Oscar Pistorius’ defence received a new blow after its own expert witness contradicted the athlete’s version of events and was accused of omitting crucial details in court.

Roger Dixon, a geologist at the University of Pretoria and former policeman, told the court his analysis of Reeva Steenkamp’s bruises and blood marks on the bathroom floor showed that the position of the magazine rack contradicted Pistorius’ version, who insists it was moved.

Referring to a graphic photograph showing a pool of blood around the toilet bowl, Mr Dixon claimed the magazine rack was close to the toilet when Ms Steenkamp was shot dead.

“Can the accused be right, if you’re right? He said the magazine rack was definitely not there. Then he must be wrong. You’re his witness,” chief prosecutor Gerrie Nel demanded.

Last week, the athlete told the court that, in retrospect, he confused the sound of the magazine rack moving for a door opening, which convinced him an intruder was about to attack him before he opened fire. The state claims he heard the magazine move after shooting Ms Steenkamp in the hip and deliberately changed aim to hit her.

Mr Dixon was later forced to admit he used a model that was 20 centimetres shorter than Pistorius on his stumps in a series of a photographs used to illustrate what neighbours could have seen from the bathroom window the night he shot and killed Reeva Steenkamp.

“Why would you not ensure that the person on its knees stands on something, is lifted to scale?” Mr Nel demanded. “Why would you not make sure that his height is exactly the height of Mr Pistorius on his stumps?”

“It is something I omitted, I overlooked it at the time,” Mr Dixon replied, insisting he was not trying to “mislead” the court. The test is important because Dr Johan Stipp, a neighbour of Pistorius, previously testified he saw a man moving in the bathroom from his house.

Mr Dixon came under renewed pressure from Mr Nel, who accused him of being unqualified to testify as an expert witness as he challenged the state's murder case. He conceded he had no qualifications in ballistics or pathology, and was not affiliated to a forensic body.

Returning to the witness stand, Mr Dixon wrote on Facebook: “Third day in court today. Let’s see how much of my credibility, integrity and professional reputation is destroyed.”

He also lashed out at “those who will not listen because it is not what they want to hear” and wrote he was looking forward to having a drink after finishing his evidence.

On Wednesday, Mr Dixon challenged the prosecution claiming Ms Steenkamp was standing at an angle to the toilet door with her hand “on the door handle”, suggesting she was in the process of opening the door, when four shots struck her in quick succession.

At the start of the trial, the state's ballistic expert, Captain Chris Mangena, told the court Ms Steenkamp was standing facing the door when the first shot hit her in the hip, the second shot missed her, hitting the cubicle instead and causing it to break into pieces, bruising her back.

Ms Steenkamp then fell on top of the magazine rack in a seated position, before she was hit in the arm and head as she tried to protect herself from the bullets. Capt Mangena noted there could have been a short break between the first and the second shot, giving her time to scream.

Pistorius is accused of murdering girlfriend Reeva Steenkamp 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.

The trial has now adjourned for a break and will reconvene on Monday 5 May.

•Credit (except for headline): The Independent (Britain). Photo shows Oscar Pistorius.

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