Oscar Pistorius trial: Paralympian's defence dealt blow after ballistics expert accused of changing evidence mid-trial

Expert denies he changed his ballistics report in consultation with the defence to back Oscar Pistorius

Wollie Wolmarans giving evidence in the Pretoria High Court on May 9, 2014 in Pretoria, South Africa

Oscar Pistorius's defence was dealt a new blow after a key expert witness was accused of adapting his evidence and consulting details of the case to suit the athlete's version in a dramatic grilling by state prosecutor Gerrie Nel.

Returning to the witness stand, Thomas 'Wollie' Wolmarans, a former police officer, told Pretoria's High Court the crime scene was contaminated and questioned the sequence and trajectory of the bullets that pierced Reeva Steenkamp's body as the defence sought to undermine the state's case that Pistorius shot her following a heated argument.

However, under cross-examination, Mr Wolmarans came under intense scrutiny from Mr Nel, known as the 'pit bull' for his aggressive tactics, who accused him of adapting his evidence and filing a new report to back Pistorius's version of events in consultation with the defence.

"Why would you not want us to see your earlier report?," Mr Nel demanded. "Why don't you have it ready so the court can see if there's a difference between your earlier report and this one?"

Mr Wolmarans conceded that there were "ongoing" versions of his ballistics report and he kept this information in his computer "most of the time". He did not have a formal filing system in place and could not remember where his preliminary report was saved.

Continuing his evidence, the ballistics expert told the court he gave the defence a printed copy of the report on 23 April. He could not remember if he e-mailed an electronic copy before the trial started, to which Mr Nel fired back: "Why would you not be able to remember that?"

But the former policeman insisted that he did not change his report to suit Pistorius's version in consultation with his legal team, adding: "I was helped with my English but never ever was I asked to alter my report to suit the defence's case."

In a dramatic exchange, Mr Nel challenged him further, asking him if he consulted details of the case with Roger Dixon, who testified for the defence before the Easter recess.

Mr Wolmarans admitted he took him out for a beer on 16 April because he had a tough day in court and "may" have seen him again after that- he could not remember when the second meeting took place.

"My lady, he already testified, it's highly improbable that we hadn't made some discussions on the matter," he said.

"Did you, after his evidence, change anything in your report?," Mr Nel demanded, to which Mr Wolmarans replied: "It is a possibility that I changed something in my report but not anything that I discussed with him."

Oscar Pistorius (R) is greeted by his family at the Pretoria High Court on May 9, 2014, in Pretoria, South Africa (GETTY IMAGES)

Mr Wolmarans insisted that Mr Dixon, a qualified geologist, "is not a ballistic expert" and he wouldn't take his advice on the matter. The prosecutor suggested the court should do the same.

Later in his evidence, Mr Wolmarans admitted Pistorius was present in consultation but he did not ask the accused for details about the night he killed his girlfriend through a locked toilet door.

Giving a long answer, the former policeman told the court "some questions where asked" in front of Pistorius but the athlete left the consultation room and vomited after seeing a photograph of Ms Steenkamp.

"Why would that be an answer to my question, that the accused vomited, " Mr Nel told the court, addressing the witness. "You've shown your bias. You just wanted to say the accused vomited."

Pistorius is accused of murdering his girlfriend following a domestic dispute in the early hours of Valentine's Day last year. He claims he shot and killed his girlfriend in a case of mistaken identity, thinking she was an intruder.

South Africa does not have trial by jury, meaning Judge Thokozile Masipa will decide Pistorius' fate with the help of two assessors.

The murder trial continues.