A forensics expert hired by Oscar Pistorius's defence team has claimed that police have so-far refused to let him examine the bullet-hole-riddled bathroom door which Reeva Steenkamp was behind when she was killed.

Reggie Perumal, regarded as one of South Africa's leading forensic scientists, says that he is still waiting to see the crucial piece of evidence more than two weeks after the Valentine's Day death, which has generated a global media storm.

Prosecutors contend that following a furious argument in the early hours, Pistorius's girlfriend, model Reeva Steenkamp, 29, was in the lavatory when the Paralympic star fired four bullets through the door with a 9mm handgun, murdering her; Pistorius, 26, denies the charges and claims that he fired the bullets in panic, mistaking Steenkamp for an intruder.

Perumal, 57, told the Sunday Times that the door was removed by police. "We have asked the police for it but we don't know where it is. We need access to the door. It's the most crucial piece of evidence in this case. The question I have is 'Why won't the prosecution hand it over?'"

The question of the trajectory of the bullets as they hit the door is crucial for both the defence and prosecution. Pistorius claims that when he fired the gun he felt at risk as he was not wearing his artificial limbs, the police contend that evidence indicates he was wearing them.

"Next to the post-mortem results, this is the most crucial information needed," said Perumal.

"It's critical that the defence examines this door so that we can see the trajectory of the bullets and examine exactly whether Pistorius was wearing his prosthetic limbs, but also where Steenkamp was in the toilet when she was shot."

The South African police have come under intense scrutiny following the killing, with it being revealed that Hilton Botha, the officer leading the investigation, had failed to wear protective clothing when walking through the crime scene and that he had failed to detect a bullet casing Pistorius's legal team found in the toilet bowl.

When it was also revealed that he faced seven charges of attempted murder he was replaced by the South African police chief.

More pressure has been piled on the force after footage emerged showing officers dragging the body of a man behind a police van before he died in custody.

Both sides have been accused of leaking information to the media in an effort to tip public sympathy to their side.

Recently the Pistorius camp revealed that he had held a private remembrance service for Steenkamp after being freed on bail.

However, Perumal said that having been present at Steenkamp's autopsy, he was in a position to rule out rumours that her head had been crushed by a cricket bat and that she was pregnant when she died.

"The facts are there, I concur with the state autopsy and their findings. I was there." He said. "The victim died from gunshot wounds. There were no signs of physical assault on her by Oscar Pistorius, whether with a bat or anything else."

He said that rumours that Steenkamp's body was found clutching a clump of Pistorius' hair were also false: "We even have photos of her hands and there were only two strands of hair and they were her own long, blonde hairs."

Pistorius's trial is scheduled to begin on 4 June.