PRETORIA, South Africa (AP) -- An expert witness for the defense at the murder trial of Oscar Pistorius was supposed to help the athlete's assertion that he killed his girlfriend by mistake last year, but he ended his testimony on Thursday amid blistering attacks on his credibility by a prosecutor who accused him of slipshod analysis and fuzzy explanations.
Roger Dixon, a former forensic scientist for the South African police, was frequently on the back foot as he tried to fend off sharp questions from chief prosecutor Gerrie Nel, who says Pistorius is lying and fatally shot Steenkamp on purpose after a nighttime argument in his home. For nearly a week, the double-amputee runner was subjected to the same kind of harsh scrutiny when he testified that fear led him to fire four shots through a toilet door at what he thought was an intruder.
Legal analysts say Judge Thokozile Masipa will review the mass of testimony in its totality, which is said to be almost 2,000 pages so far, and that it can be misleading to assess the course of the trial by a single witness. Defense lawyer Barry Roux, for example, hounded police witnesses with questions about alleged mishandling of evidence at the house where Pistorius killed Steenkamp in the early hours of Feb. 14, 2013.
Masipa, who will deliver a verdict on the premeditated murder charge against Pistorius, adjourned the trial until May 5.
Dixon, now a geologist at the University of Pretoria, was forced to acknowledge Wednesday that he had no expertise in light and sound measurement, as well as pathology and ballistics, despite his commenting on those topics while testifying about the circumstances of Steenkamp's death.
On Thursday, Nel resumed his attack, criticizing Dixon's work after the geologist did not use Pistorius' exact height when standing on his stumps. The prosecutor questioned why his measurements were 20 centimeters (eight inches) shorter in a test to see if Pistorius' head and body would have been high enough to be seen by a neighbor through a window of his bathroom.
''It is something I omitted. I overlooked it at the time,'' Dixon said, adding that he was not trying to ''mislead'' the court.
Nel also questioned Dixon's statement that he conducted tests showing that Pistorius' bedroom is very dark at night and with the curtains closed, a conclusion that would support the athlete's contention that his inability to see his girlfriend on the night that he killed her contributed to the shooting. Nel noted that Dixon judged how dark it was without using any light-measuring equipment.
''What one can see using your eyes is a very subjective thing,'' Nel said.
''I wanted to see what I could see,'' Dixon replied. ''A measurement doesn't translate to me into what I'm actually seeing.''
Nel also said Dixon was giving convoluted responses, addressing the judge: ''My lady, may I just ask the witness which question he's answering at the moment?''
Another time, Dixon picked up a prosthetic leg of Pistorius that had been included as trial evidence while discussing varnish traces that he said were found on the prosthesis and he matched to the door varnish. The defense has cited that as proof that the Paralympic champion tried to kick down the door to get to Steenkamp after realizing, according to his version, he had shot her by mistake. Then the prosecutor chided Dixon for not bringing the varnish sample to court.
Dixon appeared serene throughout the rough-and-tumble of his cross-examination. Asked if he knew the state's case and other trial details, he said:
''I am not like most people. I do not have a television set. I do not have a radio at home.''
His Twitter handle reads: ''I am a mineralogist and forensic scientist, I grow clivias and other plants, have a landrover and a Trans Am. I live in a forest I planted myself.''
He acknowledged the pressure from the feisty prosecutor in a message on his Facebook account that was apparently posted on Thursday morning. He confirmed its authenticity when questioned by journalists. It read:
''Third day in court today. Let's see how much of my credibility, integrity and professional reputation is destroyed. It is difficult to get belief in those who will not listen because it is not what they want to hear. After that, beer!''
Torchia reported from Johannesburg.