The murder trial of ­Olympic and Paralympic sprinter Oscar Pistorius has been adjourned until May 5 after the state wrapped up its cross-examination of a forensic expert brought by the defence.

Judge Thokozile Masipa granted the state's request for a postponement to avoid conflicts with other cases.

Prosecutor Gerrie Nel - nicknamed "The Pitbull" for his aggressive style - tore into defence witness Roger Dixon over three days, ­questioning his credibility and expertise.

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Pistorius, 27, is on trial for the murder of his girlfriend Reeva Steenkamp, whom he shot dead with four rounds from a 9mm pistol on Valentine's Day last year. The athlete insists he killed the 29-year-old law graduate and model after mistaking her for an intruder.

Mr Dixon, a forensic geologist and former police officer, testified that Ms Steenkamp was standing at an angle to the door with her arm out in front of her, suggesting she was reaching for the handle, when Pistorius shot her dead.

The testimony challenged the version of the state, which has sought to portray Pistorius as a gun-obsessed hot-head who murdered Ms Steenkamp after an argument.

Mr Nel heaped scorn on Dixon's expertise, prompting Judge Masipa to tell the advocate to restrain himself.

When the geologist said on Wednesday that he tested the sound of a cricket bat hitting a wooden door to see if it could be confused with the sound of a gun shot, Mr Nel asked: "Do you need to be an expert to do that? What expert skills did you use, wielding a bat?"

At another point, Mr Dixon confessed to being a "layman" with no professional experience in blood spatter analysis, forensic pathology or ballistics.

After asking Mr Dixon for another of his findings, Mr Nel added: "I use the word 'finding' loosely".

The globally high-profile trial is due to resume two days before South Africa goes to the polls for a national election.

Defence advocate Barry Roux is expected to call his next witness once the trial resumes.