it and whether he had changed any of his report.

Nel also disputed the former police officer's description of where Steenkamp was when the final bullet hit her in the head, claiming that if her position was as Wolmarans described it, there would have been no space for her head. 

In one of the few light-hearted moments in the trial so far, Wolmarans also at one point stepped inside the court's reconstructed toilet cubicle to demonstrate Steenkamp's position

He closed the door as he stepped into the toilet cubicle, before prompting laughter in court by calling to judge Thokozile Masipa and saying: "I'm sorry, my lady, you can't see me".

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