PRETORIA, South Africa >> Oscar Pistorius’ lawyers at his murder trial Wednesday tried to roll back the prosecution’s momentum, but the prosecutor sharply questioned the credentials and findings of a forensic expert for the defense.

Following the tough cross-examination of Pistorius that lasted five days, his defense attempted to re-assert his story that his killed his girlfriend by mistake, but the prosecutor strongly challenged the expert witness.

Roger Dixon, a forensic geologist at the University of Pretoria and a former policeman, contradicted parts of the evidence given by a police ballistics expert and the state pathologist who examined the body of Reeva Steenkamp, fatally shot last year by Pistorius. But Dixon acknowledged that he did not have expertise in some of the areas in which he was testifying, including sound, light and ballistics.

Prosecutor Gerrie Nel was sometimes sarcastic while questioning Dixon, subjecting him to the same grueling scrutiny with which he challenged Pistorius, who often fumbled for answers while in the witness box.

Dixon offered a different version for the order of the shots that killed Steenkamp in an attempt to back up Pistorius’ version of a mistaken shooting and rebuild his case after the Olympic athlete’s shaky testimony. He said it was his opinion that Steenkamp was hit in the hip and the arm in quick succession by the first two of four shots while she was standing close to the door, and indicated he believed she may have had her right arm extended and maybe her hand on the door handle, as if she was about to open the door through which she was shot.

The defense was using Dixon’s testimony to try to cast doubt on the prosecution’s version that Steenkamp fled to the bathroom and was hiding in the toilet during a fight with Pistorius in the pre-dawn hours of Feb. 14, 2013.

Nel has said that the double-amputee athlete shot Steenkamp through the door as she faced him and while they were arguing.

Pistorius, 27, is charged with premeditated murder for Steenkamp’s shooting death and faces 25 years to life in prison if convicted on the charge. He claims he shot the 29-year-old model by mistake thinking she was a dangerous intruder in the toilet about to come out and attack him.

Dixon also said he took part in audio tests conducted by experts for the defense that showed the sounds of gunshots and of a cricket bat hitting a door were similar and could be confused. The difference is important because several neighbors have testified that they heard Steenkamp scream before shots on Valentine’s Day last year, backing the prosecution’s case that there was a fight before Pistorius shot his girlfriend with his 9 mm pistol. Pistorius’ defense says the witnesses are mistaking the sequence and they heard Pistorius screaming in a high-pitched voice for help before breaking the door open with the bat to get to Steenkamp.

In a cutting statement on Dixon’s finding regarding Steenkamp’s wounds, Nel said to Dixon: “I use the word ‘finding’ very loosely.”

Nel also questioned Dixon’s role in the audio test involving the sounds of gunshots and a bat that was played by defense lawyers during Dixon’s testimony.

“Your expertise (in the audio test) was wielding the cricket bat?” Nel asked Dixon sarcastically.

Dixon replied: “My part of that test was to wield the cricket bat to produce the sound.”

On questioning by Nel, Dixon conceded the tests had to be done a second time because of problems with the first test, and they were recorded by a music producer who had no experience in recording gunshots.

Earlier, Judge Thokozile Masipa ruled that proceedings will adjourn for more than two weeks after Thursday and resume again on May 5.