Pretoria: In a pummelling cross-examination the prosecution called Oscar Pistorius' account of killing his girlfriend "impossible" yesterday, zeroing in on apparent inconsistencies in key parts of his testimony.

Oscar Pistorius. Pic/Getty Images
Oscar Pistorius. Pic/Getty Images 

"Your version is so improbable that nobody would ever think it's reasonably, possibly true it's so impossible," Prosecutor Gerrie Nel thundered during his second day interrogating the Olympian.

Nel also rubbished the athlete's claim that police moved important pieces of evidence after arriving at the scene early on Valentine's Day morning last year. Pistorius said police moved fans, put the duvet on the floor and opened the curtains when they came to his villa, implying they had tampered with the crime scene.

"Is this one big conspiracy? They would do all this to you" asked Nel with incredulity."

Pistorius, known as the Blade Runner for his j-shaped prosthetic legs, has been charged with intentionally murdering his 29-year-old model girlfriend after shooting her four times through a locked toilet door. He faces a life sentence if convicted.

The double-amputee has said he fired the shots mistaking Steenkamp to be an intruder, but Nel said: "We know for a fact there were no intruders in your house that night, we know for a fact there was no ladder against the wall. We know for a fact that you had no reason to shoot, objectively speaking."