JOHANNESBURG (AFP) - South African prosecutors who have accused Oscar Pistorius of murder now admit he may not have had his prostheses on when he fired the shots that killed his girlfriend, removing a key argument for premeditation.

According to a document obtained by local television news channel eNCA, the state's own ballistics expert believes Paralympic star Pistorius was "most likely" on his stumps when he shot Reeva Steenkamp through the bathroom door.

During an extensive bail hearing, prosecutors had argued that Pistorius took time to put on his prosthetic legs before firing the shots through the locked bathroom door, showing he was not panicked by the prospect of an intruder.

Pistorius, who goes on trial March 3, denies the charge of murder and says he mistook Steenkamp for an intruder.

ENCA also reported that prosecutors believe security guards at Pistorius's gated community called the Olympian after the shooting to see if everything was okay, and that he said it was fine and did not require assistance.

They also believe that a neighbour who lives less than 100 metres away, heard shouting on Valentine's Day, the night of Steenkamp's death.

The National Prosecuting Authority said it had not leaked the documents.

"The defence has access to everything, to the docket and all evidential material we have," said spokesman Nathi Mncube.

"We don't give anything to any other person other than the defence and if it gets leak, it won't be us, we can't do that because it's damaging to our case."

Pistorius, 27, whose legs were amputated below the knee when he was a young boy, is known worldwide as the "Blade Runner" for competing on two fibre-optic blades and running against able-bodied athletes in the London 2012 Olympic Games.