Oscar trial: Expert’s credibility under fireComment on this story
** This story has been updated
Pretoria - The credentials, credibility and integrity of one of Oscar Pistorius's defence's experts have come under fire.
Roger Dixon, a forensic geologist, was asked about the reports he provided to the defence on the lighting conditions of Pistorius’s home, sound tests and his analysis of the bathroom door Pistorius shot through the night he killed Reeva Steenkamp.
Dixon said some changes had been made to his reports as he continued his own investigation over the past year, but could not remember any specifics.
Dixon's sound testing of a cricket bat and then a firearm against a door similar to Pistorius's bathroom door was also brought intoquestion.
According to State prosecutor Gerrie Nel, Dixon had failed to explain who had fired, what equipment or recording devices were used, or any other details of the test.
Dixon admitted no decibel tests were conducted between the two tests.
Nel said that the lower decibel sounds would get fainter over a distance, but Dixon said he could not comment on this.
The lawyer also pointed out that the tests were reconducted as late as last week at a shooting range, but Dixon said he was not part of this.
Dixon said the defence team's ballistic experts had used a gun similar to Pistorius's in this newer test.
Dixon said the first test had shown that the gun had jammed after each bullet was fired, meaning the team wanted to re-do the test to fire the four shots consecutively. Pistorius has claimed that he fired four times in quick succession on the night of the shooting.
Nel then tried to attack Dixon's integrity by suggesting he was not forthcoming with this information.
But Dixon said it was for precisely this reason, so the defence wouldn't have to edit the sound sample, that a second test was conducted. Dixon said he had forgotten to mention all of this in his evidence in chief.
The expert also told the court that a music producer had been responsible for the recording, prompting Nel to ask if this person was “an expert in recording explosive sounds”.
Dixon said he wasn't sure.
Nel asked if Dixon had ever heard a version of the gunshots fired on the first night that had been electronically altered to sound like rapid fire. Dixon said he had not.
Nel then asked if Dixon had any expertise in “wound ballistics”, like the State's pathologist Gert Saayman.
Dixon said he did not.
Nel moved onto Dixon's theory of the bullets that hit Steenkamp.
Dixon had earlier said that all of the bullets hit Steenkamp in some capacity, with one ricocheting off the wall after going through the webbing of Steenkamp's hand. Dixon said he believed that the third bullet (C) had been responsible for this ricochet.
But Nel said that the State forensic expert had used a laser to determine the only bullet hole that aligned with the damage to the wall was the second bullet (B).
Dixon was unable to answer if the defence's other ballistic expert had agree with his hypothesis.
Nel asked about the “witness board” that had been used to determine the number of splinters that had been blown through the door. He accused Dixon of not providing images of the entire board.
Dixon said that these boards are designed to show trends of the spray, and that they were used to determine whether the marks on Steenkamp's arms could have been casued by flying splinters.
Nel said that Dixon was not a wound ballistic expert but had the audacity to say Saayman had made a mistake.
Dixon said Saayman had not made categoric statements in his report, and that his own analysis was different.
Earlier, Nel began his cross-examination by asking about Dixon's credentials and analytical method.
Nel said Dixon had not taken the court through the processes he'd gone through to come to his conclusions.
“What I've testified on now, that information was gained from reports by other expert witnesses,” said Dixon, who had added his own analysis to reconstruct the scene and order of events.
Dixon said he had experience analysing fingerprints, footprints and other marks for the SAPS.
Nel also asked why Dixon had been brought to testify about the sounds of the cricket bat and the gun, despite not being a sound expert. Dixon said his expertise was to reconstruct the situation of the night of the shooting, and that he hadn't been part of the analysis of the sounds.
Dixon said he was accompanied by ballistics experts when conducting this test.
Nel then moved onto Dixon's analysis of the lighting conditions at Pistorius's home.
On Tuesday, Dixon said that when the curtains were drawn on a moonless night, the bedroom was pitch black.
Dixon said he had simply used his eyes to make this determination.
The expert also clarified that fibres found on the door were examined under a microscope to determine that they were part of Pistorius's sock. This showed the athlete had tried to kick down the door with his prosthetic legs.
But he said he'd never examined the socks themselves closely, but had seen pictures of them.
Nel suggested that because the expert had only seen images of the socks, he had no way of making a scientific finding around them.
The prosecutor then asked if Dixon was a blood spatter analyst, and he replied he had received no formal training in this field.
Nel said Dixon indicated a finding of how a door panel had been in contact with blood.
Nel said that if Dixon was employed at the forensic science laboratory, he would have to undergo many proficiency tests per year as an expert. But because Dixon no longer works for them, he said he had not been subject to these since 2011 or 2012.
On Tuesday, Dixon said the marks on the door were created by a cricket bat, and Nel asked if he had physically matched Pistorius's bat to the door.
Dixon said the grooves and shape of the bat, which he had held up against the door, meant this could be inferred.
Nel added that Dixon had failed to meet with the State's forensic experts. Dixon said he had read their reports to come to his findings.
The prosecutor then said that Dixon had failed to draft a report on all of his testimony.
Dixon said he had written multiple reports for the defence.
Nel asked Dixon about his hypothesis that if Steenkamp had been hit by multiple projectiles, they could have each pushed her back further into the bathroom.
The prosecutor said this was impossible, and was more likely something one would see in a movie.
Dixon recanted what he had said earlier, saying the bullet had made Steenkamp more unstable.
Nel also pointed out the marks on Reeva Steenkamp’s back, and said these were not present during the post-mortem, and were likely to become more accentuated, not disappear overnight.
“I am not a wounds expert, I am not a pathologist,” said Dixon.
Nel repeated that Dixon was not at the post-mortem, and thus had made his analysis only through photographs and reports.
Earlier, Dixon had said he believed these marks were caused by Steenkamp falling on the toilet cubicle’s magazine rack after she was shot.
Nel said that in the state’s autopsy report, the bruise was explained, and he asked how Dixon could dispute it.
Dixon even admitted he had a layman’s understanding of the report - and ballistics - and was not a forensic pathologist.
“Do you see how irresponsible it is to make inferences in areas where you’re not an expert?” asked Nel.
Dixon revealed he had originally been brought onto the case because it was thought primer residue could be important, speaking more to his field as a forensic geologist.
He also examined the varnish that had scraped onto Pistorius’ prosthetic legs when he kicked the cubicle door.
The expert also admitted that the test the defence team had conducted used different ammunition from Pistorius when they tried to recreate the noises of shooting through and hitting the bathroom door with a cricket bat.